Ch7Notes - Chapter 7-The Control of Microbial Growth I...

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Chapter 7—The Control of Microbial Growth I. Terminology of Microbial Growth. Table 7.1. a. Sterilization: Removal or destruction of all microbial life. i. Commonly done by heating, but filtration can sterilize liquids and gasses, also. b. Commercial sterilization. i. Concerned with killing Clostridium botulinum endospores in canned food, which produce fatal toxins. ii. Endospores of thermophiles survive; they do not grow at the temperatures at which canned foods are stored. 1. Incubation above ~45°C would result in significant food spoilage by these organisms in canned food. c. Disinfection. i. Normally refers to the destruction of vegetative pathogens that do not form endospores. ii. Can be accomplished by using chemicals (disinfectants), UV radiation, boiling water, or steam. d. Antisepsis. i. Removal of pathogens from living tissue. ii. Chemical used is called an antiseptic. e. Degerming. i. Mechanical removal of microbes from a limited area. ii. Generally does not kill microorganisms. f. Sanitization. i. Lowers microbial counts on eating utensils to safe public health levels. g. Biocide/Germicide. i. Kills microbes, but not usually endospores. ii. Fungicides kill fungi. iii. Virucides inactivate viruses. h. Bacteriostasis. i. Inhibiting the growth of microbes without necessarily killing them. i. Sepsis refers to microbial contamination. j. Asepsis is the absence of significant contamination. k. Aseptic surgery techniques prevent microbial contamination of wounds. i. Lister, 1867, phenol (carbolic acid). II. Rate of Microbial Death. a. Bacterial populations die at a constant logarithmic rate when heated or treated with antimicrobial chemicals. Fig. 7.1, Table 7.2. b. Effectiveness of antimicrobial treatment depends on: i. Number of microbes present at the beginning of the treatment. ii. Environment (temperature, pH, presence of organic matter or biofilms, concentration of antibiotic…). iii. Time of exposure. iv. Microbial characteristics. III. Actions of Microbial Control Agents. a. Alteration of membrane permeability/cell wall integrity. i. Damage to the plasma membrane’s lipids or proteins can cause cellular contents to escape and interfere with normal metabolism. b. Damage to intracellular proteins. i. Denature proteins and enzymes by targeting hydrogen bonds or disulfide bridges. c. Damage to nucleic acids. i. Often kills the cell.
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IV. Physical Methods of Microbial Control. a. Heat. i. Kills microorganisms by denaturing proteins and enzymes.
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