CONTROL OF MICROORGANISMS BY PHYSICAL METHODS

 1.) TEMPERATURE:
              A.) HIGH TEMPERATURE: b) DRY HEAT:  Dry heat dehydrates the cell, reduces water molecules & bounds intracellular components. Dry heat is not as effective as compared to moist heat. The lab apparatus or methods designed to use dry heat for sterilization are;

  • Hot Air Oven: It is used to sterilize glassware like pipettes, flasks, dry powder etc. It is operated at a temperature 160 c for 1 hours. The above figure shows a typical hot air oven. 
  • Flaming: Here Bunsen burner is used for few seconds to sterilize bacteriological loop before removing a sample from culture tubes & after preparing a smear. Flaming is also used to sterilize tips of tube & flasks, needles, forceps, & scalpels. 
  • Incineration: It is used for destruction of corpses, infected lab animal & other infected  materials like hospital gowns, plastic apparatus. It is simply burning carried out either in incinerator or metal drums. 




B.) LOW TEMPERATURE:  Microorganisms(mos) also can be controlled by low temperature because in temperature below optimal temperature the metabolism of mos is depressed. Since microbial growth is restricted at low temperature, this temperature can be used preservation of food. Eg; Use of Refrigeration: Agar slants of bacteria can be stored at 4-7 c. Many bacteria & virus can be maintained in deep freeze at -20 to -70 c. Liquid Nitrogen at a temperature -169 c is used for preservation of culture of many bacterial & viruses, mammalian tissue cells etc.  

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