multi drug resistance molecular pathogenesis
TRANSCRIPT
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MULTI DRUG RESISTANCE
By: ALAGAR . S M.Tech /
COMPUTATIONAL BIOLOGY
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Objectives
• What is antimicrobial resistance
• Why antibacterial resistance is a concern
• How antibacterials work
• Mechanisms of resistance to antibacterials
• Indian scenario
• NDM-1
• Factors responsible for Resistance
• Alternate & Trending approaches
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Introduction
• Throughout history there has been a continual battle between human beings and multitude of micro-organisms that cause infection and disease
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In his 1945 Nobel Prize lecture, Fleming himself warned ofthe danger of resistance –
“It is not difficult to make microbes resistant topenicillin in the laboratory by exposing them toconcentrations not sufficient to kill them, and thesame thing has occasionally happened in the body……and by exposing his microbes to non-lethalquantities of the drug make them resistant.”
History Nobel Lecture, December 11, 1945
Sir Alexander Fleming
The Nobel Prize in Physiology or Medicine 1945
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Timeline of Antibiotic Resistance
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Why resistance is a concern
• Resistant organisms lead to treatment failure
• Increased mortality
• Resistant bacteria may spread in Community
• Low level resistance can go undetected
• Added burden on healthcare costs
• Threatens to return to pre-antibiotic era
• Selection pressure
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Drug resistance occurs in :
BACTERIA—ANTIBIOTIC RESISTANCE Endoparasites Viruses—Resistance to antiviral drugs Fungi Cancer cells
Drug Resistance
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What is Multi Drug Resistance
MDROs are microorganisms, predominantly bacteria, that are resistant to one or more classes of antimicrobial agents
Examples of MDROs Methicillin-resistant staphylococcus aureus (MRSA)
Vancomycin-intermediate staphylococcus aureus (VISA)
Vancomycin-resistant staphylococus aureus (VRSA)
Vancomycin-resistant enterococcus (VRE)
Streptococcus pneumoniae resistant to penicillin and other broad-spectrum agents
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• The concentration of drug at the site ofinfection must inhibit the organism and alsoremain below the level that is toxic to humancells.
GOODMAN & GILMAN'S THE PHARMACOLOGICAL BASIS OF THERAPEUTICS - 11th Ed. (2006)
Antibiotic Resistance
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Antibiotic Resistance
Defined as micro-organisms that are not
inhibited by usually achievable systemic
concentration of an antimicrobial agent with
normal dosage schedule and / or fall in the
minimum inhibitory concentration (MIC)
range.Antibiotic Resistance (DR)
= MIC / MCC > Toxic Plasma Concentration
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Mechanisms of action of antibiotics
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Mechanism Antibiotic Resistance
Intrinsic (Natural) Acquired
Genetic Methods
Chromosomal Methods Mutations
Extra chromosomal Methods Plasmids
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Antibiotic Resistance
Some microorganisms may ‘born’ resistant,
some ‘achieve’ resistance by mutation or some
have resistance ‘thrust upon them’ by plasmids
Some are born great, some achieve greatness
or some have greatness thrust upon them
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Intrinsic Resistance
1. Lack target :
• No cell wall; innately resistant to penicillin
2. Innate efflux pumps:
• Drug blocked from entering cell or ↑ exportof drug (does not achieve adequate internalconcentration). Eg. E. coli, P. aeruginosa
3. Drug inactivation:
• Cephalosporinase in Klebsiella
It occurs naturally.
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Acquired resistance
Mutations
• It refers to the change in DNA structure of the gene.
• Occurs at a frequency of one per ten million cells.
• Eg.Mycobacterium.tuberculosis,Mycobacteriumlepra , MRSA.
• Often mutants have reduced susceptibility
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Plasmids
• Extra chromosomal genetic elements can replicateindependently and freely in cytoplasm.
• Plasmids which carry genes resistant ( r-genes) are called R-plasmids.
• These r-genes can be readily transferred from one R-plasmid toanother plasmid or to chromosome.
• Much of the drug resistance encountered in clinical practice isplasmid mediated
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Mechanisms of Resistance Gene Transfer
• Transfer of r-genes from one bacterium toanother
Conjugation
Transduction
Transformation
• Transfer of r-genes between plasmids within the bacterium
By transposons
By Integrons
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Transfer of r-genes from one bacterium to another
Conjugation : Main mechanism for spread of resistance
The conjugative plasmids make a connecting tubebetween the 2 bacteria through which plasmid itselfcan pass.
Transduction : Less common method
The plasmid DNA enclosed in a bacteriophage is transferred to another bacterium of same species. Seen in Staphylococci , Streptococci
Transformation : least clinical problem.
Free DNA is picked up from the environment (i.e..From a cell belonging to closely related or same strain.
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Mechanisms of Resistance Gene Transfer Transposons
Transposons are sequences of DNAthat can move around differentpositions within the genome of singlecell.
The donor plasmid containing theTransposons, co-integrate with acceptorplasmid. They can replicate duringcointegration
Both plasmids then separate and eachcontains the r-gene carrying thetransposon.
Eg ; Staphylococci,Enterococci
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Mechanisms of Resistance Gene Transfer
Integrons
Integron is a large mobile DNAcan spread Multidrug resistance
Each Integron is packed withmultiple gene casettes, eachconsisting of a resistance geneattached to a small recognition site.
These genes encode severalbacterial functions includingresistance and virulence.
They cannot promote self transfer
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Biochemical mechanisms of antibioticresistance
• Prevention of drug accumulation in the bacterium
• Modification/protection of the target site
• Use of alternative pathways for metabolic / growth requirements
• By producing an enzyme that inactivates the antibiotic
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Decreased permeability: Porin Loss
Interior of organism
Cell wall
Porin channel
into organism
Antibiotic
Antibiotics normally enter bacterial cells via porin channels
in the cell wall
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Decreased permeability: Porin Loss
Interior of organism
Cell wall
New porin channel
into organism
Antibiotic
New porin channels in the bacterial cell wall do not allow
antibiotics to enter the cells
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ATP Binding Cassette
Multidrug and toxic compound exporter
Small multidrug resistance transporters
Resistance-nodulation-division
Major facilitator superfamily
Efflux pumps
• Cytoplasmic membrane transport proteins.
• Major mechanism for resistance in Tetracyclines.
• Some gram -ve bacteria inhibit the plasmidmediated synthesis of porin channels ,whichobstructs the influx of hydrophilic Penicillinseg.ampicillin
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Structurally modified antibiotic target site
Interior of organism
Cell wall
Target siteBinding
Antibiotic
Antibiotics normally bind to specific binding proteins on the
bacterial cell surface
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Structurally modified antibiotic target site
Interior of organism
Cell wall
Modified target site
Antibiotic
Changed site: blocked binding
Antibiotics are no longer able to bind to modified binding proteins
on the bacterial cell surface
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Modification/Protection of the Target site
Resistance resulting from altered target sites :
Target sites Resistant Antibiotics
Ribosomal point mutation Tetracyclines,Macrolides, Clindamycin
Altered DNA gyrase Fluoroquinolones
Modified penicillin binding proteins (Strepto.pneumonia)
Penicillins
Mutation in DNA dependant RNA polymerase (M.tuberculosis)
Rifampicin
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Antibiotic inactivation
Interior of organism
Cell wall
Antibiotic
Target siteBindingEnzyme
Inactivating enzymes target antibiotics
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Antibiotic inactivation
Interior of organism
Cell wall
Antibiotic
Target siteBindingEnzyme
Enzyme
binding
Enzymes bind to antibiotic molecules
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Antibiotic inactivation
Interior of organism
Cell wall
Antibiotic
Target siteEnzyme
Antibiotic
destroyedAntibiotic altered,
binding prevented
Enzymes destroy antibiotics or prevent binding to target sites
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By producing enzymes that inactivates antibiotic
a)Inactivation of b-lactam antibiotics•S. aureus, N. gonorrohoea, H.influenza, Produce b-lactamase which cleaves -lactam ring
b)Inactivation of Chloramphenicol• Inactivated by chloramphenicol acetyltransferase .• Gram-ve (enzyme present constitutively hence higherresistance) gram +ve bacteria (enzyme is inducible )
c)Inactivation of Aminoglycosides• Inactivated by acetyl, phospho & adenylyl transferasesPresent in gram +ve and gram –ve .
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Use of alternative pathways for metabolic / growth
requirements
• Resistance can also occur by alternate pathway that bypasses the reaction inhibited by the antibiotic.
• Sulfonamide resistance can occur from overproduction of PABA
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Drug Mechanism of resistance
Pencillins & Cephalosporiins
B Lactamase cleavage of the Blactam ring
Aminoglycosides Modification by phosphorylating, adenylatingand acetylating enzymes
Chloramphenicol Modification by acetylytion
Erythromycin Change in receptor by methylation of r RNA
Tetracycline Reduced uptake / increased export
SulfonamidesActive export out of the cell & reduced affinity of enzymes
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Indian scenario
• Lack of community awareness
• Availability over the counter
• Absence of central monitoring agency
• S. Pneumoniae fully resistant to cotrimoxazole
• Still sensitive to penicillins, macrolides and fluoroquinolones
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Enteric pathogens
• Vibrio cholerae :
– resistance to furazolidine, cotrimoxazole, nalidixicacid
– Tetracycline remains effective
• Coliforms
– ESBLs , extensive resistance to Beta lactumantibiotics
• Enteric fever
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STD
• Penicillin and fluoroquinolone resistance is widespread to gonorhhoea
• Alternate drugs like Azithromycin and cephalosporins should be used
• Syphilis still susceptible to Penicillins
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Gram positive Cocci
• Streptococci other than S. Pneumoniae
– Resistant to tetracycline and macrolides (40%)
– Still sensitive to penicillins
• Staph Aureus
– Methicillin resistance 50%-100%
– Vancomycin resistance also increasing
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Mycobacteria
• Multidrug resistance
– Combined resistance to rifampicin and isoniazid
• Extensively drug resistant TB
– Additional acquisition of resistance to a fluroquinolone and one of the three injectablesecond line drugs (capreomycin, kanamycin and amikacin)
• Steady rise in these patients
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What is NDM-1?
• NDM-1 stands for New Delhi metallo-beta-lactamase, an enzyme produced by certain strains of bacteria that have recently acquired the genetic ability to make this compound.
• The enzyme is active against other compounds that beta-lactam ring like penicillins, cephalosporins, and the carbapenems.
• bacteria that produce NDM-1 are resistant to all commonly used beta-lactam antibiotics, including carbapenems.
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New Delhi metallo-beta-lactamase Why everyone concerned ?
• There are currently no new drugs in the research pipelines that aim to stop NDM-1.To date, some strains of E.coli and Klebseilla pneumoniaeare known carriers of the gene, but the gene can be transmitted from one strain of bacteria to another through horizontal gene transfer.
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Naming the strain as New Delhi creates controversy
• The gene was named after New Delhi, the capital city of India, as it was first described by Yong et al. in 2009 in a Swedish national who fell ill with an antibiotic-resistant bacterial infection that he acquired in India . The infection was unsuccessfully treated in a New Delhi hospital and after the patient's repatriation to Sweden, a carbapenem-resistant Klebsiella pneumoniae strain bearing the novel gene was identified. The authors concluded that the new resistance mechanism "clearly arose in India, but there are few data arising from India to suggest how widespread it is."
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Treatment
• Many NDM-1 strains are resistant to all antibiotics except for colistin.
• Colistin is an older antibiotic that has not been used much in recent decades, because it is somewhat more toxic than other antibiotics.
• A few NDM-1 strains have been sensitive to tigecycline (Tygacil), but this agent should be used cautiously in serious infections because it does not achieve high levels in the bloodstream.
• A few strains have also been sensitive to aztreonam
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The spread of NDM-1 can be contained with
• The spread of NDM-1 within health-care facilities can be curbed through strict infection-control measures, including patient isolation and hand washing.
..
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Strategy to Contain Resistance
• Develop new antibiotics
–Bypass the drug resistance
• Judicious use of the existing antibiotics:
–Containment of drug resistance
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New Antibiotic Development
• Only 15 antibiotics of 167 under development had a new mechanism of action with the potential to combat of multidrug resistance.
• Lack of incentive for companies to develop antibiotics.
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Phage therapy
• Phage Therapy is the therapeutic use of lytic bacteriophages totreat pathogenic bacteria infections
• Bacteriophages are viruses that invade bacterial cells anddisrupt bacterial metabolism and cause the bacterium to lyse.
• Bacteriophage therapy is an important alternative to antibiotics
• The success rate was 80–95% with few gastrointestinal orallergic side effects. British studies also demonstrated significantefficacy of phages against Escherichia coli, Acinetobacter spp.,Pseudomonas spp and Staphylococcus aureus.
Alternate Approaches
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Quorum sensing
• Microbes communicate with each other and exchange signaling chemicals (Autoinducers)
• These autoinducers allow bacterial population to coordinate gene expression for virulence, conjugation, apoptosis, mobility and resistance
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Why named quorum sensing
• Single autoinducer from single microbe is incapable of inducing any such change
• But when its colony reaches a critical density (quorum), threshold of autoinduction is reached and gene expression starts
• QS signal molecules AHL, AIP, AI-2 & AI-3 have been identified in Gm-ve bacteria
• AI-2 QS –system is shared by GM+ve bacteria also
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WHY INHIBIT QUORUM SENSING
Proved to be very potent method for bacterial virulence inhibition.
Several QS inhibitors molecules has been synthesized which include AHL, AIP, and AI-2 analogues
QS inhibitors have been synthesized and have been isolated from several natural extracts such as garlic extract.
QS inhibitors have shown to be potent virulence inhibitor both in in-vitro and in-vivo,using infection animal models.
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Factors of Antibiotic Resistance
Environmental Factors
Drug Related Factors
Patient Related Factors
Prescriber Related Factors
Antibiotic Resistance
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• Huge populations and overcrowding
• Rapid spread by better transport facility
• Poor sanitation
• Increases community acquired resistance
• Ineffective infection control program
• Widespread use of antibiotics in animal husbandry
and agriculture and as medicated cleansing products
1. Environmental Factors
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• Over the counter availability of antimicrobials
• Counterfeit and substandard drug causing sub-optimal blood concentration
• Irrational fixed dose combination of antimicrobials
• Soaring use of antibiotics
2. Drug Related
Policy Decision at Higher level
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• Poor adherence of dosage Regimens
• Poverty
• Lack of sanitation concept
• Lack of education
• Self-medication
• Misconception
3. Patient Related
Patient Counseling, Awareness
Program
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Prescriber Related
• Inappropriate use of available drugs
• Increased empiric poly-antimicrobial use
• Overuse of antimicrobials
• Inadequate dosing
• Lack of current knowledge and training
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Poor Clinical Practice
• Poor clinical practice that fail to incorporate
the pharmacological properties of
antimicrobials amplify the speed of
development of drug resistance.
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Faulty Antibiotic Use
• Antimicrobials are over prescribed
• Available without prescription
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Over Prescribed Antibiotics
• Clinician should first determine whether antimicrobial therapy is warranted for a given patient
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Definitive Treatment
1. Can a narrower spectrum agent be substituted for initial empiric drug?
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Definitive Treatment (2)
1. Is one agent or combination of agents necessary?
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Examples
• -lactam + Aminoglycosides
• Extended spectum Penicillins + -lactamaseInhibitors
• Anti-tubercular regimen
• Anti-leprotic regimen
• Co-trimoxazole
• Sulphadoxin + pyrimethamine
• Artemisinin based Combination Therapy (ACT) in Malaria
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Definitive Treatment
What are the
– optimum dose,
– route of administration and
– duration of therapy?
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Definitive treatment
What specific test to identify patients who will not respond to treatment?
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Creating Super Bugs
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TRENDING APPROACHESNew Antibiotics – New bacteria
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Mutant Bacteriophages
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Quorum sensing
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