INHIBITION & DESTRUCTION OF MICROORGANISM BY PHYSICAL AGENTS

• Sterilization


  All forms of microbial life including bacterial spores are killed

  
• Disinfection


  Pathogenic organisms but not necessarily all microorganisms or spores are destroyed

  
• Moist heat under steam pressure

  1. Kills by coagulation of proteins including enzymes and structural protein

  2. Autoclave at 121°C at 15psi for 15-20 minutes to sterilize medical liquids and instruments

  3. Autoclave at 132°C at 15psi for 30-60 minutes to sterilize infectious medical waste
• Quality control (QC) for sterilization


  • Done to ensure sterilization is effective
  • Uses Bacillus stearothermophilus in vials or spore-strip sets incorporated in autoclave
• Dry heat


  1. Causes protein oxidation

  2. Hot air sterilization using ovens at 160-180°C for 1.5-3 hours

  3. Used for sterilization of glassware for lab use
• Nutrient broth


  • Culture medium used for this activity
  • Turbidity indicates growth of microorganisms
• Procedure


  1. Transfer impregnated filter paper into nutrient broth and incubate

  2. Immerse inoculated nutrient broth in boiling water bath for 30 minutes

  3. Immerse inoculated nutrient broth in 80°C water bath for 30 minutes

  4. Transfer autoclaved and hot air subjected impregnated filter papers into nutrient broth
• Observation is indicated as turbid or clear
• Interpretation


  Bacteria were killed or bacteria were not killed

  
• Lactose broth with Durham's fermentation tube

  • Selective culture medium
  • Andrade's indicator turns pink in presence of acid
  • Fermentation of lactose produces acid and gas
• Evidence of bacterial growth after incubation includes turbidity, presence of gas, and change in pH
• Disinfectants used


  • Lysol
  • 1:1000 Mercuric Chloride
  • Tincture of Iodine
  • 70% Alcohol
  • 3% H2O2
• Procedure for testing disinfectants

  1. Transfer 1 mL of cultured E. coli to 10 mL of disinfectant

  2. Transfer inoculum from mixture to Lactose broth tube at 5, 10, 15, and 30 minutes

  
• Reading of the result notes the presence of gas inside the Durham's fermentation tube
• Interpretation of the result

  Bacteria were killed or bacteria were not killed at the specific time