antibiotic resistance in the microbial world 13 an...

Review of Literature

Antibiotic resistance in the microbial world

An historical overview of antibiotics

The antibiotics field was initiated when Paul Ehrlich first

coined the term 'magic bullet', or chemotherapy, to designate

the use of antimicrobial compounds to treat microbial

infections. In 1910, Ehrlich discovered the first antibiotic drug,

Salvarsan, which was used against syphilis. Ehrlich was

followed by Alexander Fleming, who discovered penicillin by

accident in 1928. Then, in the 1935, Gerhard Domagk discovered

the sulfa drugs, thereby paving the way to the discovery of the

anti-TB drug Isoniazid. Then, in 1939, Rene Dubos became the

first scientist to discover an antibiotic after purposely looking

for it in soil microbes. Dubos discovered Gramicidin, which is

still used today to treat skin infections. Finally, in 1943, the first

TB drug, Streptomycin, was discovered by Selman Waksman

and Albert Schatz. Waksman was also the one who coined the

term 'antibiotics'. Thus, antibiotics have been used to treat

bacterial infections since the 1940s [Davey 2000, and Jacoby

1999].

The basic characteristics of antibiotics

Today, there are about 4000 compounds with antibiotic

properties. Antibiotics are used to treat and prevent infections,

and to promote growth in animals.

Antibiotics are derived from three sources: moulds or fungi,

bacteria, or synthetic or semi-synthetic compounds.

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They can be used either internally or topically, and their

function is to either inhibit the growth of pathogens or to kill

them. Antibiotics can thus be divided into Bacteriostatic drugs,

which merely inhibit the growth of the pathogen, and

Bacteriocidal drugs, which actually kill the bacteria. However,

the distinction is not absolute, and depends on the drug

concentra tion, the bacterial species, and the phase of growth.

Antibiotics are more effective against actively growing bacteria,

than against non-growing persisters or spores. When two

antibiotics are used in combination, the effect could be additive,

synergistic, or antagonistic.

Antibiotics can also be divided into broad-spectrum and

narrow-spectrum antibiotics. For example, Tetracycline, a broad

spectrum antibiotic, is active against Gram positive bacteria,

Gram negative bacteria, and even against mycobacteria;

whereas penicillin, which has a relatively narrow spectrum, can

be used mainly against Gram positive bacteria. Other

antibiotics, such as Pyrazinamide, have an even narrower

spectrum, and can be used merely against Mycobacteriulll

tuberculosis.

Modes of action of antibiotics

Antibiotics fight against bacteria by inhibiting certain vital

processes of bacterial cells or metabolism. Based on these

processes, antibiotics can be divided into five major classes

[Brotz-Oesterhelt and Brunner 2008]:

.,. Cell wall inhibitors, such as penicillin and vancomycin

14


" Inhibitors of nucleic acid synthesis, such as

fluoroquinolones, which inhibits DNA synthesis, and

rifampin, which inhibits RNA synthesis

" Protein synthesis inhibitors, such as aminoglycoside

" Anti-metabolites, such as the sulfa drugs

" Antibiotics that can damage the membrane of the cell,

such as polymyxin B, gramicidin and daptomycin

eel Wall Synlher.is ~ V8t~"1dO

Bedlracin

"""""'on. c~

Ceph;unyons

Cell Wall Integrity ~.IactlIm_.

Translation::~~""------~~""~""'~~ ProCein~ $ynl/le$i$ ProIein Syntl1esis (50S Inh0tM40t$) (30S In/1ItJi1OfS) E~ T"'~ ~ S<r~ OndamY"" Spocao ... ",on u""""""",, Konamyon

Cytoplasmic Membrane

~ PhOSpholipid Membranes

Figure 2.1 Mode of actions of antibiotics [Pratt 2004]

15


The Table 2.1 is a summary of the types or classes of antibiotics

and their properties including their biological source, spectrum

and mode of action [Todar 2004].

Table 2.1 Classes of antibiotics and their properties [Todar 2004]

Chemical class Examples Biological source Spectrum Mode of action (effective against)

Beta-lactams Penicillin G, PellicilliulII Gram-positi \'€, Inhibits steps in (penicillins and Cephalothin /lOrl/rllll! <lnd bcKtcria cell wall cephalosporins) (peptidoglycan)

5vnthesis and

C('/)lll7lo~/)()rilll}IS murein

pecil's assembly

Semisynthetic Ampicillin, GTiJIll-positi\'c Inhibils steps in beta-lactams Amoxicil1in dnd Cram- cell wall

negathT' bacteria (peptidoglycan) s\'nthesis and murein

assembly

Clavulanic Acid Augml'ntin is SlrcplolllY('l'S Cram-positi\'e Inhibitor of

cbvubnic acid cI llVlIi igt' rus and CrJ.rn- bacteritil beta-plus AmoAiciliin negali ve bacteria lactamas~s

Monobactams AzlreClnal11 01 nllll(J/mc feri 111)1 Cram-positive Inhibits steps in I!jolacclIlIl and Cram- cell wall

m'gativ(' bactl'ria (peptidoglycan) synthesis and murein assembly

Carboxypenems Imipt'nl.'m SIrcFiolllYCC5 Cram-positin:~ Inhibits steps in cattlcyll and Gram- cell wall

negative bacteria (peptidoglycan) synthesis and murein assembly

Aminoglycosids Streptomycin 51 I"LptOIll ycc::: gri:::fu::: Cram-positive Inhibits ,mel Cram- translation negative bacteria (protein

synthesis)

16


Chemical class Examples Biological source Spectrum lVlode of action (effective against)

17

Gentamicin A1icnmlllllospom Cralll-pasiti \'e Inhibits species and Cram- trans]"tion

negative ba.cteria (protein esp. PsclIdolJlUIlI1S synthesis)

Glycopeptides Vancolll\'cin Alllycoil1topsi5 Cram-positive Inhibits steps in orit'lll{/ii~No(a}'di(/ badl'rid, esp. mUTl'in oricil tlllis(formcrly SlnpllylococC//s (peptidoglycan) designated) IlIlYL'/IS biosynthesis

and assembly

Lincomyci ns Clindamycin Sln'll/oIllYccs Cram-positive Inhibits !illeo/llcllsi" and Cralll- translation

negative bacteria (protein esp. syntheSis) afklC'fO hie Bactcrois

Macrolides Erythroll1:"cin, Stl'CptOlllYCCS Cram-positive Inhibit Azithromycin cryfhreus bcKteria, Gram- translation

neg,ltive bacteria (protein not syntheSis) enterics, Neisseria, LcSiolld/l1, MycoplllSlll1l

Polypeptides Polymyxin Bilcilllls polylllyxa Gram-negative Damages bactt;'ria cytoplasmic

membranes

Bacitracin Bilcill1l5 slIl1tilis Cram-positive Inhibits steps in bactt.'rid murein

(peptidoglycan) biosynthesis and assemblv

Polyenes Amphotericin Slrcplolllyt"{'s fungi Indctivatc 1l0dOS/IS (l-I i S tOpiIlSIIlI1) membranes

containing stE'rols

Nystatin Strcpto/J/YCf!S Fungi (Calldido) Indctivate /lOurSCI membranes

containing


Chemical class Examples Biological source Spectrum Mode of action (effective 18 against)

stewls

Rifarnycins Rifampicin SlrcI'iOlIlYCCo;; Cr,llll-positive Inhibits IIIcriitcrn1l1ci and Cram- transcription

negative bacteria, (bacteri"i RNA MycohilCfcriulI1 polymerase) tllberculosis

Tetracyclines Tetracycline Sf fc}/II 1I11yCC5S pecies Gram-positi \'12 Inhibit and Crcllll- tran~btiol1

negiltive bacteria, (protein Rickettsias synthesis)

Semisynthetic Doxycycline Gram-positivE' Inhibit tetracycline Jnd Cram- translation

negative bacteria, (proh.'in Rickettsias synthesis) Ehrlichia, Borrelia

Chloramphenicol Chloramphenicol Slrcp/oIIIYCL'5 GrJn1-positi\'e Inhibits z'e/fez IIC/Ilt' and Gram- tral151,ltiol1

negali ve bacteria (protein synthesis)

Quinolones Nalidixic acid synthetic ~lainly Cram- Inhibits DNA llegJtive bacteria replication

Fluoroquinolones Ciprofloxacin synthetic Gram-negali\"e Inhibits DNA and some Cram- replication positive bacteria (Bacillus tlllfhmo's)

Growth factor Sulfanilamide, svnthetic Cralll-positi\-e Inhibits folic analogs Cantrisin, and Gram- ,lCid

Trimethoprim negative bacteria metabolism (anti-fobte)

Isoniazid (I\JH) synthetic A1yco/Jl1cferilllll Inhibits tll/Jerculosis mycolic acid

synthesis; analog of pyridoxine (Vit

Chemical class Examples

para-Jlllinosa licylic acid (PAS)

Biological source

synthetic


Spectrum (effective against)

Myco/)!lctcrilllli fu/)crclIlosis

Mode of action

86)

Anti-fol'lte

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Complexity of Antimicrobial Therapy

Drug Retention Problems

Eliminati 0 n from Host, Inactivation by Host

WrongDrug .... Wrong Spectrum ,..

of Activity (illfonred be,! guo,,),

Few Targets on Patha gen (fungi, protozoa, viruses)

~ Drug Delivery .., Problems Oral (destruction or poor uptake),

Inttavenous or Intramuscular (inconvenient), Topical,

Poor Ti ssue Uptake, Inj ection into Body Cavity

__ Side Effects Toxicity to Host,

Allergic Reaction, Normal Flora Disruption

( superinfection)

Selective Toxicity and Successnd Delivery

Development of .... Resistance ,..

Evasion, Mutation-Mediated,

TOXUlS

Exotoxins, Endotoxins

Acquired(R plasmids) • (in Gram-negative septicemia antibiotic treatment can even

.. make situation worse) Prevent Resistanc e b y Using: 1r.""""''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''Il

Only as Necessary, At sufficiently high doses

for suffi ci entl y Ion g p eri 0 d s, In Combination

Prevention of Growth Bactericidal,

B a cteri 0 stati c, Host Defenses

(elimination of pathogen from body)

Figure 2.2 Complexity of antimicrobial therapy [Lorian and Victor 2005]

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Drug resistance

The scope of the drug resistance problem

Bacteria clearly have a wondrous array of biochemical and

genetic systems for ensuring the evolution and dissemination of

antibiotic resistance [Medeiros 1997].

Drug resistant bacteria have been posing a major challenge to

the effective control of bacterial infections for quite some time.

Drug resistance refers to a situation in which the drugs that

usually destroy the bacteria no longer do so. It implies that

people can no longer be effectively treated against the bacteria.

Consequently, they are ill for longer periods of time; and they

face a greater risk of dying. Furthermore, epidemics are

prolonged, putting more people at a risk of becoming infected.

Antibiotic resistance is an extremely expensive problem. Its

costs in the US alone are estimated at US $5-$24 billion per year

[McGowan, Jr 2001].

Causes for drug resistance

,., One of the main causes of antibiotics drug resistance IS

antibiotic overuse, abuse, and in some cases, misuse, due

to incorrect diagnosis [Okeke et. AI. 1999].

,., A second cause is counterfeit drugs. Antibiotic use 111

animal husbandry is also creating some drug resistant

bacteria, which can be transmitted to humans [WHO 2002,

Feinman 1998].

,., Increased globalisation could also cause the spread of

drug resistance [MacPherson et. al. 2009].

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'r Finally, hospital settings often gIve rise to antibiotic

resistant bacteria [Weinstein 2001].

Natural (intrinsic) and acquired resistance

Antibiotic resistance can be divided into natural resistance and

acquired resistance. Natural resistance means that the bacteria

are 'intrinsically' resistant. For example, Streptomyces has some

genes responsible for resistance to its own antibiotic or

vancomycin resistance 111 Escherichia coli. Other examples

include organisms that lack a transport system or a target for

the antibiotics. In other cases, the resistance can be due to

increased efflux activity.

Acquired resistance refers to bacteria that are usually sensitive

to antibiotics, but are liable to develop resistance. Acquired

resistance is due to mutations in chromosomal genes, or by the

acquisition of mobile genetic elements, such as plasmids

[Gascoyne-Binzi 1994] or transposons [Grubb 1998], which carry

the antibiotic resistance genes

Genetic and phenotypic resistance

Broadly speaking, antibiotic resistance could also be divided

into genetic drug resistance, which is the one most commonly

discussed, and phenotypic drug resistance, which is a more

subtle type [Streiche et. al. 2004]. Genetic resistance is due to

chromosomal mutations or acquisition of antibiotic resistance

genes on plasm ids or transposons. Phenotypic resistance is due

to changes in the bacterial physiological state, such as the

stationary phase, antibiotic persisters [Balaban et. al. 2004], and

the dormant state.

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Genetic drug resistance mechanisms

Until the 1950s, it was not clear how the bacteria acquire drug

resistance. Then, Joshua Lederberg devised replica plating, and

demonstrated that the antibiotic resistant mutants are pre

existing [Hughes and Datta 1983]. Thus, the antibiotics merely

selected these mutants. Then, in 1988, John Cairns showed that

when the bacteria are not growing, they are nevertheless able to

acquire new mutations, due to some genetic alteration process.

The introduction of streptomycin for treating tuberculosis was

thwarted by the rapid development of resistance by mutation of

the target genes. Mutation is now recognized as the commonest

mechanism of resistance development 111 Mycobacterium

tuberculosis, and the molecular nature of the mutations

conferring resistance to most antituberculosis drugs is now

known [Musser 1995]. Those mutations are called adaptive

mutations. It was never formally proven that adaptive

mutations cause antibiotic resistance; however, it is possible,

particularly in non-growing forms of bacteria.

As the evolutionary time frame has to be less than 50 years it is

not possible to derive a model in which evolution could have

occurred by mutation alone from common ancestral genes. They

must have been derived from a large and diverse gene pool

presumably already occurring in environmental bacteria. Many

bacteria and fungi that prod uce antibiotics possess resistance

determinants that are similar to those found in clinical bacteria.

[Davies 1997]. Gene exchange might occur in soil or, more

likely, in the gut of humans or animals [Davies 1997]. It has

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been discovered that commercial antibiotic preparations contain

DNA from the producing organism, and antibiotic resistance

gene sequences can be identified by the polymerase chain

reaction. [Webb and Davies 1993].

There are five major mechanisms of antibiotic drug resistance,

which are due to chromosomal mutations:

,. Reduced permeability or uptake.

,.. Enhanced efflux.

,. Enzymatic inactivation.

',. Alteration or over-expression of the drug target.

,. Loss of enzymes involved in drug activation.

Efflux purrp

Antibiotic

Antibiotic

Fig 2.3 Four major biochemical mechanisms of antibiotic

resistance [To dar 2008J

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Multi-drug resistance (MDR) resistance

The multi-drug resistance mechanism can be caused by

different mechanisms in different organisms. For example, in

1959, the Japanese found Shigella species that were resistant to

Su Ifonamides, Streptomycin, Chloramphenicol, & Tetracycline.

The resistancewas due to plasmid, which carried different

antibiotic resistance genes [Hughes and Datta (1983)]. The other

MDR mechanism IS due to sequential accumulation of

chromosomal mutations in different drug resistant genes, as 111

the case of MDR- TB and XDR-TB

Examples of chromosomal mutations

Let us now examine some examples of chromosomal mutations.

A. Decreased uptake

Antibiotic modification is the best known: the resistant bacteria

retain the same sensitive target as antibiotic sensitive strains,

but the antibiotic is prevented from reaching it. This happens,

for example, with ~ lactamases-the ~ lactamase enzymatically

cleaves the four membered ~ lactam ring, rendering the

antibiotic inactive. Over 200 types of ~ lactamase have been

described. Most ~ lactamases act to some degree against both

penicillins and cephalosporins; others are more

specific-namely, cephalosporinases

enzyme found in Ellterobacter spp)

(for example, AmpC

or penicillinases (for

example, Staphylococcus allreus penicillinase). ~ Lactamases are

widespread among many bacterial species (both Gram positive

and Gram negative) and exhibit varY1l1g degrees of inhibition

2S


by P lactamase inhibitors, such as clavulanic acid [Livermore

1995].

Neisseria gonorrhoea porin can acquire mutations that can cause

resistance to penicillin and tetracycline [Davies 1997]. Another

example is Enicro/lacier aerogcllcs porin, which can acqUlre

mutations that cause cephalosporin resistance.

B. Increased efflux activity

Some antibiotic resistant bacteria protect the target of antibiotic

action by preventing the antibiotic from entering the cell or

pumping it out faster than it can flow in (rather like a bilge

pump in a boat). P Lactam antibiotics in Gram negative bacteria

gain access to the cell that depends on the antibiotic, through a

water filled hollow membrane protein known as a porin. In the

case of imipenem resistant Pseudolllollas aerugillosa, lack of the

specific D2 porin confers resistance, as imipenem cannot

penetrate the cell. This mechanism is also seen with low level

resistance to fluoroquinolones and aminoglycosides. Increased

efflux via an energy-requiring transport pump is a well

recognized mechanism for resistance to tetracyclines and is

encoded by a wide range of related genes, such as tet(A), that

have become distribu ted in the enterobacteriaceae. [Chopra,

Hawkey et. al. 1992].

Tetracycline efflux was discovered in the early 1980s. TetK

serves as an example for an efflux-mediated Tetracycline

resistance [Chopra, Hawkey et. al. 1992]. Under normal

conditions, the efflux gene, TetK, is not expressed, due to a

suppressor that is bound to the promoter region. However, in

26


the presence of Tetracycline, it binds to the repressor, relieves

the suppression, and causes transcription and translation of the

efflux pump, thereby leading to Tetracycline resistance.

C. Enzymatic inactivation

Antibiotic modification is the best known: the resistant bacteria

retain the same sensitive target as antibiotic sensitive strains,

but the antibiotic is prevented from reaching it. This happens,

for example, with ~ lactamases-the ~ lactamase enzymatically

cleaves the four membered ~lactam nng, rendering the

antibiotic inactive. Over 200 types of ~ lactamase have been

described. Most ~ lactamases act to some degree against both

penicillins and cephalosporins; others are more

specific-namely, cephalosporinases (for example, AmpC

enzyme found lt1 Elllero/Jaclcr spp. or penicillinases (for

example, Staphylococclis aureus penicillinase). ~ Lactamases are

widespread among many bacterial species (both Gram positive

and Gram negative) and exhibit varying degrees of inhibition

by ~ lactamase inhibitors, such as clavulanic acid [Livermore

1995].

D. Alteration of drug target / production of an alternative Target

Another mechanism by which bacteria may protect themselves

from antibiotics is the production of an alternative target

(usually an enzyme) that is resistant to inhibition by the

antibiotic while continuing to produce the original sensitive

target. This allows bacteria to survive in the face of selection:

the alternative enzyme "bypasses" the effect of the antibiotic.

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The best known example of this mechanism is probably the

alternative penicillin binding protein (PBP2a), which IS

produced in addition to the "normal" penicillin binding proteins

by methicillin resistant Stllphylococcus IllireliS (MRSA). The

protein is encoded by the mecA gene, and because PBP2a is not

inhibited by antibiotics such as flucloxacillin the cell continues

to synthesize peptidoglycan and hence has a structurally sound

cell wall. [Michel and Gutmann 1997]. The appearance III

1987 of vancomyclll resistant enterococci has aroused much

interest because the genes involved can be transferred to S

aureus, and this can thus theoretically result in a vancomycin

resistant MRSA. The mechanism also represents a variant of the

alternative target mechanism of resistance [Leclercq and

Courvalin 1997]. In enterococci sensitive to vancomycin the

normal target of vancomycin is a cell wall precursor that

contains a penta peptide that has a D-alanine-D-alanine

terminus, to which the vancomycin binds, preventing further

cell wall synthesis. If an enterococcus acquires the vanA gene

cluster, however, it can now make an alternative cell wall

precursor ending in D-alanine-D-Iactate, to which vancomycin

does not bind.

Most strains of Streptococcus PllCll1llOlllilC are highly susceptible

to both penicillins and cephalosporins but can acquire DNA

from other bacteria, which changes the enzyme so that they

develop a low affinity for penicillins and hence become

resistant to inhibition by penicillins [Tomasz and Munoz 1995].

The altered enzyme still synthesize peptidoglycan but it now

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has a different structure [Garcia-Bustos and Tomasz 1990].

Mutants of Streptococclis pyogencs that are resistant to penicillin

and express altered penicillin binding proteins can be selected

in the laboratory, but they have not been seen in patients,

possibly because the cell wall can no longer bind the anti

phagocytic M protein.

E. Loss of enzymes in drug activation

The loss of enzymes involved in drug activation is a relativelv

new mechanism of drug resistance. In this case, the antibiotic

itself is a prodrug, which has no direct activity against the

bacteria. Rather, it relies on the activation by a bacterial

enzyme. INH can serve as a useful example. KatG (catalase

peroxidase) [Heym et. al. 1992] is an enzyme involved in the

activation of INH, which produces a range of reactive

metabolites including reactive oxygen species and then reactive

organic radicals, which then inhibit multiple targets, including

mycolic acid synthesis [Yu et. al. 2003]. Another example is the

metronidazole (MTZ) prod rug. MTZ is activated through RdxA

(nitroreductase), and then forms reactive species that damage

the DNA. Thus, mutations in this enzyme cause resistance to

Metronidazole [Sisson et. al. 2002].

Regulation of resistance genes

Bacteria are extremely versatile 111 becoming resistant to

antibiotics, and are actually able to regulate their drug

resistance genes. One example is due to repressors, as in the

case of tetracycline, efflux mediated drug resistance (discussed

earlier) [Chopra and Hawkey et. al. 1992]. A second example,

29


which relates to erythromycin resistance genes (erm) is due to

attenuation [Bozdogan et. a!. 2004]. In the absence of

erythromycin, a stem-loop structure forms in the mRNA, which

buries the Ribosome Binding Site (RBS) and the start codon.

Thus, in the absence of the antibiotics, the drug resistance gene

is not expressed. However, low concentrations of erythromycin

cause the RBS and start codon to be exposed, causing a

translation of the drug resistance gene, erm, resulting in the

expression the gene.

Transfer of resistance genes

In addition to chromosomal mutations, a second broad category

of drug resistance is due to mobile genetic elements, such as

plasmids or transposons, which carry drug resistant genes. Few

examples are:

Streptomycin-resistance genes, strA- and strB, which can be

carried on plasmid, and cause Streptomycin resistant [Hughes

and Datta 1983].

Sulfa drug resistance, caused by plasmids that carry the drug

insensitive form of the enzyme [Wise and Abou-Donia (1975)].

A relatively new mechanism is the plasmid-mediated qnr

(quinolone resistance). The qllr gene encodes a device called

pentapeptide, which is a DNA mimic. Penta peptide binds to the

DNA gyrase and thus helps prevent the quinolone drug from

binding to the gyrase, thereby ca Llsing low-level resistance

[Tran and Jacoby 2002].

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Transposons can also carry drug resistant genes [Gascoyne

Binzi 1994]. It is noteworthy that plasmids and transposons are

not involved in drug resistance mechanisms in TB.

Phenotypic drug resistance

Phenotypic drug resistance refers to the fact that when the

bacteria are not growing, they can become unsusceptible to

antibiotics [Bronstad 1996]. Then, when the bacteria are sub

cultured into a fresh media, and they begin to grow again, they

regain their antibiotic susceptibility [Streiche, et. al. 2004]. This

complex mechanism has been posing significant problems as in

biofilm infections and particularly for TB chemotherapy.

BiofiIm infections

Bacteria that adhere to implanted medical devices or damaged

tissue can encase themselves 111 a hydrated matrix of

polysaccharide and protein, and form a slimy layer known as a

biofilm.

Biofilms have been found to be involved in a wide variety of

microbial infections in the body, by one estimate 80% of all

infections [NIH 2002]. Infectious processes in which biofilms

have been implicated include common problems such

as unnary

infections,

tract infections, ca theter infections, middle-ear

formation of dental plaque, gingivitis,

coating contact lenses [Rogers 2008], and less common hut more

lethal processes such as endocarditis, infections in cystic

fibrosis, and infections of permanent indwelling devices such as

joint prostheses and heart valves [Lewis 2001, Parsek and Singh

31


2003]. More recently, it has been noted that bacterial biofilms

may impair cutaneous wound healing and reduce topical

antibacterial efficiency 111 healing or treating infected skin

wounds [Davis et. al. 2008].

Microbial biofilms not only serve as a nidus for disease but also

are often associated with high-level antimicrobial resistance, a

consistent phenomenon that may explain the persistence of

many infections in the face of appropriate antimicrobial therapy

[Donlan 2002, Schachter 2003].

The mechanisms of resistance in biofilms are different from the

now familiar plasmids, transposons, and mutations that confer

innate resistance to individual bacterial cells. In biofilms,

resistance seems to depend on multicellular strategies [Stewart

and Costerton 2001].

Characterizing the antibiotic resistance of biofilms as "tenacious

survival rather than aggressive virulence", Stewart and

Costerton made four hypotheses:

, the drug fails to penetrate beyond the biofilm surface

layer;

, some bacteria differentiate into a protective phenotypic

state;

, antibiotic action IS antagonized within the regions of

nutrient depletion or waste production.

,. fourth mechanism, referred to as persistence. Persistence

has been seen, for example, in PseudollloIJas aerllgiIJosa,

where increased expression of the regulatory gene PvrR,

32


which keeps the bacteria in biofilms, renders them

insensitive to a wide range of different antibiotics

For example, some orthopaedic devices can have StaphylococcliS

al/reliS and Staphylococcus epidermidis infections. Once these

devices are infected with the biofilm, it is extremely difficult to

eliminate the biofilm completely merely by using antibiotics.

Often, the orthopaedic device must be replaced [Stewart

and Cos terton 2001].

Biofilm formation

Initially, the bacteria simply attaches to surfaces irreversibly,

and then irreversibly. Thus, early biofilms are formed, and turn

into mature biofilms. Such biofilms are able to release new

organisms off the structure. Biofilm bacteria are extremely

resistant to antibiotics. When the susceptibility of the

planktonic form and biofilm, is compared, it is observed that

antibiotic imipenem can destroy planktonic organisms of

Pseudomollas aerugillosa effectively at 1 (pg/ml), but require at

least 1024 (pg/ml) to fight against biofilm [Cornel is 2008].

The Biofilm structure is extremely complex. The bacteria are

divided into different SUb-populations, ranging from an almost

spore-like sub-population, to a more actively metabolizing

population at the colony surface.

Salicylate-induced antibiotic resistance

Another form of phenotypic drug resistance IS mediated by

salicylic acid, which is the active component in aspirin.

Different organisms have been found to have salicylate-

33


mediated drug resistance. Escherichia coli is the best example,

and additional ones include Klebsiella, Pseudomonas,

BurkllOlderia, and also MycolJt7cteriulII tuberculosis. It has been

demonstrated that in the presence of salicylate, TB bacteria is

less susceptible to INH, Rifampicin, EMB, and PAS. Preliminary

experiments in the mouse model of TB demonstrate that aspirin

can antagonize the activity of INH, indicating that it might also

have some effect in-vivo.

The mechanism of Salicylate-induced antibiotic resistance III

Escherichia coli is as follows:

Multiple Antibiotics Resistance (MAR) operon in the Escherichia

coli where the MarR is the repressor. Salicylate binds to MarR in

order to release the suppression of the MarAB operon. MarA

encodes a transcription factor, which in turn, activates the

transcription of the efflux pump acrAB, as well as the

membrane channel tolC, which is required for the functioning

of the pump. Thus, the first drug resistance mechanism IS

conducted through increased efflux [Cohen et. al. 1993].

In a second mechanism, MarA enhances the transcription of

micF, an antisense RNA for ompF, a membrane porin required

for entry of antibiotics. Thus, micF shuts down the expression

of ompF through antisense. When the porin expression is

reduced, the drug intake is reduced as well [Price et. al. 2000].

Bacterial persisters

The bacterial persisters are an important example of the

phenotypic resistance. Persistence was first discovered with

34


penicillin in 1944. Joseph Bigger demonstrated that penicillin

can kill merely 99% of the bacteria. The remaining 1 % of the

bacteria were persisters. When these persisters were cui tu red to

fresh media, they regained susceptibility to antibiotics [Balaban

et. al. 2004, Klingenberg 2007].

Toxin-Antitoxin (T A) model

For many years, the mechanism of persisted resistance to

antibiotics remained unknown. Then, in the 1980s, Harris

Moyed found the HipA gene being involved in persistence in

E.coli. Later, a group headed by Kim Lewis discovered that

HipA and HipB form a toxin antitoxin (TA) module, in which

an inappropriate expressIOn of toxin leads to persister

formation. The TA model was initially discovered on plasmids,

but was later observed in chromosomes of Illany bacterial

species. When a toxin is expressed, it shuts down transcription

and translation. Thus, the activity of toxins and anti-toxins

must be carefully regulated, to prevent cells from dying

[Schumacher et. al. 2009].

The model has difficulties explaining persistence in orgal1Isms

that do not have TA modules. More recently, a Chicago group

has demonstrated that if any toxic proteins are expressed, they

can induce persister formation, regardless of the toxin-antitoxin

module. These findings raise some questions as to the validity

of the toxin-antitoxin theory.

35


PhoU

Recently, we have identified a new persisted gene, PhoU,

through a transposon-based screen in Escherichia coli. The PhoU

mutant displays high susceptibility to a range of different

antibiotics, such as ampicillin, streptomycin, sulfa drugs, and

quinolone drugs [Li and Zhang 2007]. It is also more susceptible

to different conditions, such as heat, starvation, acid pH, and

weak acids. A wild type PhoU gene can complement PhoU

mutant phenotypes.

An interesting feature of the PhoU mutant is that it is highly

susceptible to ampicillin in the stationary phase. Many other

antibiotics, especially penicillin, are not active against

stationary phase bacteria, but merely against growing bacteria.

We have also demonstrated, through microarray experiments,

that the PhoU mutant has a hyperactive metabolism.

Thus, PhoU appears to be a suppressor mechanism for cellular

metabolism. When it is expressed, it shuts down cellular

metabolism. Although the detailed mechanism is not clear yet,

it is believed that PhoU could be an interesting drug target for

killing persister bacteria [Smith and Romesberg 2007].

Managing the drug resistance problem

Limiting the Spread of Drug Resistant Bacteria

Several measures could be used to prevent the spread of drug

resistant bacteria [O'Fallon et. al. 2009]:

36


Jy the use of better treatment strategies; better immunization

programmes; improved hygiene and nutrition; and

initiatives targeting the poor populations.

Jy it might be useful to establish antibiotic resistance

surveillance programmes.

,. better education of health care professionals is required to

prevent the prescription of unnecessary antibiotics.

,. It is noteworthy that significant investment of time, effort,

and money is necessary in order to control antibiotic

resistant bacteria. Of course, as long as antibiotics are

used, antibiotics resistance is bound to occur. However, it

IS possible to reduce the drug resistance problem

[O'Fallon et. a1. 2009]:

Jy to ensure that antibiotics are used only when necessary.

,.. to ensure that they are used for the appropriate amount of

time; that is, that the treatment is not stopped before it is

completed. Patient compliance is a key problem in that

respect.

,.. strategy for limiting drug resistance is to use antibiotics

combinations.

Unfortunately, while all these strategies seem sound 111 theory,

in reality, the problem persists.

Development of new antibiotics

Another possibility is to develop new antibiotics. However, that

is not an easy task. The sad irony is that many pharmaceutical

37


compal1les have decided to abandon their antibiotic

development programmes when new antibiotics are needed

most, since 99% of the drug candidates fail, and antibiotics are

not as profitable as other, more commonly used, drugs. The

traditional approach of screening microbes for antibiotics is not

efficient [Silver and Bostian 1993].

A second approach, which utilizes target-based screel1lng,

became popular when genomlcs tools became available.

However, although the idea is appealing, in reality, it is

extremely difficult. Many companies have tried this approach,

and so far they have all failed. The whole organism-based

approach is more feasible but the conditions of screen need

careful consideration [The Lancet 2009].

Mobilization of host defense mechanisms

Yet another approach is to mobilize host defense mechanisms.

This can be achieved through the mobilization of innate

immunity such as defensins, or through the development of

vaccines, which make antibiotics less necessary. The idea is to

boast the immune response capability to control the bacterial

infection. Of course, that approach is not always successful.

The use of normal bacterial flora

Finally, one could also potentially use normal bacterial flora to

suppress some pathogens.

Conclusion

To quote the Nobel Prize laureate Joshua Lederberg: "Antibiotic

resistance as a phenomenon is, in itself, not surprising. Nor is it

38


new. It is, however, newly worrying, because it is accumulating

and accelerating, while the world's tools for combating it

decrease in power and number."

This description may sound gloomy, but unfortunately, it is

rather precise. One must remember that the bugs have been on

this planet much longer than the human race and can develop

resistance to any antibiotics used to treat them. Hence, one has

to use a combination of approaches as discussed above to

mll1lmlZe the resistance problem, and hopefully can live 111

peace with the microbes.

39


Nosocomial (leU) Infection

CDC and NNIS system

The Centers for Disease Control and Prevention (CDC's)

National Nosocomial Infections Surveillance (NNIS) system has

been serving as an aggregating institution for 30 years. The

NNIS system is a voluntary, hospital-based reporting system

established to monitor hospital-acquired infections and guide

the prevention efforts of infection control practitioners. Patients

in intensive-care units (ICUs) are at high risk for nosocomial

infections and since 1987 have been monitored in the NNIS

system by site-specific, risk-adjusted infection rates according

to ICU type [Garner 1996].

Definitions of nosocomial infection

The NNIS System defines a nosocomial infection as a localized

or systemic condition

,.. that results from an adverse reaction to the presence of an

infectious agent(s) or to its toxin(s) and

,.. that was not present or incubating at the time of

admission to the hospital For the most nosocomial

infections, this means that the infection becomes usually

evident 48 hours (i.e., the typical incubation period) or

more after after admission.

However, because the incubation period varies with the type of

pathogen and to some extent with the patient's underlying

40


conditions, each infections must be assessed individually for

evidence that links it to the hospitalization [Garner 1996].

According to another definition, it states that nosocomial

infections are those infections that are the result of treatment in

a hospital or a healthcare service unit. Infections are considered

nosocomial if they first appear 48 hours or more after hospital

admission or within 30 days after discharge This type of

infection is also known as a hospital-acquired infection (or, in

generic terms, healthcare-associated infection) [Eggimann &

Pi ttet 2001].

In the United States, the Centers for Disease Control and

Prevention estimates that roughly 1.7 million hospital

associated infections, from all types of bacteria combined, cause

or contribute to 99,000 deaths each year [Pollack 2010].

The connection between the high death rate of hospitalized

patients and the exposure of patients to infectious

microorganisms was first made in the mid-nineteenth century.

Hungarian physician Ignaz Semmelweis (1818-1865) noted the

high rate of death from puerperal fever in women who

delivered babies at the Vienna General Hospital. At about the

same time, the British surgeon Joseph Lister (1827-1912) also

recognized the importance of hygienic conditions in the

operating theatre. His use of phenolic solutions as sprays over

surgical wounds helped lessen the spread of microorganisms

resident in the hospital to the patient. He recognized that

infections could be transferred from the surgeon to the patient.

41


Lister's actions spurred a series of steps over the next century,

which has culminated in today's observance of sterile or near

sterile conditions in the operating theatre [Ruef 2005].

Nosocomial infections occur worldwide, both in the developed

and developing world. They are a significant burden to

patients and public health. They are a major cause of death and

increased morbidity in hospitalized patients. They may cause

increased functional disability and emotional stress and may

lead to conditions that reduce quality of life. Not only do they

affect the general health of patients, but they are also a huge

burden financially. The greatest contributors to these costs are

the increased stays tha t pa tien ts with nosocomial infections

require [Vincent et. al. 1995, Ruef 2005].

Nosocomial infections are most frequently infections of the

urinary tract, surgical wounds, and the lower respiratory tract.

A World Health Organization prevalence study and other

studies have shown that these infections most commonly occur

in intensive care units (ICUs) and in acute surgical and

orthopedic wards [Ruef 2005]. Infection rates are also higher in

patients with increased susceptibility due to old age,

underlying disease, or chemotherapy. They are susceptible to

infection because of their underlying diseases or conditions

associated with impaired immunity as well as several violations

of their immune system or risks of aseptic mistakes in patient

management during invasive monitoring and they are prone to

secondary infections after exposure to broad -spectrum

antimicrobials [Eggimann and Pittet 2001].

42


Factors that influence infection

Nosocomial infections, may be exogenous or endogenous in

origin. The exogenous source may be another person in hospital

(cross infection) or a contaminated item of equipment or

building service (environmental infection). A high proportion

of clinically apparent hospital infections endogenous (self

infection), the infecting organisms being derived from the

patient's own skin, gastro-intestinal or upper respiratory flora

[Ruef 2005, Benn 1985].

Most infections acquired III hospital are caused by

microorganisms that are commonly present as commensal in the

general population. Thus, contact with microorganisms is

seldom the sole or main event predisposing to infection, various

risk factors, alone or in combination, influence the frequency

and nature of hospital infection.

Susceptibility to infection

The National Nosocomial Infection Surveillance System

database compiled by the CDC shows that the risk factors that

increase the opportunity for hospitalized individuals to acquire

infections are:

'Y a prolonged hospital stay

, severity of underlying illness

,. compromised nutritional or immune status

'Y use of indwelling catheters

43

----------------------------------------------


,.. failure of health care workers to wash their hands

between patients or before procedures

,.. prevalence of antibiotic-resistant bacteria from the

overuse of antibiotics

Natural resistance to infection IS lower 111 infants and the

elderly, who often constitute the majority of hospital patients.

Preexisting disease, such as diabetes, or other conditions for

which the patient was admitted to hospital, and the medical or

surgical treatment, including immunosuppressive drugs,

radiotherapy or splenectomy, may also reduce the patient's

natural resistance to disease. Moreover, the natural defense

mechanisms of the body surfaces may be bypassed either by

injury or by procedures such as surgery, insertion of an

indwelling catheter, tracheotomy or ventilatory support

[Wenzel 1983].

Contact with other patients and staff

In common with large institution or workplace, the patients and

staff of a hospital share many facilities in close or crowded

conditions. Admitting infected patients or carriers for treatment

clearly serves as a potential source of infection of others.

Patients with comparable susceptibility to infection tend to be

concentrated in the same area, e.g. in neonatal units, burns

units or urological wards, where infected and non-infected

patients may be cared for by the same staff, thus creating

nu merous opportunities for the spread of microorganisms by

direct contact. The more susceptible patients usually require the

44


most intensive care with far more daily contacts with staff who

act as vectors in the transmission of microbes like insects

spreading parasites [Wenzel 2003].

Inanimate reservoirs of infection

Equipment and materials in use in hospitals often become

contaminated with microorganisms, which may subsequently

be transferred to susceptible body sites on patients.

Gram-positive cocci, derived from the body flora of the hospital

population, are found in the air, dust, and on surfaces where

they 111ay survive along with fungal and bacterial spores of

environmental origin.

Gram-negative aerobic bacilli are common in moist situations

and in fluids, where they often survive for long periods, and

may even multiply 111 the presence of minimal nutrients. An

important example of this is legionelle in hospital domestic

wa ter supplies.

Awareness of the common reservOirs of environmental and

contaminating hospital microorganisms provides the basis for

maintaining standards of hygiene (cleaning, disinfection,

sterilization) throughout the hospital as well as good

engineering and building [Ruef 2005].

Role of antibiotic treatment

At least 30% hospital patients receive antibiotics, and this exerts

strong selective pressure on the microbial flora, especially of

the gastrointestinal tract, leading to the development of

4S


antibiotic-associated diarrhoeas due to Clostridiulll difficile, one

of the commonest causes of outbreaks of hospital infection.

Sensitive species or strains of microorganisms which normally

maintain a protective function on the skin and other mucosal

surfaces tend to be eliminated, whereas those that are more

resistant survive and become endemic 111 the hospital

population [Ruef 2005]. This may restrict the range of agents

available for treatment and may lead to the transmission of

plasmid-mediated antimicrobic resistance into strains that show

increased virulence, survival and spread within the hospital

[Step han 2001].

Microorganisms causing hospital (leU) infection

Infection is a major cause of morbidity and mortality among

patients admitted in intensive care units (reUs). Each year,

health care associated infections affect an estimated two million

Americans, including 500,000 intensive care unit (ICU) patients,

resulting in an estimated 90,000 deaths and $4.5 billion 111

excess health care costs (NCID 2006). ICU patients are at

increased risk of acquiring infections, most of which are

associated with the use of invasive devices [Richards et al. 2000,

Benn 1985] such as:

:r Urinary tract infection associated with the use

of indwelling urinary catheters to drain the bladder [Saint

et. al. 2002].

46


.,. Bloodstream infections associated with the use of central

line catheters, inserted in about one-half of reu patients to

provide medication, nutrition, and fluids (O'Grady et. a!.

2002).

.,. Pneumonia associated with the use of mechanical

ventilators in patients requiring assisted breathing (Tablan

et. a!. 2004).

The most important microorganisms responsible for hospital

infection are listed in Table 2.2 [Ducel 2002]:

Table 2.2 Nosocomial Infections Due to Bacteria and Fungi in

ICU Patients

Infections

Bloodstream Infections (BSI)

Lower respiratory tract infection / Ventilator associated pneumonia (V AP)

Urinary Tract Infection (UTI)

Upper respiratory tract infection

Gastrointestinal,

Surgical-site infections (SSI)

Nosocomial etiologies

Coagulase-negative Staphylococci, Enterococci, Fungi, Candida, StaphlflococclIs allrCIIS, Escherichia coli, Klcbsiella spp., PSeUdOl/lOllaS spp.

S trep tococcus pnCU1/101I iac, Hacl/lOph i IllS inflllellzac, Klebsiella pneul/lOlIiae, Lcgiollclla pne1l1l1ophila, Mycoplasma, Chlalllydia, Pseudol/lOnas acrugil1osa, A ci IIctobacte r [mul/lIm i i, S taphyl ocoeCllS allrcus, MycobacteriulII tu/Jerculosis Gram-negative enterics, Eschericllia coli, Protells I'lIlgaris, PseudO/llonas spp. Klebsiella PIICUl/lOllial', Fungi, Enterococci, StrcptococCllS pyogcnes, MRSA, Fungi, Candida, Neisseria IIIcnillgitides Co njllcbacleri u III d i pll Illcriae. Escherichia coli, Bactcroides fragilis, Enterococci, Anaerobes SlapllljlocOCCllS allrCllS, Pselidolllollas spp. Coagulase -ve Staphlflococci, Enterococci, fungi, Enterobacter species, and Escherichia coli,

47

-_._-----


Routes of Transmission

The hospital offers many opportunities for the exchange of

microbes, many of which are harmless and a normal part of the

balance between man and his environment. For there to be

significant risk of infection, several factors including the right

susceptible host and the appropriate inocu lum of infecting

microorganisms, must be linked via an appropriate route of

transmission, Understanding of the sources and transmission

routes of hospital infection enables efforts to be concentrated in

more effective preventive measures [Ruef 2005, Damani 2003].

Common routes of transmission for different microorganisms

are shown in the Table 2.3.

Table 2.3 Main routes of transmission

Route

Contact transmission

Droplet transmission

Airborne transmission

Description

The most important and frequent mode of transmission of nosocomial infections.

Occurs when droplets are generated from the source person mainly during coughing, sneezing, and talking, and during the performance of certain procedures such as bronchoscopy. Transmission occurs when droplets containing germs from the infected person are propelled a short distance through the air and deposited on the host's body.

Occurs by dissemination of either airborne droplet nuclei (small-particle residue {S lIm or smaller in size} of evaporated droplets containing microorganisms that remain suspended in the air for long periods of time) or dust particles containing the infectious agent. Microorganisms carried in this manner can be dispersed widel\' bv air currents and may become inhaled by a

48

Route

Common vehicle transmission

Vector borne transmission


Description

susceptible host within the same room or over a longer distance from the source patient, depending on environmental factors; therefore, special air handling and ventilation are required to prevent airborne transmission. Microorganisms transmi tted by airborne transmission include Legiollcl/n, Mlicobncterilllll tuberculosis and the rubeola and varicella viruses.

Applies to microorganisms transmitted to the host by contaminated items such as food, water, medications, devices, and equipment.

Occurs when vectors such as mosquitoes, flies, rats, and other vermin transmit microorganisllls.

Contact transmission is divided into two subgroups: direct

contact transmission and indirect-contact transmission (Table

2.4)

Table 2.4 Routes of contact transmission

Route Description

Direct- Involves a direct body surface-to-body surface contact and contact physical transfer of microorganisllls between a susceptible transmissi host and an infected or colonized person, such as occurs when on a person turns a patient, gives a patient a bath, or performs

other patient-care activities that require direct personal contact. Direct-contact transmission also can occur between two patients, with one serving as the source of the infectious microorganisms and the other as a susceptible host.

Indirect- Involves contact of a susceptible host with a contaminated contact intermediate object, usually inanimate, such as contaminated transmissi instruments, needles, or dressings, or contaminated gloves on that are not changed between patients. In addition, the

improper use of saline flush syringes, vials, and bags has been implicated in disease transmission in the US, even when healthcare workers had access to gloves, disposable needles, intravenous devices, and flushes.

49


Self-infection and cross-infection

Self-infection may occur due to transfer into the wound of

staphylococci (or occasionally streptococci) carried in the

patient's nose and distributed over the skin, or of coliform

bacilli and anaerobes released from the bowel during surgery.

Alternatively, cross infection may result from staphylococci or

coliform bacilli derived from other patients or healthy staff

earners. The organisms may be transferred into the wound

during operation through the surgeon's punctured gloves or

moistened gown, on imperfectly sterilized surgical instruments

and materials or by air-borne theatre dust. Postoperatively,

organisms may be transferred in the ward from contaminated

bed-linen, by air-borne ward dust or in consequence of a faulty

wound dressing technique (Figure 2.2) [Damani 2003].

Self infection

Cross infection

Figure 2.4 Self and cross infection

50


Of all the possible routes, by far the most likely in this example

is self-infection from patient's own bowl flora and is therefore

against this route that most specific preventive measures in

colorectal surgery are directed. Understanding of possible

sources of infection and the methods available to block

transmission to susceptible sites forms the basis of hospital

infection control [Benn 1985, Ruef 2005].

Cross-infection is more often caused by 'hospital' strains

selected for characteristics of antimicrobial resistance and

virulence. An important example at present is MRSA, which can

be easily identified by the microbiology laboratory, which

should have a system for alerting the infection control team

who need to collect the following basic epidemiological data .

." patient details

r the si te and extent of infection

the dates of admission, operative procedures, first

recognition of infection 1255 15

specimens and laboratory isolates and typing results

ward and staff details.

The clustering of cases according to a common surgical team or

location in the ward may suggest a common source and may be

the first firm indication of an outbreak of hospital infection.

Soon after admission to hospital, individuals commonly become

contaminated with the 'hospital flora'. This has been shown

51


with Staphylococcus aureus in studies of patients before and

during hospital treatment. Patients who need to stay longer in

hospital, e.g. those requiring intensive care or the elderly are

less able to withstand infection and the risk of hospital infection

are greater [Weinstein 1998].

Prevention and control

The infection control policy

The establishment of an effective infection control organization

is the responsibility of good management of any hospital. There

will normally be two parts [Damani, 2003, Wenzel 2003]:

:>- The infection con trol committee is a m u I ti -discipl inary

group of individuals who meet to discuss current

surveillance data to formulate and update policies for the

whole hospital on matters having implications for

infection for infection control, and to manage outbreaks of

nosocomial infection [Wenzel 2003].

,. An infection control team of workers, which is headed by

the infection control doctor (usually the microbiologist),

to take day-to-day responsibility for this policy.

The function of this team include surveillance and control of

infection and monitoring of hygiene practices, advising the

infection control committee on matters of policy relating to the

prevention of infection and the education of all staff in the

microbiologically safe performance of procedures. The infection

control nurse is a key member of this team. Close working links

S2


between the microbiology laboratory, infection control nurse

and different clinical specialties and support services (including

sterile serVices, laundry, pharmacy and engineering) are

important to establish and maintain the infection control policy

and to ensure that it is rationally based on and that the

recommended procedures are practicable. Some of the control

measures 111 which the infection control team should be

involved are as follows [Wenzel 1997, Silvestr 1999, Wenzel

2003, Ruef 2005]

Sterilization

The provision of sterile instruments, dressings and fluids is of

fundamental importance in hospital practice. Sterilization by

heat in high-vacuum autoclaves has become accepted hospital

practice [Favero 1991].

The development of these sterilizers for processmg wrapped

goods facilitated the provision of a centralized service of sterile

supply to wards, complementing the existing theatre service.

The availability of a wide range of prepacked single-use items

(syringes, needles, catheters, and drainage bags) sterilized

commercially by g-irradiation or ethylene oxide has further

improved aseptic procedures and removed the need for

reprocessing items that are difficult to clean and therefore

impossible to sterilize [Wenzel 2003].

Most fluids for topical use or intravenous administration are

now prepared commercially or 111 regional units where

standards of quality control and efficiency for bulk processes

53


are more readily achieved than 111 individual hospital

pharmacies.

Aseptic Techniques

The provision of sterile equipments will not prevent the spread

of infection if there is carelessness in its usc. Wherever possible,

no touch techniques must be used, coupled with strict personal

hygiene on the part of the operator. These routines and may be

modified as required for other procedures such as wound

dressing and insertion of intravenous catheters [Favero 1991,

Wenzel 2003, Damani, 2003].

Cleaning and Disinfection

The general hospital environment can be kept in good order by

attention to basic cleaning, waste disposal and laundry. The use

of chemical disinfectants for walls, floors, and furniture is

necessary only in special instances, such as spillages of body

fluids from patients with blood-borne virus infections. Ward

equipments such as bedpan washer / disinfectors and

dishwashers should be monitored to ensure reliable

performance, and cleaning materials such as mop heads and

cloths should be heat disinfected and stored dry after use

[Favero 1991]. Pre-cleaning of contaminated instruments and

equipments, preferably by means of an automatic washing

process with an ultrasonicator, is an essential step before

disinfection or sterilization [Wenzel 2003, Damani, 2003].

54


Skin Disinfection and Antisepsis

The ease of acquisition and transfer of transient hospital

contaminants, particularly Gram-negative bacilli on the hands

of staff, is an important factor in the spread of hospital

infection. Thorough hand washing after any procedure

involving nursing care or close contact with the patient is

essential. Alcohol-based hand antiseptics or 'rubs' have been

introduced in wards where routine hand washing with water

and detergents is not practica ble [Damani, 2003]. Gloves may be

worn for dirty contact procedures, such as emptying a urinary

drainage bag or bed-pan, although it should not be forgotten

that the gloved hand may also become contaminated by

transient hospital flora.

Proced ures for pre-opera ti ve disinfection of the pa tient' s skin

and for surgical scrubs are mandatory within the operating

theatre. Dilute 'in-use' solutions of antiseptics may readily

become colonized with Gram-negative bacteria and should be

replaced regularly. Ideally, single-use preparations should be

used. Restriction should be placed on the indiscriminate use of

antiseptics and disinfectants by means of a disinfectant policy

agreed by pharmacists, microbiologists and key users, such as

theatre staff [Simmons 1990, Favero 1991].

Prophylactic antibiotics

Widespread and haphazard use of antibiotics hastens the

emergence of antibiotic-resistant bacteria, and increases both

the incidence of toxic side-effects and the cost of treatment.

55


However, rational antibiotic prophylaxis plays an important

role in infection control. Specific indications include peri

operative prophylaxis in gastrointestinal and gynecological

surgery directed predominantly against anaerobic infection and

for patients known to have bacteriuria at the time of urological

surgery or instrumentation, directed against the urine isolate.

An antibiotic policy which limits the choice of broad-spectrum

agents is important both for prophylaxis and treatment [Singh

2000].

Protective clothing

Different activities within the hospital require different degrees

of protection to staff and patients. In operating theatres wearing

of sterile gloves, headgear and face masks minimizes the

shedding of microorganisms. The properties of fabrics available

of theater use have improved, and now include close-weave

ventile fabrics that are comfortable to wear and allow

evaporation of moisture. 'Total protection' of operating site

may be considered for certain high-risk clean surgery such as

hip replacements, during which the surgical team may wear

exhaust-ventilated suits and operate under conditions of ultra

clean laminar air flow [Wenzel 2003, Bearman 2006].

For many ward procedures in which there may be soiling, or for

simple barrier nursing of patients with communicable diseases,

plastic aprons, and gloves are used. Gloves, face masks and

goggles are also indicated for specific procedures when dental

. ----------

56


procedures. These are sometimes referred to as 'universal

precautions.

Isolation

The isolation procedures should list facilities and procedures

needed to prevent the spread of specific infections to other

patients (source isolation) and to protect susceptible or

immunocompromized patients (protective isolation). Effective

isolation demands a highly disciplined approach by all staff to

ensure that none of the barriers to transmission (air-borne,

direct and indirect contact) are breached. are breached. Multi

bedded rooms may be used, and even wards converted during

hospital outbreaks, but the simplest solution wherever possible

is to use single rooms [Hospital Infection Control Practice

Advisory Committee 1996, Damani, 2003].

Cubicle isolation, by which the patient is nursed alone in a

room separated by a door and corridor from other patients,

confer a substantial measure of protection. Preferably, each

isolation room has its own toilet and washing facility. Clean,

filtered air is supplied to the room, which should be at negative

pressure (exhaust-ventilated) to the corridor for source isolation

or at positive pressure (pressure-ventilated) to the corridor, for

protective isolation. If, however, there is a small airlock

vestibule separating the room from the outer corridor, then

exhaust ventilation of the airlock will give effective isolation for

either situation. The vestibules or lobby should contain a wash

S7


basin and include space for gownmg and equipment [Wenzel

2003].

In some critical situations such as bone marrow transplantation

units, where air-borne contamination with environmental

fungal spores is a problem, the efficiency of air filtration may be

increased and laminar airflow maintained as a barrier around

the patient. Stringent isolation, such as plastic tent or 'Trexler'

isolator, is required only for patients with highly contagious

infections, such as those due to Lasa, Marburg and Ebola

viruses, who are nursed in a high-security isolation unit.

Hospital building and design

The routine maintenance of the hospital building is important,

ensurIng that surfaces wherever possible are smooth,

impervious and easy to clean. Major rebuilding works on or

near the hospital sites may generate dust containing fungal and

bacterial spores, with implications for specialized units serving

immunocompromized patients. Close communications with

works department and hospital administra tion are necessary to

co-ordinate any protective action. When a new hospital or

modification of existing building is planned, the infection

control team should be closely involved in discussing the plans.

In many countries, guidance on new building design exists to

minimize potential hospital-acquired infection. Areas requiring

special attention include operating theatres, kitchens, acute

wards, laboratories, and air-conditioning systems [Sakharkar

1998]. The risk of Legionnaires' disease is reduced by installing

58


water supplies that circulate below 20°C for the cold and above

60°C for the hot circuit.

Equipment

Any object or item for clinical use should be assessed to

determine the appropriate method, frequency and site of

decontamination. Wherever possible, heat processes are

preferred, although this may be precluded for certain thermo

labile items such as fiber-optic endoscopes [Damani, 2003].

Personnel

An occu pa tional heal th service in hospi ta Is shou I d screen staff

before employment and offer appropriate immunization.

Hepatitis B vaccine should be given to all health care workers.

Those at special risk performing exposure prone procedures,

such as invasive surgery, should be screened for blood-borne

vauses. All staff (including medical students) should receive

occupational health advice and protection [Damani 2003]. Staff

who have contracted specific infections such as diarrhoea or

following needles tick injury should report and be screened if

necessary [Wenzel 2003, Ruef 2005].

Monitoring

Routine microbiological monitoring of the equipments is of

little benefit, although monitoring of the physical performance

of air-conditioning plants and machinery used for disinfection

and sterilization is essential. In the event of an outbreak of

hospital infection, more specific monitoring targeted at the

S9


known or likely causative microorganism should be considered

[Ruef 2005].

Microbiological screening of staff or patients is not undertaken

routinely, but it may be needed for specific purposes: to detect

carriers of MRSA and hepatitis viruses in those performing

some types of surgery or where transmission to patients has

occurred.

Surveillance and the role of the laboratory

The detection and characterization of hospital infection

incidents or outbreaks relay on laboratory data that alert the

infection control team to unusual cluster of infection, or to the

sporadic appearance of organisms that may present a particular

infection risk or management problem. This is sometimes

referred to as the 'alert organism' system. Bacterial typing

schemes and antibiograms are very important in this regard.

Regular visits to wards are also important to record data on

infected patients for whom specimens have not been received

and to respond to problems as they occur. Such visits also serve

to provide opportunities for practical teaching, which is another

important element of the infection control team's responsibility

[Wenzel 2003, Damani, 2003, Ruef 2005].

Efficacy of Infection Control

The evidence base in the literature for acceptable proof of

efficacy of infection control measures is scant. These include

sterilization, hand-washing, closed-drainage systems for

unnary catheters, intravenous catheter care, peri-operative

60


antibiotic prohylaxis for contaminated wounds and techniques

for the care of equipment used in respiratory therapy. Isolation

techniques are assumed to be responsible as suggested by

experIence or inferences. Measures which are now considered

to be ineffective include the chemical disinfection of floors,

walls, sinks and routine environmental monitoring [Ruef 2005].

Effective surveillance and action by the infection control team

have been shown to reduce infection rates. One important role

of the team is to monitor compliance with practices known to be

effective and to eliminate the many rituals or less effective

practices which may even increase the incidence or cost of

cross-infection. As further advances occur in medical care and

limited health care resources are spread across hospital and

community needs, innovations in infection control will need to

be evaluated for efficacy and cost-effectiveness. With this

understanding it is possible that hospital infection can be

controlled and largely prevented. The dictum of Florence

Nightingale, made over a century ago, that 'the very first

requirement in a hospital is that it should do the sick no harm',

remains the goal [Wenzel 2003, Ruef 2005].

Summary

Hospitals should take a variety of steps to prevent nosocomial

infections, including [Damani 2003]:

.,.. Adopt an infection control program such as the one

sponsored by the U.s. Centers for Disease Control (CDC),

which includes quality control of procedures known to

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lead to infection, and a monitoring program to track

infection rates to see if they go up or down.

,.. Employ an infection control practitioner for every 200

beds.

>- Identify high-risk procedures and other possible sources

of infection.

>- Strict adherence to hand-washing rules by health care

workers and visitors to avoid passlllg infectious

microorganisms to or between hospitalized patients

>- Strict attention to aseptic (sterile) technique 111 the

performance of proced u res, inc! uding use of steri Ie

gowns, gloves, masks, and barriers

r Sterilization of all reusable equipment such as ventilators,

humidifiers, and any devices that come in contact with

the respiratory tract

>- Frequent changing of dressings for wounds and use of

antibacterial ointments under dressings

, Remove nasogastric (nose to stomach) and endotracheal

(mouth to stomach) tubes as soon as possible

, Use of an antibacterial-coated venous catheter that

destroys bacteria before they can get into the blood stream

, Prevent contact between respiratory secretions and health

care providers by using barriers and masks as needed

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, Use of silver alloy-coated unnary catheters that destroy

bacteria before they can migrate up into the bladder

r Limitations on the use and duration of high-risk

procedures such as urinary catheterization

" Isolation of patients with known infections

" Sterilization of medical instruments and equipment to

prevent contamination

" Reductions in the general use of antibiotics to encourage

better immune response in patients and reduce the

cultivation of resistant bacteria

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Intensive care unit (leU)

Introduction

An intensive care unit (TCU), critical care unit (CCU), intensive

therapy unit or intensive treatment unit (ITU) is a specialized

section of a hospital that provides comprehensive and

continuous care for persons who are critically ill and who can

benefit from treatment [Gupta et. al. 2007, Sakharkar 1998].

During the Crimean War In 1854, Florence Nightingale felt the

necessity to separate seriously wounded soldiers from less

seriously wounded was observed. Thus, Nightingale reduced

mortality from 40% to 2% on the battlefield, creating the

concept of intensive care.

In response to a polio epidemic (where many patients required

constant ventilation and surveillance), Bjorn Ibsen established

the first intensive care unit in Copenhagen in 1953 [Eggimann &

Pittet (2001)]. Dr. William Mosenthal, a surgeon at the

Dartmouth-Hitchcock Medical Center [Vincent, et al. (1995),

pioneered the first application of this idea in the United States.

In the 1960s, the importance of cardiac arrhythmias as a source

of morbidity and mortality 111 mvocardial infarctions (Heart

Attacks) was recognized.

Thus, the development of intensive care units made the care for

more seriously sick patients possible. It allowed utilizing more

technically oriented tools to monitor and get information

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instantly about any changes of the patient's physiological

parameters and developed new strategies to save life.

Purpose

The purpose of the intensive care unit (ICU) is simple even

though the practice is complex. Healthcare professionals who

work in the ICU provide around-the-clock intensive monitoring

and treatment of patients seven days a week. Patients are

generally admitted to an ICU if they are likely to benefit from

the level of care provided. Intensive care has been shown to

benefit patients who are severely ill and medically unstable

that is, they have a potentially life-threatening disease or

disorder (Figure 2.3).

Figure 2.5 A man recovering from quadruple bypass surgery

in an intensive care unit [Custom Medical Stock Photo].

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Although the criteria for admission to an reu are somewhat

controversial- excluding patients who are either too well or too

sick to benefi t from in tensi ve care - there are four

recommended priori ties that in tensi vists (clinicians who

specialize in critical illness care) use to decide this question.

These priorities include:

, Critically ill patients III a medically unstable state who

reqUIre an intensive level of care (monitoring and

treatment).

,. Patients requiring intensive monitoring who may also

require emergency interventions .

.,. Patients who are medically unstable or critically ill, and

who do not have much chance for recovery due to the

severity of their illness or traumatic injury.

, Patients who are generally not eligible for leu admission

because they are not expected to survive. Patients in this

fourth category require the approval of the director of the

reu program before ad mission.

Descri ption

reu care requires a multidisciplinary team that consists of but

IS not limited to intensivists; pharmacists and nurses;

respiratory care therapists; and other medical consultants from

a broad range of specialties including surgery, pediatrics, and

anesthesiology. The ideal reu will have a team representing as

many as 31 different health care professionals and practitioners

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-----------------


who assist in patient evaluation and treatment. The intensivist

will provide treatment management, diagnosis, interventions,

and individualized care for each patient recovering from severe

illness [Damani 2003].

ICUs are highly regulated departments, typically restricting or

limiting the number of visitors to the patient's immediate

family even during visiting hours. The patient usually has

several monitors attached to various parts of his or her body for

real-time evaluation of medical stability. The intensivist will

make periodic assessments of the patient's cardiac status,

breathing rate, urinary output, and blood levels for nutritional

and hormonal problems that may arise and require urgent

attention or treatment. Patients who are admitted to the rcu for

observation after surgery may have special requirements for

monitoring. These patients may have catheters placed to detect

hemodynamic (blood pressure) changes or require endotracheal

intubation to help their breathing, with the breathing tube

connected to a mechanical ventilator [Brilli et. al. 2001].

In addition to the intensivist's role in direct patient care, he or

she is usually the lead physician when multiple consultants are

involved 111 an intensive care program. The intensivist

coordinates the care provided by the consultants, which allows

for an integrated treatment approach to the patient.

Nursing care has an important role in an intensive care unit.

The nurse's role usually includes clinical assessment, diagnosis,

and an individualized plan of expected treatment outcomes for

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each patient (implementation of treatment and patient

evaluation of results). The rcu pharmacist evaluates all drug

therapy, including dosage, route of administration, and

monitoring for signs of allergic reactions. In addition to

checking and supervlslllg all levels of medication

administration, the ICU pharmacist is also responsible for

enteral and parenteral nutrition (tube feeding) for patients who

cannot eat on their own. rcus also have respiratory care

therapists with specialized training in cardiorespiratory (heart

and,-n(r1g) care for critically ill patients. Respiratory therapists ~ .....

generally provide medications to help patients breathe as well

as' the care and support of mechanical ventilators. Respiratory

therapists also evaluate all respiratory therapy procedures to

maximize efficiency and cost-effectiveness.

Large medical centers may have more than one ICU. These

specialized intensive care units typically include a CCU

(coronary care unit); a pediatric ICU (PICU, dedicated to the

treatment of critically ill children); a newborn ICU or NICU, for

the care of premature and critically ill infants; and a surgical

ICU (SICU, dedicated to the treatment of postoperative

patients).

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