Chapter 23 Outline

Chapter 23 Outline - Chapter 23 Physical and Chemical...

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Chapter 23 Physical and Chemical Control of Microorganisms Introduction 23.1 General Principles of Microbial Control Sterilization and Sanitation Are Key to Good Public Health Sterilization involves destruction of all living microbes, spores, and viruses Sterile objects become contaminated when exposed to air and surroundings Sanitization reduces the numbers of pathogens or discourages their growth 23.2 Physical Methods of Control Heat Is One of the Most Common Physical Control Methods At heats above the growth range, proteins and nucleic acids are destroyed and water is removed Each microbial species has a thermal death time for a given temperature Each species has a thermal death point, the minimum temperature at which it dies in a given time period Incineration uses direct flame to kill microbes Dry and Moist Heat Are Applied Differently Dry heat requires long periods of exposure to high temperatures The heat changes microbial proteins and removes water, slowly burning the microbes Moist heat (like boiling water) is faster and effective at a lower temperature than dry heat Moist heat kills microbes by denaturing their proteins Boiling water may not kill all spores or inactivate all viruses Pressurized steam is used in an autoclave to sterilize a variety of objects and media The prevacuum autoclave decreases cycle time and exposure of sensitive materials to
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Chapter 23 Outline - Chapter 23 Physical and Chemical...

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