Jacquelyn G. Black
Microbiology: Principles and
Explorations
Sixth Edition
Chapter 12:
Sterilization and Disinfection
Copyright © 2005 by John Wiley & Sons, Inc.
Principles of Sterilization and
Disinfection
• Disinfectant: Typically chemical agents
that are applied to inanimate objects
• Antiseptics: Typically chemical agents
that are applied to living tissues
• Table 12.1
• Sterilization: The killing or removal of
all living cells, viable spores, viruses in a
material or on an object
• Sterility: there are no living organisms
in or on an object
• Disinfection: The reduction of the
number of pathogenic microorganisms to
the point that they pose no danger of
disease
Disinfectant and Antiseptic Response of
Staphylococcus aureus
Disinfectant and Antiseptic Response of
Escherichia coli
Denaturing Proteins
Action of a Surfactant
Structural Formulas of Common
Disinfectants
Heavy Metal Effect on Bacterial Growth
Biodecontamination
Unit—Hydrogen
Peroxide
Biodecontamination
Unit—Ethylene
Oxide
Sterilization—Hot Air Oven
Small Countertop Autoclave
Model Autoclave
Ionizing Radiation
• X rays and gamma rays are forms of ionizing
radiation
• So named because it can dislodge electrons from
atoms creating ions
• Damages DNA and produces peroxides (powerful
oxidizing agents in cells)
• Deinococcus radiodurans: Able to survive 1000X
the amount of radiation that would kill a human
(bioremediation of radioactive contaminated sites)
Autoclaving
• If water is heated under pressure, its boiling point is
elevated, so temperatures above 100oC can be reached
• Pressure: 15 lbs per square inch (psi)
• 15 – 20 minutes at 121oC
• Prions are highly resistant and must be sterilized longer
and at higher temperature (134oC for 18 min)
Checking for Sterility
Pasteurization
• A process invented by Pasteur to destroy microbes
that caused wine to sour, does not achieve sterility
• Kills pathogens: Salmonella and Mycobacterium
• Milk is pasteurized by heating it to 71.6oC for at least
15 seconds (flash method)
• Milk is pasteurized by heating it to 62.9oC for 30
minutes (holding method)
Large Automatic Hospital Autoclave
Preservation
by Drying
Lyophilization—Stoppering Tray Dryer
Lyophilization—
Manifold Dryer
The Control of Microbial Growth
• A definite proportion of the organisms die in
a given time interval
• The fewer organisms present, the shorter the
time needed to achieve sterility
• Microorganisms differ in their susceptibility
to antimicrobial agents
• The most susceptible phase for most
organisms is the logarithmic growth phase
• Germicide: An agent capable of killing
pathogens and nonpathogens but not
necessarily endospores
• Bacteriostatic agent: An agent that
inhibits the growth of bacteria
1. Bactericide
2. Bacteriostatic
The Use of Physical Methods in Control
of Microbial Growth
• Heat and other physical agents are
normally used to control microbial
growth and sterilize objects:
1.
2.
3.
4.
Heat
Low Temperatures
Filtration
Radiation
Heat
• One of the most popular ways to destroy
microbes (flame or boiling)
• Moist or Dry heat may be used
• Exposure to boiling water for 10 minutes is
sufficient to destroy vegetative cells and
eukaryotic spores
• Steam sterilization (autoclaving) is necessary to
destroy the bacterial endospore
Radiation
• Ultraviolet radiation (260nm): is quite lethal
in destroying microbes but it does not
penetrate glass, dirt films, or water
• Ionizing radiation (IR): An excellent
sterilizing agent because of its ability to
penetrate deep into objects
• IR will destroy bacterial endospores and both
prokaryotic and eukaryotic vegetative cells
UV Radiation—Serratia marcescens
Microwave Sterilization
Filtration Sterilization
Filtration
• Can be used to sterilize substances that are
destroyed by heat (drugs, serum, vitamins,
sucrose)
• To separate viruses from bacteria
(manufacture of vaccines)
• To collect microorganisms from air and
water samples (water quality testing)
Staphylococcus epidermidis on surface of
0.22mm Millipore Membrane Filter