BIOL 3702: Chapter 8
Spring 2015
Definitions
u  Sterilization - destruction or removal of all
BIOL 3702: Chapter 8
viable organisms from an object or environment
(agent = sterilant)
u  Disinfection - killing, inhibition, or removal of
pathogenic microorganisms (mainly pertains to
inanimate objects) (agent = disinfectant)
u  Sanitization - reducing microbial populations to
a safe level in accord with public health
standards (agent = sanitizer)
Control of Microbes
in the Environment
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 1
Definitions (cont.)
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 2
Definitions (cont.)
u  Antisepsis -
u  -cide - a suffix indicating that the agent will
prevention of
microbial infection
on living tissue
(agent = antiseptic)
u  Chemotherapy prevention of
microbial infection
within living tissue
kill the kind of organism in question (e.g.,
viricide)
u  -static - a suffix indicating that the agent will
prevent the growth of the type of organism in
question (e.g., bacteriostatic)
Figure 8.2
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 3
u  Microorganisms are not killed instantly when
exposed to a lethal agent
u  Population death decreases by a constant
fraction at constant intervals (exponential
killing)
u  A microorganism is considered dead when it
is unable to grow in conditions that would
normally support its growth
Dr. Cooper
Slide No. 4
Mechanical Removal Methods
Pattern of Microbial Death
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 5
u  Filtration - sterilizes heat-sensitive liquids
and gases by removing microorganisms
rather than destroying them
v  Depth filters - thick fibrous or granular filters that
remove microbes by physical screening,
entrapment, or adsorption
v  Membrane filters - thin filters with defined pore
sizes that remove microorganisms
v  High-efficiency particulate air (HEPA) filters used in biological safety cabinets to sterilize air
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 6
1
BIOL 3702: Chapter 8
Spring 2015
Filter unit and filtration apparatus
Figure 8.4a
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 7
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Figure 8.5
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 9
Slide No. 8
Figure 8.6
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 10
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 12
Physical Methods of Control
u  Heat
v  Moist heat
Ø  Boiling water is effective against vegetative cells and
eukaryotic spores, but not bacterial spores
Ø  Autoclaving (steam under pressure) is effective
against vegetative cells and most bacterial
endospores
Ø  Quality control - includes strips with Geobacillus
stearothermophilus
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Dr. Cooper
Slide No. 11
2
BIOL 3702: Chapter 8
Spring 2015
Physical Methods of Control (cont.)
The
Autoclave
Figure 8.7
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 13
v  Pasteurization
Ø  A process involving brief exposure to temperatures
below the boiling point of water
Ø  Reduces the total microbial population
Ø  NOT STERILIZATION
Ø  Often used for heat-sensitive materials
v  Tyndallization
Ø  A process involving multiple brief exposures to
temperatures below the boiling point of water
Ø  Used for materials that cannot withstand the high
temperatures of autoclaving
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 14
Physical Methods of Control (cont.)
v  Dry heat can be used to sterilize moisture-
sensitive materials such as powders, oils, and
similar items
Ø  Less efficient than moist heat
Ø  Usually requires higher temperatures (160 to 170°C)
and longer exposure times (2 to 3 hrs)
v  Incineration – often used to sterilize re-usable
items, e.g., microbiological loops
Figure 8.8
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 15
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 16
Physical Methods of Control (cont.)
u  Radiation
v  Ultraviolet (UV) radiation is effective, but its use
is limited to surface sterilization because UV
radiation does not penetrate glass, dirt films,
water, and other substances
v  Ionizing radiation (X rays, gamma rays, etc.) is
effective and penetrates the material
Figure 8.10
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Dr. Cooper
Slide No. 17
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 18
3
BIOL 3702: Chapter 8
Spring 2015
Chemical Agents in Control
u  Disinfectant must be effective against wide
variety of infectious agents at low
concentrations
v  Must be effective in the presence of organic
matter; should be stable in storage
v  Overuse of antiseptics such as triclosan has
selected for triclosan resistant bacteria and
possibly antibiotic resistant
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 19
Chemical Agents in Control (cont.)
u  Halogens
v  Widely used antiseptics and disinfectant
v  Examples
Ø  Iodine: oxidizes cell constituents and iodinates cell
proteins
Ø  Chlorine: oxidizes cell constituents
u  Heavy metals
v  Effective but usually toxic
v  Act by combining with proteins and inactivating
them
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 21
Chemical Agents in Control (cont.)
u  Quaternary ammonium compounds
v  Cationic detergents of low toxicity
v  Uses:
Ø  Disinfectants for food utensils and small instruments
Ø  Skin antiseptic
v  Act by disrupting biological membranes and
possibly by denaturing proteins
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Dr. Cooper
Slide No. 23
Chemical Agents in Control (cont.)
u  Phenolics
v  Laboratory and hospital disinfectants
v  Act by denaturing proteins and cell membranes
u  Alcohol
v  Widely used disinfectants and antiseptics
v  Will not kill endospores
v  Act by denaturing proteins and possibly by
dissolving membrane lipids
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 20
Chemical Agents in Control (cont.)
u  Aldehydes
v  Reactive molecules
that can be used as
chemical sterilants,
but may irritate the
skin
v  Act by combining
with proteins and
inactivating them
Figure 8.11
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 22
Chemical Agents in Control (cont.)
u  Sterilizing gases (e.g., ethylene oxide)
v  Used to sterilize heat-sensitive materials
v  Act by combining with proteins and inactivating
them
u  Vapor-phase hydrogen peroxide has been
used to decontaminate biological safety
cabinets
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 24
4
BIOL 3702: Chapter 8
Spring 2015
Conditions Affecting
Antimicrobial Activity
Conditions Affecting
Antimicrobial Activity (cont.)
u  Population size - larger populations take
longer to kill than smaller populations
u  Population composition - microorganisms
differ markedly in their sensitivity to various
agents
u  Concentration or intensity of the
antimicrobial agent - higher concentrations
or intensities are generally more efficient,
but the relationship is not linear
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 25
u  Duration of exposure - longer the exposure,
the greater the number of organisms killed
u  Temperature - higher temperatures will often
(but not always) increase the effectiveness
of killing
u  Local environment - environmental factors,
such as pH, viscosity, and concentration of
organic matter, can profoundly influence the
effectiveness of a antimicrobial agent
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Slide No. 26
Biological Control of Microbes
u  Emerging field showing
great promise
u  Natural control
mechanisms
v  Predation by Bdellovibrio
v  Viral-mediated lysis using
pathogen specific
bacteriophage lysins
v  Toxin-mediated killing using
bacteriocins
Annual Review of Microbiology 63: 523-539, 2009
BIOL 3702: Microbiology (2015)
Portions Copyright © The McGraw-Hill Companies, Inc. and Copyright © C. R. Cooper, Jr.
Dr. Cooper
Slide No. 27
5