Lab One

• Different pipettor sizes

  • P20
  • P200
  • P1000
• Which two pipettors use smaller tips?

  P20

  P200
• Which pipettor uses larger tip?

  P1000
• What is a standard method for isolating microorganisms?

  streak plate isolation
• Streak Plate Isolation Method

  • sterilize metal loop until red
  • after cool, dip loop in bacteria
  • draw loop across surface of agar plate
  • flame loop again and cool
  • repeat for 3 streaks (flame and cool inbetween)
• Two ways to count bacteria

  1. optical density
  2. plate counts
• Optical Density

  • use absorbance of 600 nm light with spectrophotometer
  • measures concentration of dead and living cells
  • 1.0D (600) = 10^9 cells/mL
• Purpose of plate counts

  • determine concentration of living bacteria in sample
  • provides countable number of colonies on a plate
• Plate Count Method (Visual Count)

  • serial dilutions
  • plate with spreader certain dilutions
  • compare number after incubation at 30-37C
• Dilution Equation

  Dilution = V stock / V total