Table of Contents

• 1: Recap the story
• 2: Count them all?
• 3: Direct count
• 4: Light scatter (spectrophotometer)
• 5: The dilemma of the dead cell
• 6: Viable plate count
• 7: Comparison of methods
• 8: Summary

Learning Outcomes

When you have completed this module, you should be able to:

• Compare the advantages and disadvantages of direct counts, absorbance and plate counts as methods for enumeration of bacteria

Recap the story

Remember Matt, who went on a surfing holiday and came down with severe diarrhea? Matt, who is lying in hospital with a drip in his arm?

The doctor has diagnosed cholera and is trying to work out the source. Oysters are suspected as the source of Matt’s infection and samples of both the local oysters and the water around the oyster farm have been collected for testing. When the lab does the diagnostic tests, the oysters test positive for Vibrio cholerae (the bacterium that causes cholera). Now the authorities are worried that the bacterium is present in the water where the oysters are growing and they head out to collect samples. They want to know how many Vibrio are present in the water.

But how?