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Copyright 2010 Pearson Education, Inc.Lectures prepared by Christine L. Case
Chapter 7The Control of
Microbial Growth
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7-1 Define the following key terms related to microbialcontrol: sterilization, disinfection, antisepsis,degerming, sanitization, biocide, germicide,bacteriostasis, and asepsis.
The Terminology of Microbial Control
Learning Objective
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Sepsis refers to microbial contaminationAsepsis is the absence of significant contaminationAseptic surgery techniques prevent microbialcontamination of wounds
The Terminology of Microbial Control
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The Terminology of Microbial Control
Sterilization : Removing all microbial lifeCommercial sterilization : Killing C. botulinum endosporesDisinfection : Removing pathogensAntisepsis : Removing pathogens from living tissue
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The Terminology of Microbial Control
Degerming : Removing microbes from a limited areaSanitization : Lowering microbial counts on eatingutensilsBiocide/germicide : Kills microbesBacteriostasis : Inhibiting, not killing, microbes
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Check Your UnderstandingThe usual definition of sterilization is the removal ordestruction of all forms of microbial life; how couldthere be practical exceptions to this simpledefinition? 7-1
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7-2 Describe the patterns of microbial death causedby treatments with microbial control agents.
The Rate of Microbial Death
Learning Objective
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8/55Copyright 2010 Pearson Education, Inc.Table 7.2
Population Death Rate Is Constant
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9/55Copyright 2010 Pearson Education, Inc.Figure 7.1a
A Microbial Death Curve
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Effectiveness of Treatment
Depends onNumber of microbesEnvironment (organic matter, temperature, biofilms)Time of exposure
Microbial characteristics
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11/55Copyright 2010 Pearson Education, Inc.Figure 7.1b
A Microbial Death Curve
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Check Your UnderstandingHow is it possible that a solution containing a millionbacteria would take longer to sterilize than onecontaining a half-million bacteria? 7-2
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7-3 Describe the effects of microbial control agentson cellular structures.
Actions of Microbial Control Agents
Learning Objective
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Actions of Microbial Control Agents
Alteration of membrane permeabilityDamage to proteinsDamage to nucleic acids
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Check Your UnderstandingWould a chemical microbial control agent thataffects plasma membranes affect humans? 7-3
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Physical Methods of Microbial Control
7-4 Compare the effectiveness of moist heat (boiling,autoclaving, pasteurization) and dry heat.
7-5 Describe how filtration, low temperatures, highpressure, desiccation, and osmotic pressuresuppress microbial growth.
7-6 Explain how radiation kills cells.
Learning Objectives
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Heat
Thermal death point (TDP) : Lowest temperature atwhich all cells in a culture are killed in 10 minThermal death time (TDT) : Time during which allcells in a culture are killed
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Copyright 2010 Pearson Education, Inc.Table 7.2
Decimal Reduction Time (DRT)
Minutes to kill 90% of a population at a giventemperature
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Moist Heat Sterilization
Moist heat denatures proteinsAutoclave : Steam under pressure
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Copyright 2010 Pearson Education, Inc.Figure 7.2
An Autoclave
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Copyright 2010 Pearson Education, Inc.Figure 7.3
Steam Sterilization
Steam must contact items surface
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Pasteurization
Reduces spoilage organisms and pathogensEquivalent treatments
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C for 30 minHigh-temperature short-time : 72
C for 15 secUltra-high-temperature : 140 C for
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Hot-Air Autoclave
Equivalent Treatments 170C, 2 hr 121C, 15 min
Dry Heat Sterilization
Kills by oxidationDry heatFlamingIncineration
Hot-air sterilization
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Copyright 2010 Pearson Education, Inc.Figure 7.4
Filtration
HEPA removesmicrobes>0.3 m
Membranefiltration removesmicrobes>0.22 m
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Q&A
In what situation isfiltration the onlypractical way toeliminateundesirablemicrobes?
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Physical Methods of Microbial Control
Low temperature inhibits microbial growthRefrigerationDeep-freezingLyophilization
High pressure denatures proteinsDesiccation prevents metabolismOsmotic pressure causes plasmolysis
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Copyright 2010 Pearson Education, Inc.Figure 7.5
Radiation
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Radiation
Ionizing radiation (X rays, gamma rays, electronbeams)Ionizes water to release OH Damages DNA
Nonionizing radiation (UV, 260 nm)Damages DNA
Microwaves kill by heat; not especially antimicrobial
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Check Your UnderstandingHow is microbial growth in canned foods prevented? 7-4Why would a can of pork take longer to sterilize at a giventemperature than a can of soup that also contained pieces of
pork? 7-5 What is the connection between the killing effect of radiationand hydroxyl radical forms of oxygen? 7-6
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7-7 List the factors related to effective disinfection.7-8 Interpret the results of use-dilution tests and the
disk-diffusion method.
Chemical Methods of Microbial Control
Learning Objectives
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Principles of Effective Disinfection
Concentration of disinfectantOrganic matterpHTime
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Use-Dilution Test
Metal rings dipped in test bacteria are driedDried cultures are placed in disinfectant for 10 min at20
CRings are transferred to culture media to determinewhether bacteria survived treatment
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Copyright 2010 Pearson Education, Inc.Figure 7.6
Disk-Diffusion Method
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Copyright 2010 Pearson Education, Inc.Clinical Focus, p. 201
Clinical Focus
Which preparation is more effective?
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Check Your UnderstandingIf you wanted to disinfect a surface contaminated by vomitand a surface contaminated by a sneeze, why would yourchoice of disinfectant make a difference? 7-7
Which is more likely to be used in a medical clinic laboratory,a use-dilution test or a disk-diffusion test? 7-8
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7-9 Identify the methods of action and preferred uses ofchemical disinfectants.
7-10 Differentiate halogens used as antiseptics from halogens
used as disinfectants.7-11 Identify the appropriate uses for surface-active agents.7-12 List the advantages of glutaraldehyde over other chemical
disinfectants.
7-13 Identify chemical sterilizers.
Chemical Methods of Microbial Control
Learning Objectives
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Copyright 2010 Pearson Education, Inc.Figure 7.7a, b
Phenol & Phenolics
Disrupt plasma membranes
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Copyright 2010 Pearson Education, Inc.Figure 7.7c, d
Bisphenols
Hexacholorphene, triclosanDisrupt plasma membranes
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Biguanides
ChlorhexidineDisrupt plasma membranes
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Halogens
IodineTinctures : In aqueous alcoholIodophors : In organic moleculesAlter protein synthesis and membranes
ChlorineBleach: Hypochlorous acid (HOCl)Chloramine: Chlorine + ammoniaOxidizing agents
l h l
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Copyright 2010 Pearson Education, Inc.Table 7.6
Alcohols
Ethanol, isopropanolDenature proteins, dissolve lipidsRequire water
l
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Heavy Metals
Ag, Hg, and CuSilver nitrate may be used to prevent gonorrhealophthalmia neonatorumSilver sulfadiazine used as a topical cream on burns
Copper sulfate is an algicideOligodynamic action
Denature proteins
S f A i A S f
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Soap Degerming
Acid-anionic detergents Sanitizing
Quarternary ammoniumcompounds(cationic detergents)
Bactericidal, denature proteins,
disrupt plasma membrane
Surface-Active Agents, or Surfactants
Ch i l F d P i
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Chemical Food Preservatives
Organic acidsInhibit metabolismSorbic acid, benzoic acid, and calcium propionateControl molds and bacteria in foods and cosmetics
Nitrite prevents endospore germinationAntibiotics
Nisin and natamycin prevent spoilage of cheese
Ald h d
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Aldehydes
Inactivate proteins by cross-linking with functionalgroups ( NH2, OH, COOH, SH)Use: Medical equipment
Glutaraldehyde, formaldehyde, and ortho-phthalaldehyde
G S il
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Gaseous Sterilants
Denature proteinsUse: Heat-sensitive materialEthylene oxide
Pl
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Plasma
Free radicals destroy microbesUse: Tubular instruments
S iti l Fl id
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Supercritical Fluids
CO 2 with gaseous and liquid propertiesUse: Medical implants
P
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Peroxygens
Oxidizing agentsUse: Contaminated surfacesO3, H2O2, peracetic acid
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Check Your UnderstandingWhy is alcohol effective against some viruses andnot others? 7-9Is Betadine an antiseptic or a disinfectant when it is
used on skin? 7-10What characteristics make surface-active agentsattractive to the dairy industry? 7-11 What chemical disinfectants can be consideredsporicides? 7-12 What chemicals are used to sterilize? 7-13
Mi bi l Ch t i ti d Mi bi l
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7-14 Explain how the type of microbe affects thecontrol of microbial growth.
Microbial Characteristics and MicrobialControl
Learning Objective
Mi bi l Ch t i ti
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Copyright 2010 Pearson Education, Inc.Figure 7.11
Microbial Characteristics
Endospores and Mycobacteria
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Copyright 2010 Pearson Education, Inc.Table 7.7
Endospores and Mycobacteria
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Check Your UnderstandingThe presence or absence of endospores has an obviouseffect on microbial control, but why are gram-negativebacteria more resistant to chemical biocides than gram-positive bacteria? 7-14