Transcript Microbiology Chapter 12 Sterilization and Disinfection

Microbiology
Chapter 12
Sterilization and
Disinfection
Microbiology 130
R.L. Brashear-Kaulfers
Principles of Sterilization &
Disinfection
Disinfectants-applied to inanimate objects
 Antiseptics- applied to living tissue
 Some can be used as both
 Sterilization- killing or removal of all
microorganisms in a material or on an object
 Sterility- no living organisms on/in object
 Disinfection- reducing the # of pathogenic
organisms on object or in material, so they
pose no threat of disease
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Control of Microbial Growth
1out of 1 million probability is sterile
1)Total # of microbes present affects the length of
time needed to eliminate them
2) Fewer organisms present, shorter time needed
for sterility
Different microbial agents affect differently
Most susceptible phase is logarithmic phase
3) Microorganisms differ in their susceptibility to
antimicrobial agents
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Chemical Antimicrobial Agents
Potency or effectiveness of Chemical
Agents:
 Bactericidal- killing
 Bacteriostatic- growth inhibiting
 Ethyl and isopropyl alcohol- 70% effective
as it can penetrate more deeply
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Evaluating Effectiveness
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* Phenol coefficient- compare to phenol (carbolic
acid) =1 higher is more effective, lower is less
effective
Use with Staph typhi and Staph aureas standards
Used to research new disinfectants, but has
problems
* Filter Paper Method- uses small filter disks
And look for zone of inhibition-shows some
effectiveness but organic matter may interfere with
results
* Use-Dilution test: standard prep of bacteria ,
coated on stainless steel and dipped into dilutions
of agents, incubated and observed for no growth*
better results than phenol test
Disinfectant Selection-Several
Qualities
1) Should be fast acting in presence of organic
substances
 2) Be effective against all types of infectious
agents without destroying tissue or acting as a
poison if ingested
 3) Easily penetrate material to be disinfected,
without damaging/discoloring it
 4) Be easy to prepare, stable when exposed
to light, heat or other environ-mental factors
 5) Be inexpensive, easy to obtain and use
 6) Not have an unpleasant odor
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Mechanisms of Action of Chemical
Agents
Reactions that affect proteins: denaturation by
mild heat, acid, alkali destroys /alters protein
 Reactions that affect membranes: protein and
lipids- surfactants such as soaps and detergents
Do not kill but allow agents into membranes
 Reactions that affect cell components: nucleic
acids and energy production- lactic acid inhibit
fermentation and energy production in bacteria
and molds
 Reactions that affect viruses: alkylating agents
affect DNA or RNA
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Specific Chemical Antimicrobial
Agents
Soaps and detergents: remove microbes, oily deposits
and dirt, detergent-cationic (+)(food utensils), or
anionic (-) laundry and household cleaners
 Quats have amonium disinfectants: BAK, mouthwash
 Acids and Alkali: soap is a mild alkali, acid
preservatives retard mold growth in breads,
margarine, soft drinks
 Heavy Metals: selenium, mercury, copper, silver can
inhibit bacterial growth such as silver nitrate and
mercurochrome and merthiolate -tincture w/alcohol,
selenium sulfide kills fungi and spores (dandruff
shampoo)
Copper sulfate- kills algae in pools
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Specific Chemical Antimicrobial
Agents
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Halogens: Hypochlorous acid Cl, I, Br, Cloramine
Alcohols: denature proteins, skin antiseptics
Phenols: disrupt cell membranes
Oxidizing Agents:H2O2 disenfectant
Alkylating Agents: disrupt nucleic acids and protein
structures, may cause cancer, formaldehyde,
ethylene oxide, glutaraldehyde
Dyes: acridine and methylene blue, crystal violet
Other Agents: plant oils for thyme and clove,
nitrates, sulfites, sodium nitrate ( p 338)
Physical Antimicrobial Agents- Heat
Killing
Heat- thermal death point-temperature
 DRT or D value-time needed to kill 90% of
organisms
 Dry Heat- oxidizes molecules, used for
metal objects and glassware, oils and
powders. Dry heat penetrates more slowly
171C for 1 hr, 160 C for 2 hrs or 121 C for
16 hrs
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Physical Antimicrobial Agents- Heat
Killing
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Moist Heat- widely used
Autoclave at 15 lb/in pressure for 15-20
minutes, temp at 121C to kill spores
Hospital autoclave called prevacuum autoclave,
less time to sterilize
Pasteurization - kills pathogens, but not sterile
milk = 71.6 C for 15 sec (flash method), or heat
at 92.9 C for 30 min (holding method)
UHT-ultrahigh temp 74-140-74C in 5 sec used to
make coffee creamers
Physical Antimicrobial AgentsCooling, Refrigeration
Refrigeration- foods 5C , Clostridium spores
produce lethal toxins in frig
 Freezing- -20C, preserve foods on home and
industry, slows rate of microbes so they do not
spoil food. Frozen foods should not be thawed
and refrozen
 Drying- absence of water inhibits enzymes, so it
will preserve foods, drying clothes in dryer or in
sunshine can destroy pathogens
 Freeze-drying- lyophilization is drying from a
frozen state to make instant coffee, to preserve
cultures of microbes
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Physical Antimicrobial AgentsRadiation
UV-ultraviolet light-40-390nm 200nm is most
effective wavelength for killing by DNA dimers,
UV light for sewage treatment in some areas
 Ionizing radiation- X rays and gamma rays, .140nm very short
 Microwave radiation-long wavelengths 1mm-1m
 Strong visible light- sunlight, 400-700nm due to
UV
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Physical Antimicrobial Agentsother Methods
Sonic and Ultrasonic waves Filtration- passage of material through a filter,
use millipore -membrane filters 25um
Microbes on filter can be transferred to agar
(p346)
HEPA filters- clean air and capture microbes
 Osmotic Pressure- plasmolysis or loss of water
occurs with high concentration of salt, sugar
used in jellies, syrup, pickles (p 347)
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