START-HERE Ch07 Lecture

7/31/2019 START-HERE Ch07 Lecture

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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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Copyright 2010 Pearson Education, Inc.

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



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Sterilization : Removing all microbial lifeCommercial sterilization : Killing C. botulinum endosporesDisinfection : Removing pathogensAntisepsis : Removing pathogens from living tissue


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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


8/55Copyright 2010 Pearson Education, Inc.Table 7.2

Population Death Rate Is Constant


9/55Copyright 2010 Pearson Education, Inc.Figure 7.1a

A Microbial Death Curve



Effectiveness of Treatment

Depends onNumber of microbesEnvironment (organic matter, temperature, biofilms)Time of exposure

Microbial characteristics


11/55Copyright 2010 Pearson Education, Inc.Figure 7.1b

A Microbial Death Curve



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



7-3 Describe the effects of microbial control agentson cellular structures.

Actions of Microbial Control Agents

Learning Objective



Actions of Microbial Control Agents

Alteration of membrane permeabilityDamage to proteinsDamage to nucleic acids



Check Your UnderstandingWould a chemical microbial control agent thataffects plasma membranes affect humans? 7-3



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



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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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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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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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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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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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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Microbial Characteristics

Endospores and Mycobacteria


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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

START-HERE Ch07 Lecture

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