MBIO 1010- L18

• Sterilization

  • the killing or removal of all viable organisms within a growth medium
• Inhibition

  • effectively limiting microbial growth
  • no killing taking place
• decontamination

  • the treatment of an object to make it safe to handle
• disinfection

  • directly targets the removal of all pathogens
  • not necessarily all microorganisms
• Physical forms of microbial control

  • heat
  • radiation
  • filtration
• heat sterilization

  • the most widely used method of controlling microbial growth
  • high temperatures denature macromolecules
• amount of time required to reduce viability tenfold is called the decimal reduction time (D)

  time it takes for a 10 fold reduction in bacterial numbers
• some bacteria produce resistant cells called endospores, they can survive heat that would rapidly kill vegetative cells
• D is dependent on temperature

  • at lower temperatures you would need a longer time to kill, increasing the decimal time
• Moist heat would be humidity and it is able to better penetrate and kill more quickly than a dry heat
• Pasteurization

  • the process of using precisely controlled heat to reduce the microbial load in heat-sensitive liquids (not boiling)
  • does not kill all organisms -> not sterilization
• In the case of milk, many different time and temperature combinations can be used

  • LTLT (Low-temperature, long time)
  • 63 degrees for 30 minutes
  • HTST (High-temperature, short time)
  • 72 degrees for 15 seconds
  • both processes kill Coxiella burnetii, the causative agent of Q fever, which is the most heat resistant pathogen found in milk
• The Autoclave

  • a sealed device that uses steam under pressure
  • allows temperature of water to get above 100 degrees
  • 121 degrees for 15 minutes at 15 psi is typically used
  • to ensure sterility this means that the point that takes the longest to heat must stay at 121 degrees for 15 minutes
• radiation

  • microwaves aren't really helping with microbial control, it is just because they are heating things
  • UV, X-rays, gamma rays and electrons can reduce microbial growth
  • UV has sufficient energy to cause modifications and breaks in DNA
  • UV is useful for decontaminating surfaces
  • cannot penetrate solid, opaque, or light-absorbing surfaces
• Ionizing radiation

  • electromagnetic radiation that produces ions and other reactive molecules generates electrons, hydroxyl radicals and hydride radicals
  • some microorganisms are more resistant to radiation than others
  • amount of energy required to reduce viability tenfold is analogous to D value
• endospores are resistant to radiation
• sources of radiation include cathode ray tubes, X-rays and radioactive nuclides
• radiation is used for sterilization in the medical field and food industry

  • radiation is approved by the WHO and is used in the USA for decontaminating foods particularly susceptible to microbial contamination
  • hamburger, chicken, spices may all be irradiated