microbio Textbook notes .docx

microbio Textbook notes .docx - Chapter 9 Principles of...

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Chapter 9 Principles of Microbial control: Sterilization – eradication of microorganisms and viruses; not applied to the destruction of prions Aseptic – free of contamination by pathogens Antisepsis – inhibition/killing of microorganisms on skin or tissue by the use of chemical antiseptic. Disinfection – use of agents (disinfectants) to inhibit microbes on inanimate objects De-germing – removal of microbes from a surface by scrubbing Sanitization – reduction of a prescribed number of pathogens from surfaces or utensils in public settings Pasteurization – using heat to kill pathogens and control microbes that cause spoilage of food and beverages Suffix –stasis and static – inhibits microbes Suffix –cide and –cidal – kills or permanently inactivates type of microbe Microbial death – loss of reproductive capacity Microbial death rate – efficacy of an antimicrobial agent Antimicrobial agents – destroy microbes Selection of Microbial Control Methods: Factors affecting efficacy – site to be treated, susceptibility of microorganisms and environmental conditions Biosafety levels – BSL-1: minimal; BSL-4: requires special suites, rooms and other precautions. Physical methods of Microbial Control: Thermal death point – lowest temperature that kills all cells in broth Thermal death time – time it takes to completely sterilize particular volume of liquid Decimal reduction time – time required to destroy 90% of the microbes in the sample Autoclave – uses steam heat under pressure to sterilize chemicals and objects Pasteurization – Three methods: batch method, flash method and ultra-high-temperature method Microbes can be controlled using – ultra-high-temperature sterilization, dry-heat sterilization, incineration, refrigeration and freezing Antimicrobial methods – desiccation (Drying to preserve food), lyophilisation (freeze drying for long term storage) Osmotic pressure – hypertonic solutions of salt or sugar can preserve foods such as jerky and jams, removing the water Ionizing radiation – wavelength shorter than 1nm, produces ions that denature important molecules and kill cells (gamma, x-rays, electron) Non-ionizing Radiation – wavelength longer than 1nm, less effective in microbial control but UV light can kill affected cells (UV) Chemical methods of microbial control: Phenolic – modified phenol molecules. Denature proteins and disrupt cell membranes. Intermediate to low level Alcohols – intermediate level. Denature proteins and disrupt cell membranes. 70-90% aqueous solution Halogens – kill microbes by protein denaturation in water or on medical instruments or skin Oxidizing agents – hydrogen peroxide and ozone. Release oxygen radicals which are toxic to many microbes Surfactant – (soaps and detergents) break up oils during de-germing Heavy metal ions – have been superseded by less toxic alternatives Aldehydes – high level disinfectants. Disinfect or sterilize medical or dental equipment and in embalming fluid
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