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PHYSICAL METHODS OF CONTROL - retain microbes This method...

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PHYSICAL METHODS OF CONTROL  Drying and salting were the earliest methods of food preservation, so these were also the earliest  means of controlling bacterial growth. Physical means of control include: Heat Osmotic pressure Filtration Radiation Low temperatures Desiccation When choosing among modern physical methods, several factors must be considered: 1. Substance must not be inactivated by the treatment—certain injectables such as vitamins and  hormones are inactivated by heat, for example 2. Material must not be destroyed—rubber seals, latex tubing, etc. are damaged by heat 3. Economics—labor involved in cleaning and sterilizing may make presterilized disposables  more economic FILTRATION This is the passage of a liquid or gas through a screenlike material with pores small enough to 
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Unformatted text preview: retain microbes. This method is used to sterilize items that would be destroyed by heat. Some examples are: Certain culture media Enzymes Vaccines Injectable antibiotics HEPA (high-efficiency particulate air filters) trap microbes larger than 0 . 3 μ m in diameter. They are sometimes used in operating rooms and rooms of transplant patients to lower numbers of bacteria. To filter liquids, filters of unglazed porcelain were originally used. Bacteria were removed but viruses went through. For this reason, they were called filterable viruses. In recent years, membrane filters have been developed. These are made of cellulose or plastic and the size of the pores can be selected, down to a size that will even retain most viruses....
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