9. Microbial Control and Destruction

• Microbial control


  Essential to prevent unwanted microbial contamination, transmission of disease and infection, stop decomposition and spoilage of food
• Microbial control


  Achieved by limiting or inhibiting growth, using physical agents and chemical agents
• Sterilization


  • Removal or destruction of all living microorganisms, including viruses
• Decontamination


  Treatment of an object or surface to make it safe to handle, requires wiping off fragments before using
• Disinfection


  Process that directly targets pathogens, may not eliminate all microorganisms, uses disinfectants that kill microorganisms or severely inhibit their growth
• Sepsis


  Presence of pathogens in blood or tissue
• Asepsis


  Absence of pathogens
• Antisepsis


  Prevention of infection
• Microbial control


  Killing or inhibiting the growth of microorganisms
• Heating


  • Most common method for killing microbes, including the most resistant forms like endospores
• Filtration


  Separates cells, larger viruses, bacteria, certain microbes from liquids and gases in which they are suspended, removes contaminants instead of killing them
• Physical methods of microbial control


  • Heat
  • Radiation
  • Filtration
• Heat sterilization


  • Effectiveness determined by time and temperature, higher temp and shorter time required to kill pathogens
• Decimal reduction time


  Time required for a 10-fold reduction in the viability of a microbial population at a given temperature
• Heating killing


  Proceeds more rapidly as temperature rises
• Thermal death time


  Time it takes to kill all cells at a given temperature, affected by population size
• Moist heat


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


  Sealed heating device that uses steam under pressure to kill organisms, not the pressure but the high temperature that kills microorganisms
• Autoclave tape


  • Marks appear after autoclaving
• Biological indicators


  Used to monitor the effectiveness of steam sterilization
• Pasteurization


  Uses heat to significantly reduce rather than totally eliminate microorganisms in liquids like milk
• Dry heat


  • Effective for sterilizing metals, glassware, some powders, oils and waxes
• Dry heat methods


  • Incineration
  • Flaming
• Ultraviolet radiation


  • Useful for disinfecting surfaces and air, poor penetrating power limits use to exposed surfaces or air
• Ionizing radiation


  Electromagnetic radiation of sufficient energy to produce ions and other reactive molecular species
• Filtration


  Unique method of sterilization as it removes contaminants instead of killing them
• Antimicrobial agent


  Natural or synthetic chemical that kills or inhibits the growth of microorganisms
• Cidal agents


  Kill microbes
• Static agents


  Inhibit the growth of microbes
• Bacteriolytic agent


  Causes lysis of bacterial cells
• Classes of chemical antimicrobial agents


  • Sterilants
  • Disinfectants
  • Antiseptics or germicides
• Sanitizers


  Less harsh than disinfectants, reduce microbial numbers but do not sterilize