Measuring Microbial Growth

1
Measuring Microbial Growth

• Lab 5

2
Measuring Cell Growth

• Number of Cells per milliliter of liquid
• cells/ml
• Bacterial cultures contain millions of cells
• Direct Vs. indirect counts
• Direct Counts mean actually counting cells
• More accurate, but takes a lot longer
• Indirect Counts mean estimating the number of
  cells based on turbidity in liquid or dry weight.
• Less accurate, but quick
• Total Count vs. Viable count
• Total count?all cells in a culture
• Viable count?only live cells

3
Turbidity Method

• Spectrophotometer
• Measure transmittance
• Amount of light going through culture
• Transmittance is inversely proportional to
  turbidity (cell concentration)
• As turbidity increases cell number increases and
  transmittance decreases
• Indirect and Total Count

4
Turbidity and Transmittance
5
Plate Counts

• Direct Viable counts
• The idea is to evenly spread the culture across a
  plate and count the colonies
• Each colony represents a cell in the original
  culture.
• Problem If we have a culture that has 1x106
  cells/ml and we put 1 ml on the plate will we
  have isolated colonies?

6
Plate Count

• We must dilute first
• If we put 1ml of culture into 9 ml of sterile
  media we have performed a 1/10 serial dilution
  (SD)
• Formula SDAT/TV
• ATamount of culture transferred
• TVTotal volume after transfer (1ml 9 ml)
• What if we did 5 serial dilutions on that culture
  that had 1 x 106 cells/ml