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Kenneth S. Destura, RMT

ISOLATION OF PURE CULTUREOF ORGANISM & INHIBITION

AND DESTRUCTION OF

MICROORGANISMS

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Isolation of PureCulture of Organism

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ISOLATION OF PURECULTURE

COLONIES

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SERIAL DILUTIONPOUR PLATE

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SERIAL DILUTIONPOUR PLATE

Nutrient Agar

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SERIAL DILUTIONPOUR PLATE

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SERIAL DILUTIONPOUR PLATE

Quebec ColonyCounter

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SERIAL DILUTIONPOUR PLATE

Formula:

Number of bacteria/mL = colony count x reciprocal of

dilution

Number of colonies/plate = Ave. no. of colonies in 5

squares x 62.5

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STREAK PLATE METHOD

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STREAK PLATE METHOD

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STREAK PLATE METHOD

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STREAK PLATE METHOD

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Inhibition & Destructionof Microorganisms

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Inhibition and Destruction ofMicroorganisms

Definitions

Sterilization process whereby all forms of microbiallife, including bacterial spores are killed

Disinfection process whereby pathogenicorganisms but not necessarily all microorganisms orspores are destroyed

Antiseptic disinfectants used on living tissues

Biocides also known as chemical sterilants, theseare chemicals used to destroy all life

Disinfectants chemical sterilants used for shorterperiods

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Inhibition and Destruction ofMicroorganisms

Definitions

Thermal death point lowest temperature at whichall organisms in a liquid suspension can be killed in

10 minutes Thermal death time minimal length of time in which

all bacteria in a liquid suspension will be killed at agiven temperature

-cide - a suffix indicating that the agent will kill thekind of organism in question (e.g. viricide)

-static - a suffix indicating that the agent will preventthe growth of the type of organism in question (e.g.,

bacteriostatic)

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Inhibition and Destruction ofMicroorganisms

Factors influencing antimicrobial activity:

the concentration and kind of a chemical agent used;

the intensity and nature of a physical agent used;

the length of exposure to the agent;

the temperature at which the agent is used;

the number of microorganisms present;

the organism itself; and the nature of the material bearing the microorganism.

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Physical Agents

Heat

Moist heat

Autoclave

Boiling

Tyndallization

Pasteurization

Inspissation

Dry heat Hot air Sterilization

Incineration

Radiation

Ionizing

Non-ionizing

Filtration

Freezing

Deep Freezing

Lyophilization Ultrasound vibrations

Lasers

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Chemical Agents

QUATERNARY AMMONIUM COMPOUNDS -cationic detergentsused as disinfectants for food utensils and small instruments, andbecause of low toxicity, as antiseptics for skin; act by disruptingbiological membranes and possibly by denaturing proteins.

ALDEHYDES -reactive molecules that can be used as chemicalsterilants; may irritate the skin; act by combining with proteins andinactivating them

STERILIZING GASES (e.g., ethylene oxide, betapropio-lactone) -

can be used to sterilize heat-sensitive materials such as plasticpetri dishes and disposable syringes; act by combining withproteins and inactivating them. Recently, vapor-phase hydrogenperoxide has been used to decontaminate biological safety cabinet