CONTROL AND DESTRUCTION OF MICROORGANISMS (Module 10)

• Sterilization


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


  Heat treatment that kills endospores of Clostridium botulinum the causative agent of botulism, in canned food. 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. Usually involves the removal of vegetative or non-endospore forming pathogens. May use physical or chemical methods
• Disinfectant


  Applied to inanimate objects
• Antiseptic


  Applied to living tissue (antisepsis)
• Degerming


  Mechanical removal of most microbes in a limited area. Example: Alcohol swab on skin
• Sanitization


  Use of chemical agent on food-handling equipment to meet public health standards and minimize chances of disease transmission. E.g: Hot soap & water
• Sepsis


  Comes from Greek for decay or putrid. Indicates bacterial contamination
• Asepsis


  Absence of significant contamination
• Aseptic techniques


  Used to prevent contamination of surgical instruments, medical personnel, and the patient during surgery. Aseptic techniques are also used to prevent bacterial contamination in food industry
• Bacteriostatic Agent


  An agent that inhibits the growth of bacteria, but does not necessarily kill them. Suffix stasis: To stop or steady
• Germicide


  An agent that kills certain microorganisms
• Bactericide


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


  An agent that inactivates viruses
• Fungicide


  An agent that kills fungi
• Sporocide

  An agent that kills bacterial endospores of fungal spores
• When bacterial populations are heated or treated with antimicrobial chemicals, they usually die at a constant rate
• The rate of microbial death can be determined
• It is important to develop standard protocols for disinfection which will facilitate the sterilization routine in many industries
• The goal is to find out what is the minimum time needed to achieve acceptable level of sterilization for a specific purpose
• The killing agent can be different (e.g., heat, chemical with certain concentration) depending on the specific application
• Factors that influence the effectiveness of antimicrobial treatment


  • Number of Microbes
  • Type of Microbes
  • Environmental influences
  • Time of Exposure
• Number of Microbes


  The more microbes present, the more time it takes to eliminate 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
• Time of Exposure

  Chemical antimicrobials and radiation treatments are more effective at longer times. In heat treatments, longer exposure compensates for lower temperatures
• Moist Heat


  Kills microorganisms by coagulating their proteins. In general, moist heat is much more effective than dry heat
• 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
• Boiling heat to 100°C or more at sea level kills vegetative forms of bacterial pathogens, almost all viruses, and fungi and their spores within 10 minutes or less
• Hepatitis virus can survive up to 30 minutes of boiling
• Endospores can survive up to 20 hours or more of boiling
• Tyndallization


  The steaming process performed at 100°C is done in steam sterilizer for 20 minutes followed by incubation at 37°C overnight and this cycle is repeated for successive 2 days
• 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 121°C 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. Used to reduce microbes responsible for spoilage of beer, milk, wine, juices, etc.
• Classic Method of Pasteurization

  Milk was exposed to 65oC for 30 minutes

  
• High Temperature Short Time Pasteurization (HTST)


  Milk is exposed to 72oC for 15 seconds
• Ultra High Temperature Pasteurization (UHT)


  Milk is treated at 140oC for 3 seconds and then cooled very quickly in a vacuum chamber. Advantage: Milk can be stored at room temperature for several months
• Vaccine bath


  Contaminating bacteria in a vaccine preparation can be inactivated by heating in a water bath at 60°C for one hour