chapter 26 (1) Flashcards
Physical Antimicrobial Control
Sterilization: killing or removal of all viable organisms.
Inhibition: effectively limiting microbial growth.
Decontamination: tx of an object to make it safe.
Disinfection: directly targets pathogens.
Heat sterilization
Most widely used method of controlling microbial growth.
-high temps denature macromolecules.
-decimal reduction time: time required to reduce viability tenfold.
Endospores:
-can survive heat that would rapidly kill vegetative cells.
The autoclave
Sealed device that uses steam under pressure
- allows temperature of water >100*C.
- Not pressure that kills, but temp.
Pasteurization
Process of using precisely controlled heat to reduce microbial load in heat sensitive liquids.
- does not kill organisms, different than sterilization.
- retards growth of spoilage organisms, increasing shelf life.
- Milk through heat exchanger at 71 for 15 seconds then rapidly cooled.
Radiation Sterilization
Microwaves, UV, x-rays, gama rays and electrons can reduce microbial growth.
UV can damage DNA
-useful for decontamination of surfaces.
-cannot penetrate solid, opaque or light absorbing surfaces.
–radiation used for sterilization in medicine and food industry.
Ionizing radiation
- electromagnetic radiation that produce ions and other reactive molecules.
- generates electrons, hydroxyl radicals, etc…
- some microorganisms more resistant to radiation.
Filter sterilization
Filtration avoids use of heat on sensitive liquids and gases.
–Pores of filter too small for organisms to pass through.
Chemical growth control
Antimicrobial agents can be classified as bacteriostatic, bactericidal and bacteriolytic.
Minimum inhibitory concentration
(MIC): smallest amount of agent needed to inhibit growth.
-varies with organism, inoculum size, temp, pH…
Disc diffusion assay
Antimicrobial agent added to filter paper disc.
MIC reached at some distance.
–Zone of inhibition: area of no growth.
