control of microorganisms

• What is the D-Value in microbiology?

  Time for 90% reduction in viable cells
• What does the Z-Value represent?

  Temperature increase to reduce D-value by 90%
• What is the sterility assurance level (SAL) standard?

  • SAL standard is 1 x 10^-6
  • Preferably less than this value
• What factors affect sterilization?

  Resistance, physiological state, environmental factors
• If a microorganism has a D₁₂₁ of 0.25 minutes, how long to achieve SAL from 10² contamination?

  2.5 minutes
• What are the methods of control for microorganisms?

  • Physical: Heat, Irradiation, Filtration
  • Chemical: Disinfectants, Antiseptics
  • Biological methods
• What does the effectiveness of control depend on?

  Number of microbes, nature of microbes, environment
• How does microbial death occur upon exposure to a lethal agent?

  Exponential reduction at constant intervals
• Why are young, replicating cells more vulnerable?

  They are more susceptible to lethal agents
• What are the advantages of using heat for sterilization?

  • Fast and easy to use
  • Inexpensive and reliable
  • No toxic substances introduced
• What are the types of heat methods for control?

  • Dry heat
  • Moist heat
  • Pasteurization
• How does dry heat kill microorganisms?

  By oxidation of cell components
• What is microbiological contamination?

  Accidental introduction of infectious material
• What is the purpose of a Bunsen burner in the lab?

  To sterilize inoculation loops
• What is the temperature range for a hot-air oven?

  50 to 300 °C
• What are the advantages of a hot-air oven?

  • Easy to operate
  • Inexpensive
  • Minimal space required
• What are the disadvantages of a hot-air oven?

  • Cannot kill heat-resistant endospores
  • Slow and uneven heat penetration
  • Not suitable for heat-sensitive materials
• What is the purpose of incineration in sterilization?

  To destroy clinical waste
• How does moist heat kill microorganisms?

  By denaturing proteins and degrading nucleic acids
• What is the function of an autoclave?

  To sterilize using steam under pressure
• What is the typical autoclave cycle time?

  Usually around 2 hours
• What are the applications of an autoclave?

  • Rapid killing of pathogens
  • Sterilizing culture media and pipette tips
  • Used for metal instruments
• What is pasteurization used for?

  To prevent spoilage of wine
• What is the temperature for flash pasteurization?

  71.7 °C for 15 seconds
• How does ionizing radiation kill microorganisms?

  By generating free radicals that damage DNA
• What are the applications of ionizing radiation?

  • Cold sterilization of lab items
  • Preventing spoilage of food
• What is the purpose of filtration in microbial control?

  • Removal of microbes from liquids and air
  • Used for heat-sensitive solutions
• Who developed the method to prevent spoilage of wine?

  Pasteur
• What temperature range is used in pasteurization to prevent spoilage of wine?

  50-60°C
• How long should wine be held at 62.8°C during pasteurization?

  30 minutes
• What is the purpose of flash pasteurization at 71.7°C?

  Kills pathogens and spoilage organisms
• Does pasteurization sterilize the wine?

  No
• What does ionizing radiation do to kill microbes?

  Generates free radicals that break DNA bonds
• What type of radiation penetrates deep into objects?

  Gamma rays
• What is an industrial application of ionizing radiation?

  Cold sterilization of disposable lab items
• What is the purpose of filtration in microbial control?

  Removes microbes by passing liquid or gas through a filter
• What does a filter do in the filtration process?

  Acts as a barrier to retain microbes
• What type of liquids can be sterilized using filtration?

  Heat-sensitive liquids like vaccines
• What is the pore size that removes most bacteria from liquids?

  0.22 µm
• What does HEPA stand for in air filtration?

  High-Efficiency Particulate Air