2010 chap08 controlling microbial growth student

8/8/2019 2010 Chap08 Controlling Microbial Growth Student

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Controlling Microbial Growthchapter 8

Destroy pathogens and prevent

their transmission

Reduce or eliminate microorganismsfrom water, food and othersubstances


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Control Terms

Sterilization

Disinfection

Sanitization reduction of microbial population to safelevel

Antisepsis reduction of microbial population on livingtissue

Chemotherapy use of chemical agents to kill orinhibit growth of microorganisms within host tissue

Cidal

Static


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Patterns of Microbial Death

microorganisms are not killed instantly

population death usually occursexponentially

microorganisms were previouslyconsidered to be dead when they did notreproduce in conditions that normallysupported their reproduction


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Tab. 8.1


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Fig. 8.2


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Conditions influencing how effective

antimicrobials agents will be.


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Catagories of Control

Physical methods

Chemical methods

Mechanical methods Biological methods


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1) PHYSICAL Control

Physical agents


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Moist Heat Sterilization

must be carried out above 100oCwhich requires saturated steamunder pressure

carried out using an autoclave


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Ex: The Autoclave orSteam Sterilizer


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Pasteurization

controlled heating at temperatureswell below boiling

used for milk, beer and otherbeverages

process does not sterilize but doeskill pathogens present


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Dry Heat Sterilization

less effective than moist heatsterilization, requiring highertemperatures and longer exposuretimes items subjected to 160-170oC for 2 to 3

hours


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Dry Heat Incineration

bench topincinerators areused to sterilize

inoculating loopsused inmicrobiologylaboratories


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Measuring Heat-Killing Efficiency

thermal death time (TDT)

shortest time needed to kill all microorganismsin a suspension at a specific temperature and

under defined conditions

decimal reduction time (D or D value)

time required to kill 90% of microorganisms orspores in a sample at a specific temperature


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Example:

Zvalue


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Low Temperatures

freezing stops microbial reproduction due to

lack of liquid water

some microorganisms killed by icecrystal

refrigeration


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Filtration

depth filtersthickfibrousorgranularfiltersthatremove

microorganismsbyphysical

membranefiltersporousmembraneswith definedporesizes

thatremovemicroorganismsprimarilyby


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Filtering air

surgical masks

cotton plugs onculture vessels

high-efficiencyparticulate air(HEPA) filters


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Radiation


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Ultraviolet (UV) Radiation

- limited to surfacesterilization

because it does notpenetrate glass, dirtfilms, water, andother substances

-


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Ionizing Radiation

penetrates deep into objects

destroys bacterial endospores;


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2) Chemical Control

Chemical agents

Phenolics

Alcohols Halogens

Heavy metals

Quaternary ammonium compounds

Aldehydes Gases


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Phenolics

Antiseptic and disinfectant

Denature proteins and disrupt membranes

Effective in the presence of organic material


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Alcohols

Antisepticanddisinfectant

Most widelyused

Denatureproteins / dissolvemembranes

Bactericidal / fungicidal


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Halogens

One of fivecompounds:

Fluorine, chlorine,bromine, iodineand astitine

Disinfectants (F,Cl, Br)

Antiseptic (I)


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Heavy metals

Germicides: mercury, silver,arsenic, zinc, copper

Combine with proteins anddeactivate them


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Quartenary Ammonium compounds

QAC detergents

Amphipathic


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Aldehydes

Formaldehyde, glutaraldehyde

Sporicidal and can be used as chemicalsterilants

Highly reactive molecules


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Effects of Glutaraldehyde


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Sterilizing gases

Ethylene oxide gases

Very strong alkylating agent

sterilization

Microbicidal, sporicidal


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Chemotherapeutic Agents

chemicals that can be used internally tokill or inhibit the growth of microbeswithin host cells

their selective toxicity allows them totarget the microbe without harming thehost


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3) MECHANICAL Control

Filtration

High pressure washing


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4) Biological Control

Natural control processes

Bacteriophage


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Determining the effectiveness of

antimicrobial agents

complex process regulated byfederal agencies

EnvironmentalProtection

Agency (E

PA)

Food and Drug Administration (FDA)

Health Canada Canada


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Phenol coefficient test

2010 chap08 controlling microbial growth student

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