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Chapter 9 – Controlling Microbial Growth in the Environment Basic
1
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 Sterilization: Kills and destroys all forms of microbial life including viruses
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 Antisepsis: Reducing number of microorganisms and viruses by applying chemicals to living
tissue
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 Sanitization: Disinfecting places and utensils (door handle) to minimize chances of disease
transmission
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2
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–cidal control agents on microbial growth
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Define microbial death rate and describe its significance in microbial control
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4
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 When cell walls are disrupted, it can no longer hold when in hypotonic solution (water
moves in)
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 Extreme chemicals, temperature, or pH causes the 3D shape of proteins to denature
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5
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 The nature of the sites to be treated
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 The environmental (pH and temp
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 As for the living, Bacterial endospores are most resistant (Examples: Bacillus and Clostridium
endospores)
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Discuss environmental conditions that can influence the effectiveness of antimicrobial agents
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 pH: Low pH, or acidic conditions help enhance the effect of disinfectants
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8
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 Moist Heat in a Autoclave
o Advantages are water is a better conductor than dry heat and it is relatively fast
within 15 minutes
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 Dry Heat in an Oven
o Advantages are its better for powders and oils that can’t be boiled or steamed
o Disadvantages are it requires ~16 hours (at the same temperature of autoclave)

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 Method 1: After autoclaving sample on a tape, if no growth, original material is considered
sterile
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 This puts endospores (in small vial) in contact with sample
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This means it’s sterile
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What is Pasteurization? What are the three different pasteurization methods?
 Pasteurization prevents the spoilage of beverages by heating microbes (not sterilization)
 Batch method: 30 min at 63°C
 Flash pasteurization: (mostly used today) 15 seconds at 72°C, destroys all pathogens
 Ultra-high-temperature pasteurization: 135°C for 1 sec; consumer claims taste changes
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i
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i
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Compare and contrast dessication and lyophilization
 Dessication is drying all water so microbes cannot grow
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 Lyophilization combines freezing liquid nitrogen or frozen CO2 and drying H2O with a
vacuum to preserve
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Describe the use of filters for disinfection and sterilization
 Filters sterilizes heat sensitive materials like vaccines, enzymes, antibiotics, and some
culture media
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 Microbiologists estimate the number of microbes in a fluid by counting the number
deposited on the filter
 High-efficiency particulate air (HEPA) filters are used in operating rooms to remove bacteria
from air

14
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Fungi less affected
than bacteria
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Differentiate ionizing radiation from non-ionizing radiation as they relate to microbial control
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energize electrons to free and attack other atoms, creating ions
ii
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iii
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form pyrimidine dimers in DNA, inhibiting transcription; used best to disinfect air or
clear fluids



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