BIO 300N

• Sterilization


  Killing or removing all forms of microbial life (including endospores) in a material or an object
• Heating


  • The most commonly used method of sterilization
• Commercial sterilization


  Heat treatment that kills endospores of Clostridium botulinum the causative agent of botulism, in canned food
• Commercial sterilization does not kill endospores of thermophiles, which are not pathogens and may grow at temperatures above 45oC

  
• Disinfection


  Reducing the number of pathogenic microorganisms to the point where they no longer cause diseases
• Methods of disinfection


  • Physical
  • Chemical
• Disinfectant


  Applied to inanimate objects
• Antiseptic


  Applied to living tissue
• Antisepsis


  Antiseptic applied to living tissue
• Degerming


  Mechanical removal of most microbes in a limited area
• Degerming


  • Alcohol swab on skin
• Sanitization


  Use of chemical agent on food-handling equipment to meet public health standards and minimize chances of disease transmission
• Sanitization


  • Hot water and soap
• Sepsis


  Bacterial contamination

  
• Asepsis


  Absence of significant contamination
• Aseptic techniques


  Used to prevent contamination of surgical instruments, medical personnel, and the patient during surgery, and to prevent bacterial contamination in food industry

  
• Bacteriostatic agent


  An agent that inhibits the growth of bacteria, but does not necessarily kill them
• Germicide


  An agent that kills certain microorganisms
• Types of germicides


  • Bactericide
  • Viricide
  • Fungicide
  • Sporicide
• Bactericide


  An agent that kills bacteria. Most do not kill endospores
• Viricide


  An agent that inactivates viruses
• Fungicide


  An agent that kills fungi
• Sporicide


  An agent that kills bacterial endospores or fungal spores
• When bacterial populations are heated or treated with antimicrobial chemicals, they usually die at a constant rate
• Factors affecting the efficacy of antimicrobial methods

  • Site to be treated
  • Number of microbes
  • Type of microbes
  • Environmental influences
  • Temperature and time of exposure

  
• Site to be treated

  Will determine the choice of antimicrobials that can be used

  
• Number of microbes


  The more microbes present, the more time it takes to eliminate the population
• Type of microbes


  Endospores are very difficult to destroy. Vegetative pathogens vary widely in susceptibility to different methods of microbial control

  
• Environmental influences


  Presence of organic material (blood, feces, saliva) tends to inhibit antimicrobials, pH etc.
• Temperature and time of exposure

  Chemical antimicrobials and radiation treatments are more effective at longer times. In heat treatments, longer exposure compensates for lower temperatures
• Thermal death point (TDP)

  Lowest temperature at which all of the microbes in a liquid suspension will be killed in ten minutes
• Thermal death time (TDT)


  Minimal length of time in which all bacteria will be killed at a given temperature
• Decimal reduction time (DRT)


  Time in minutes at which 90% of bacteria at a given temperature will be killed. Used in canning industry

  
• Moist heat


  Kills microorganisms by coagulating their proteins. Much more effective than dry heat
• Boiling


  Heat to 100oC or more at sea level. Kills vegetative forms of bacterial pathogens, almost all viruses, and fungi and their spores within 10 minutes or less. Endospores and some viruses are not destroyed this quickly
• Hepatitis virus can survive up to 30 minutes of boiling
• Endospores can survive up to 20 hours or more of boiling
• Autoclave


  Chamber which is filled with hot steam under pressure. Preferred method of sterilization, unless material is damaged by heat, moisture, or high pressure. Temperature of steam reaches 121oC at twice atmospheric pressure. Most effective when organisms contact steam directly or are contained in a small volume of liquid. All organisms and endospores are killed within 15 minutes
• Pasteurization


  Developed by Louis Pasteur to prevent the spoilage of beverages by reducing the number of microbes in milk, wine, juices, beer, etc.
• Methods of pasteurization


  • Classic method (65oC for 30 minutes)
  • Flash (high temperature short time) pasteurization (72oC for 15 seconds)
  • Ultrahigh temperature pasteurization (134oC for 1 second)
  • Ultrahigh temperature sterilization (140oC for 1-3 seconds and then cooled very quickly in a vacuum chamber)