lab 11

• Physical Methods


  UV, filter
• Chemical Methods


  disinfectants, antiseptics, soaps, antimicrobials
• sterilization


  destroys all microbes, including spores
• sterilization example


  Autoclave
• antiseptic


  reduction of # microbes in living tissues
• disinfection


  destroying microbes in inanimate objects
• UV


  modifies DNA covalent bond with thymine dimers
• direct method


  count viable cells that reproduce to form colonies
• indirect method


  counting cells includes measuring turbidity, metabolic activity, and dry weight
• countable range of colonies

  30-300
• Quebec colony counter


  64 large sqaures
• Series of dilutions


  1/10 or 1/100
• formula


  # CFU (colonies)(1/Amount Plated)(1/dilution factor) = # CFU/ ml original sample
• serial dilutions prepared by

  pour plate method or spread plate method
• Pour Plate Method


  samples embedded in the agar useful for anaerobic or microaerophilic requirements
• Spread plate method


  limited only grow aerobic cultures
• 0.1 ml


  1/10
• 0.01 ml


  1/100
• How to count in Quebec colony counter?

  in three large squares and use average #
• results reported as


  CFU/ml
• spectrophotometer


  used to determine turbidity (cloudiness) by measuring the amount of light that passed through cells
• false


  filtration acts by killing all microbes
• How does the chemical method of microbial growth negatively affect bacteria?


  denatures enzymes/protein and disrupts cell membrane
• two categories of controlling microbial growth


  cell wall or cell membrane or protein