FACTORS THAT INFLUENCE THE EFFECTIVENESS 1. Number of microbes—the more there are to begin with, the longer it takes to eliminate them all. 2. Microbial characteristics—susceptibility to different agents varies among microbes. Also, endospores are much more difficult to eliminate. 3. Environmental factors: a. Organic matter (blood, feces, etc.) often interferes with chemical antimicrobials, and also to a lesser extent with heat treatment. Any medium containing fats or proteins tends to protect bacteria. b. pH—heat is more effective in an acid pH. 4. Time of exposure a. The lower the temperature used for heat treatment, the longer the time required. b. Effects of irradiation are also related to time. c. Chemical antimicrobials require extended exposure to kill resistant bacteria or endospores.
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