1. Chapter 10 Sterilization, Disinfection, and Antisepsis
Medical Microbiology
Chapter 10
Sterilization, Disinfection, and Antisepsis

2. Control of Microbial Growth
Historical perspective of the control of microbial growth
Civil War, etc.

3. 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

4. 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

5. 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

6. 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

7. Physical Methods
Moist heat - steam under pressure is the most efficient sterilizing agent
Autoclaving
Boiling water - kills all vegetative cells within a few minutes

8. 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

9. Physical Methods (cont.)
Dry heat - takes longer and/or higher temperatures than moist heat to kill microbes
Why?
Flaming
Dry heat oven °C for 1-2 hours
used for materials that would be damaged by steam
powders, special wraps and dressings, some glassware

10. 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)

11. 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.

12. 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)