3.11: Determination of Bacterial Numbers
- Page ID
- 90988
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Plate Counts
Preparation
- sterile TSB in test tubes on hand for E. coli cultures (1 per group)
- TSA plates (4 per group)
- Sterilize:
- microcentrifuge tubes (7 per group)
- tips for pipettes (for pipettes that can dispense 990 μL and 100 μL)
- inoculate sterile TSB in test tubes with E. coli 8-16 hours before lab and incubate at 37 °C (1 per group)
Materials
- sterile microcentrifuge tubes (7 per group)
- sterile tips for pipettes (for pipettes that can dispense 990 μL and 100 μL)
- pipettes for dispensing 990 μL and 100 μL (enough for each group or for two groups to share)
- containers for used pipette tips
- 8-16 hour E. coli cultures in TSB (1 per group)
- TSA plates (4 per group)
- vortex (enough of them for groups to share)
- labeling marker (1 per group)
- spreader tools (1 per group)
- ethanol in squirt bottles
- empty petri plates (1/2 per group)
- Bunsen burners (1 per group)
- strikers (1 per group)
Absorbance Measurements
Preparation
- test tubes with 5 mL sterile TSB (4 per group)
- inoculate sterile TSB in test tubes with E. coli 8-16 hours before lab and incubate at 37 °C (1 per group) - if the plate counts are being done with the absorbance measurements, these are the same cultures used for the plate counts
Materials
- test tubes with 5 mL sterile TSB (4 per group)
- 8-16 hour E. coli cultures in TSB (1 per group)
- pipettes for transferring 5 mL (enough for each group to complete four transfers
- transfer pipettes (5 per group)
- cuvettes
- waste container for E. coli samples emptied from cuvettes
- spectrophotometer set to 600 nm (enough for two groups to share)
- labeling tape (1 per group)
- labeling marker (1 per group)
Creating a Standard Line between Plate Counts and Absorbance
Materials
- graph paper or computers with graphing software (1 per student)
- rulers (1 per student if using graph paper)