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LOW TEMPERATURES - 3 QUICK-FREEZING IN LIQUID NITROGEN AND...

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LOW TEMPERATURES These are much more often bacteriostatic that bacteriocidal. Although some species are fairly  easily damaged, low temperatures are never a dependable means of killing microbes.  1. NORMAL REFRIGERATOR TEMPERATURES  —very few pathogens can grow.  Psychrotrophs grow slowly, and with time can cause food spoilage. This is a means of  preservation of foods, drugs, microbiological cultures, etc. Remember, refrigerator temperatures  do not kill many pathogens, so food allowed to sit at room temperature for prolonged times  before refrigeration can be dangerous.  2. FREEZING IN REGULAR HOME FREEZERS —this may kill some bacteria, but at least  some will usually survive even a year of freezing. Some bacteria are even able to grow very  slowly at several degrees below freezing. 
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Unformatted text preview: 3. QUICK-FREEZING IN LIQUID NITROGEN AND FREEZE-DRYING (LYOPHILIZATION)— these are means of preserving cultures, not of killing bacteria. HIGH PRESSURE Applying high pressure to liquid suspensions can inactivate vegetative cells by altering the molecular structure of proteins and carbohydrates. Endospores are relatively resistant. DESICCATION Desiccation or drying can kill microbe. Loss of moisture causes cells to either become dormant or die because there is insufficient water for cellular reactions to proceed. Species vary in their susceptibility. Dry surroundings kill some vegetative cells in one hour or less. Others can survive for months. Bacteria that produce endospores are extremely resistant to drying. Many viruses are also resistant to drying....
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