Chapter 10 Sterilization, Disinfection, and Antisepsis 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

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)