Control of Microbial Growth How to kill them once you grow them

Control of Control of Microbial GrowthMicrobial Growth

How to kill them once you How to kill them once you grow themgrow them

The Control of The Control of Microbial GrowthMicrobial Growth

Sepsis refers to microbial Sepsis refers to microbial contamination.contamination.

Asepsis is the absence of Asepsis is the absence of significant contamination.significant contamination.

Aseptic surgery techniques Aseptic surgery techniques prevent microbial prevent microbial contamination of wounds.contamination of wounds.

Sterilization: Removal of all microbial lifeSterilization: Removal of all microbial life Commercial Sterilization: Killing Commercial Sterilization: Killing C. botulinumC. botulinum

endosporesendospores Disinfection: Removal of pathogensDisinfection: Removal of pathogens Antisepsis: Removal of pathogens from living tissueAntisepsis: Removal of pathogens from living tissue Degerming: Removal of microbes from a limited Degerming: Removal of microbes from a limited

areaarea Sanitization: Lower microbial counts on eating Sanitization: Lower microbial counts on eating

utensilsutensils Biocide/Germicide: Kills microbesBiocide/Germicide: Kills microbes Bacteriostasis: Inhibiting, not killing, microbesBacteriostasis: Inhibiting, not killing, microbes

TerminologyTerminology

Filtration removes microbesFiltration removes microbes Low temperature inhibits microbial Low temperature inhibits microbial

growthgrowth RefrigerationRefrigeration Deep freezingDeep freezing LyophilizationLyophilization

High pressure denatures proteinsHigh pressure denatures proteins Desiccation prevents metabolismDesiccation prevents metabolism Osmotic pressure causes plasmolysisOsmotic pressure causes plasmolysis

Physical Methods of Physical Methods of Microbial ControlMicrobial Control

Filter SterilizationFilter Sterilization

Moist HeatMoist Heat

Radiation damages DNARadiation damages DNA Ionizing radiation (X rays, gamma rays, Ionizing radiation (X rays, gamma rays,

electron beams) electron beams) Nonionizing radiation Nonionizing radiation

UV UV Microwaves kill by heat; not especially Microwaves kill by heat; not especially

antimicrobialantimicrobial

Physical Methods of Physical Methods of Microbial ControlMicrobial Control

RadiationRadiation

Evaluating a disinfectantEvaluating a disinfectant Use-dilution testUse-dilution test

1. 1. Metal rings dipped in test bacteria Metal rings dipped in test bacteria are driedare dried

2. 2. Dried cultures placed in Dried cultures placed in disinfectant for 10 disinfectant for 10 min at 20°Cmin at 20°C

3. 3. Rings transferred to culture media Rings transferred to culture media to to determine whether determine whether bacteria survived bacteria survived treatmenttreatment

Chemical Methods of Chemical Methods of Microbial ControlMicrobial Control

ChemicalChemical Methods of Methods of Microbial ControlMicrobial Control

Figure 7.6

Evaluating a disinfectantEvaluating a disinfectant Disk-diffusion methodDisk-diffusion method

Types of DisinfectantsTypes of Disinfectants

Figure 7.7

Phenol Phenol Phenolics. LysolPhenolics. Lysol Bisphenols. Bisphenols.

HexachloropheneHexachlorophene, Triclosan, Triclosan Disrupt plasma Disrupt plasma

membranesmembranes

BiguanidesBiguanides ChlorhexidineChlorhexidine Disrupt plasma membranesDisrupt plasma membranes


Halogens. Iodine, ChlorineHalogens. Iodine, Chlorine Oxidizing agentsOxidizing agents Bleach is hypochlorous acid (HOCl)Bleach is hypochlorous acid (HOCl)



Table 7.6

AlcoholsAlcohols EthanolEthanol isopropanolisopropanol Denature Denature

proteins, proteins, dissolve lipidsdissolve lipids

Heavy Metals. Ag, Hg, CuHeavy Metals. Ag, Hg, Cu Oligodynamic actionOligodynamic action Denature proteinsDenature proteins


Surface-Active Agents or SurfactantsSurface-Active Agents or Surfactants


SoapSoap DegermingDegerming

Acid-anionic detergentsAcid-anionic detergents SanitizingSanitizing

Quarternary ammonium Quarternary ammonium compoundscompoundsCationic detergentsCationic detergents

Bactericidal, Denature Bactericidal, Denature proteins, disrupt plasma proteins, disrupt plasma membranemembrane

Chemical Food PreservativesChemical Food Preservatives Organic Acids Organic Acids

Inhibit metabolismInhibit metabolism Sorbic acid, benzoic acid, calcium propionateSorbic acid, benzoic acid, calcium propionate Control molds and bacteria in foods and Control molds and bacteria in foods and

cosmeticscosmetics Nitrite prevents endospore germinationNitrite prevents endospore germination Antibiotics. Nisin and natamycin prevent Antibiotics. Nisin and natamycin prevent

spoilage of cheesespoilage of cheese


AldehydesAldehydes Inactivate proteins by cross-linking with Inactivate proteins by cross-linking with

functional groups functional groups (–NH(–NH22, –OH, –COOH, —SH), –OH, –COOH, —SH)

Glutaraldehyde, formaldehydeGlutaraldehyde, formaldehyde


Gaseous SterilantsGaseous Sterilants Denature proteinsDenature proteins Ethylene oxideEthylene oxide


PeroxygensPeroxygens Oxidizing agentsOxidizing agents OO33, H, H22OO22, peracetic acid, peracetic acid


Microbial Microbial Characteristics and Characteristics and Microbial ControlMicrobial Control

Figure 7.11

Bacterial populations die at a constant Bacterial populations die at a constant logarithmic rate.logarithmic rate.

Figure 7.1a

Number of Number of microbesmicrobes

Environment Environment (organic (organic matter, matter, temperature, temperature, biofilms)biofilms)

Time of Time of exposureexposure

Microbial Microbial characteristiccharacteristicss

Effectiveness of antimicrobial Effectiveness of antimicrobial treatment depends on:treatment depends on:

Figure 7.1b

Microbial Microbial Characteristics and Characteristics and Microbial ControlMicrobial Control

Chemical Chemical agentagent Effectiveness againstEffectiveness against

EndosporesEndospores MycobacteriMycobacteriaa

PhenolicsPhenolics PoorPoor GoodGood

QuatsQuats NoneNone NoneNone

ChlorinesChlorines FairFair FairFair

AlcoholsAlcohols PoorPoor GoodGood

GlutaraldehydeGlutaraldehyde FairFair GoodGood

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Control of Microbial Growth How to kill them once you grow them