UNIT 6

• What is the opposite of microbial growth discussed in the chapter?

  Microbial growth control
• How do bacterial populations typically die when treated?

  At a constant rate
• If 90% of 1 million microbes die after 1 minute, how many remain?

  100,000 microbes
• What happens to the microbial population after each minute of treatment?

  90% of the remaining population dies
• What does a logarithmic plot of the death curve indicate?

  The death rate is constant
• What factors influence the effectiveness of antimicrobial treatments?

  • Number of microbes
  • Environmental influences
  • Nature of the suspending medium
  • Time of exposure
  • Microbial characteristics
• What is sterilization?


  Destruction of all forms of microbial life
• What is commercial sterilization aimed at?


  Killing endospores of Clostridium botulinum
• What does disinfection achieve?


  Destruction of vegetative pathogens
• What is antisepsis?


  Destruction of pathogens on living tissue
• What is degerming?


  Removal of microbes from a limited area
• What is sanitization intended to do?


  Lower microbial counts to safe levels
• How does organic matter affect disinfectants?

  It inhibits the action of chemical antimicrobials
• Why are microbes in surface biofilms difficult to kill?

  Biofilms hinder biocide penetration
• How does temperature affect disinfectant activity?

  Disinfectants work better under warm conditions
• What is the effect of fats and proteins on heat treatment?

  They protect microbes, increasing survival rates
• How does time of exposure affect chemical antimicrobials?

  Longer exposure is needed for resistant microbes
• What do microbial characteristics influence?

  The choice of control methods
• What is biosafety?

  Containment principles to prevent exposure
• What does biosecurity focus on?

  Protection and accountability for biological materials
• What are the characteristics of Biosafety Level 1 (BL1)?

  • No special containment equipment required
  • Supervised by trained scientists
  • Suitable for agents of minimal hazard
• What distinguishes Biosafety Level 2 (BL2) from BL1?

  • Personnel trained to handle pathogens
  • Limited access during work
  • Use of safety cabinets for certain procedures
• What are the features of Biosafety Level 3 (BL3)?

  • Training in handling lethal agents
  • Supervised by experienced scientists
  • Work conducted in safety cabinets
• What are the requirements for Biosafety Level 4 (BL4)?

  • Highest containment conditions
  • Double-doored autoclave for material passage
  • Whole-body sealed suits for personnel
• What is the primary action of moist heat in microbial control?

  Protein denaturation
• What is the effect of boiling or flowing steam?

  Kills vegetative pathogens and most viruses
• What is autoclaving effective for?

  Sterilizing microbiological media and equipment
• What does pasteurization achieve?

  Kills all pathogens and most nonpathogens
• What is the mechanism of action for dry heat sterilization?

  Oxidation
• What is the purpose of filtration in microbial control?

  Separates bacteria from liquids or gases
• How does refrigeration affect microbial growth?

  Has a bacteriostatic effect
• What is lyophilization used for?

  Long-term preservation of microbial cultures
• What is the effect of high pressure on microbial cells?

  Alters molecular structure of proteins
• What does desiccation do to microbes?

  Disrupts metabolism
• What is the effect of osmotic pressure on microbial cells?

  Causes loss of water from cells
• What is the action of ionizing radiation?

  Destruction of DNA
• What is the effect of nonionizing radiation?

  Damages DNA
• What are the physical methods used to control microbial growth?

  • Heat (moist and dry)
  • Filtration
  • Cold (refrigeration, deep-freezing, lyophilization)
  • High pressure
  • Desiccation
  • Osmotic pressure
  • Radiation (ionizing and nonionizing)
• What is the preferred use of boiling or flowing steam?

  Dishes and various equipment
• What is the preferred use of autoclaving?

  Sterilizing microbiological media and equipment