Page 30 - MNU-PM502- Pharmaeutical Microbiology Theoritical Book

Pharm D- Clinical Pharmacy Program Third Level Pharmaceutical Microbiology& Antimicrobials (PM 502)

• Another name is ‘fractional
sterilization’ A fraction is sterilized each

day due to the use of repeating heat.

• After each heating, the resting period will
allow spores that have survived to

germinate into bacterial cells; these cells
will be killed by the next day's heating.

• Uses: helpful in sterilizing food and

(heat labile media)

➢ Food
➢ sugar-containing media,
➢ gelatin-containing media.

3- At temperature above 100˚C

(Steam under pressure)

Principle: Water boils when its vapor pressure equals the pressure of the
surrounding atmosphere

• This occurs at 100˚C for normal atmospheric pressure

• Thus, when water is boiled within a closed vessel at increased pressure, the
atmosphere at which it boils and that of the steam it forms will rise above 100˚C

Steam is an effective sterilant for two reasons

➢ Saturated steam is an extremely effective carrier of thermal energy, many
times more effective than is hot (dry) air
➢ Any resistant, protective outer layer of the microorganisms can be softened

by the steam, allowing coagulation of the sensitive inner portions of the

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