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The Control of Microbial Growth

7. The Control of Microbial Growth. The Control of Microbial Growth. Sepsis refers to microbial contamination. Antisepsis : chemical method for disinfection directed at living tissue The chemical is called an antiseptic Asepsis is the absence of significant contamination.

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The Control of Microbial Growth

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  1. 7 The Control of Microbial Growth

  2. The Control of Microbial Growth • Sepsisrefers to microbial contamination. • Antisepsis: chemical method for disinfection directed at living tissue • The chemical is called an antiseptic • Asepsisis the absence of significant contamination. • Asepticmeans that an object or area is free of pathogens • Aseptic surgery techniques prevent microbial contamination of wounds.

  3. Terminology • Sterilization: Removal of all microbial life • Commercial sterilization: Killing C. botulinum endospores • Disinfection: Removal of pathogens • Antisepsis: Removal of pathogens from living tissue • Degerming: Removal of microbes from a limited area • Sanitization: Lower microbial counts on eating utensils • Biocide/Germicide: Kills microbes • Bacteriostasis: Inhibiting, not killing, microbes

  4. Effectiveness of Antimicrobial Treatment • Depends on: • Number of microbes • Environment (organic matter, temperature, biofilms) • Time of exposure • Microbial characteristics Figure 7.1b

  5. Actions of Microbial Control Agents • Alternation of membrane permeability • Damage to proteins • Damage to nucleic acids

  6. Moist Heat vs. Dry Heat • Heat appears to kill microorganisms by denaturing their enzymes; inactivates them • Moist heat: kills microorganisms primarily by the coagulation of proteins (breaking hydrogen bonds to change their structure) • Boiling, autoclave • Dry heat: kills by oxidation effects • Flaming: sterilizing inoculating loops

  7. Physical Methods of Microbial Control • Filtration removes microbes • Low temperature inhibits microbial growth • Refrigeration • Deep freezing • Lyophilization • High pressure denatures proteins • Desiccation prevents metabolism • Osmotic pressure causes plasmolysis

  8. Physical Methods of Microbial Control • Pasteurization reduces spoilage organisms and pathogens • Equivalent treatments • 63°C for 30 min • High temperature, short time: 72°C for 15 sec • Ultra high temperature: 140°C for <1 sec • Thermoduric organisms survive

  9. Chemical Methods of Microbial Control • Principles of effective disinfection • Concentration of disinfectant • Organic matter • pH • Time

  10. Chemical Methods of Microbial Control • Evaluating a disinfectant • Disk-diffusion method Figure 7.6

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