Microbial Control

• Sterilization


  The killing or removal of all microorganisms (including viruses), absolutely essential
• Decontamination


  The treatment of an object or surface to make it safe to handle. As a result, it needs wiping off to remove fragments before using
• Disinfection


  A process that directly targets pathogens although it may not eliminate all microorganisms. It requires agents called disinfectants that actually kill microorganisms or severely inhibit their growth
• Methods in Microbial Control

  • Physical Method
  • Chemical Method
• Physical Method


  • Used extensively in industry, medicine, and the home
• Chemical Method


  • Routinely used to control microbial growth, it may be a solid, liquid, or gas
• Classes of Physical Control

  • Heat
  • Radiation
  • Filtration
• Heat


  The most widely used method of physically treating an object or substance to render it sterile
• Factors of Heat


  • Temperature
  • Time
• Higher temperatures and shorter time required to kill pathogens
• Decimal Reduction Time


  The time required for a 10-fold reduction in the viability of a microbial population at a given temperature
• Heat killing proceeds more rapidly as the temperature rises
• The relationship between time (D) and temperature is exponential, as the logarithm of D plotted against temperature yields a straight line
• Thermal Death Time


  The time it takes to kill all cells at a given temperature
• The longer time is required to kill all cells in a large population than in a small one
• Moist Heat


  Has more penetrating power and inhibits growth or kills cells more quickly than does dry heat
• Autoclave


  Sealed heating device that uses steam under pressure to kill microorganisms
• The high temperatures that are achieved when steam is placed under pressure, not the pressure inside the autoclave, that kills the microorganisms
• Pasteurization


  Uses heat to significantly reduce rather than totally eliminate the microorganisms found in liquids, such as milk
• Flash Pasteurization


  71°C for 15 seconds (or even higher temperatures for shorter time periods)
• Ultrahigh-temperature (UHT) pasteurization


  Requires heat treatment at 135°C for 1–2 sec and actually sterilizes the milk such that it can be stored at room temperature for long periods without spoilage
• Dry Heat


  Effective sterilization of metals, glassware, some powders, oils, and waxes
• Incineration (burning)


  Effective means of destroying contaminated disposable materials. Intense heat ignites and reduces microbes to ashes and gas. Limited to metals and heat-resistant glass materials
• Flaming


  Accomplished by holding the end of the loop or forceps in the yellow portion of the gas flame. Flaming the surface metal forcep and wire bacteriologic loops is an effective way to kill microorganisms
• UV Radiation


  Useful for disinfecting surfaces and air. Widely used to decontaminate and disinfect the work surface of laboratory laminar flow hoods equipped with a "germicidal" UV light, air circulating in hospital and food preparation rooms. Has very poor penetrating power, limiting its use to the disinfection of exposed surfaces or air rather than bulk objects
• Ionizing radiation


  Electromagnetic radiation of sufficient energy to produce dry heations and other reactive molecular species from molecules with which the radiation particles collide
• Filtration


  Used to separate cells, larger viruses, bacteria, certain microbes from liquids or gases in which they are suspended
• Depth filter


  Important in biosafety applications such as in a biological safety cabinet. e.g. HEPA filter (does not ensure sterilization)
• Membrane filter


  Most common filters used for liquid sterilization
• Nucleopore filter


  Commonly used to isolate specimens for scanning electron microscopy
• Antimicrobial agent


  A natural or synthetic chemical that kills or inhibits the growth of microorganisms
• • cidal agents


  Agents that actually kill microbes. The prefix indicating the type of microorganism killed. (bactericidal, fungicidal, viricidal)
• • static agents


  Agents that do not kill but only inhibit growth (bacteriotatic, fungistatic, viristatic)
• Sterilants


  e.g. ethylene oxide or aldehydes such as formaldehyde or glutaraldehyde
• Disinfectants


  e.g. phenol and cationic detergents
• Sanitizers


  Less harsh than disinfectants and reduce microbial numbers but do not sterilize
• Antiseptics or germicides


  Chemicals that kill or inhibit the growth of microorganisms but are sufficiently non toxic to animals to be applied to living tissues. Most germicides are used for hand washing or for treating surface wounds