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Medical Microbiology
Chapter 10
Sterilization, Disinfection,
and Antisepsis
Control of Microbial Growth
Historical perspective of the control of
microbial growth
Civil War, etc.
Terminology
Sterilization - process of killing all microbes
there is no such thing as “almost sterile”
Disinfection - process of killing most
microbes
especially pathogens
disinfectant - a physical or chemical agent
that kills pathogens
this term usually implies use on inanimate
objects
Terminology (cont.)
Antisepsis – use of chemical agents on skin or
other living tissues to eliminate or limit
microbial growth
Antiseptic
Sanitizer - a disinfectant used on food-handling
equipment (eating utensils, etc.)
Germicide or Bactericide - agent that kills
bacteria
Bacteriostatic agent - a substance that inhibits
the growth of bacteria, but does not kill them
The Rate of Microbial Death
Microorganisms are not killed instantly by
physical or chemical agents, like heat and
disinfectants
Only a fraction of the total population are
killed in a given amount of time
Mechanism of Action
How do things like heat and disinfectants kill
bacteria?
Injury to the plasma membrane
How would this kill a bacterial cell?
Damage to Proteins
effect?
Damage to Nucleic Acids
effect?
Physical Methods
Moist heat - steam under pressure is the
most efficient sterilizing agent
Autoclaving
Boiling water - kills all vegetative cells
within a few minutes
Physical Methods (cont.)
Pasteurization –
63°C for 30 min
72°C for 15 sec
Time and temp.
There is a fairly new method of sterilizing milk and
other liquids so they don’t need to be refrigerated
Ultra High Temperature (UHT) treatment
140°C for 3 sec
Physical Methods (cont.)
Dry heat - takes longer and/or higher
temperatures than moist heat to kill
microbes
Why?
Flaming
Dry heat oven - 160-170°C for 1-2 hours
used for materials that would be damaged
by steam
powders, special wraps and dressings, some
glassware
Physical Methods (cont.)
Low Temperature - not a method of
sterilization, but does inhibit the growth of
many microbes
refrigeration, freezing, etc.
Filtering - used for air and materials that
would be damaged by heat (some drugs,
etc.)
HEPA filters, etc. (won’t catch viruses)
Physical Methods (cont.)
Radiation - “transmission of energy through
space”
causes mutations in DNA and possibly affects
enzyme function
ionizing radiation - x-rays and gamma rays
very powerful and damaging
used on spices, syringes, catheters, etc.
UV radiation - used in rooms, lab hoods, etc.
Chemical Methods
Ethylene Oxide Gas – common for tubing,
instruments, etc.
Aldehydes – formaldehyde, formalin
(embalming), glutaraldehyde
Hydrogen peroxide
Halogens: Iodine (Iodophors) and Chlorine
(Bleach)
Alcohols (ethanol and isopropanol)
Chlorhexidine and Triclosan (soaps and
detergents)