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

The dilemma of the dead cell

So far we have looked at one relatively hard way (Microscopic Direct Count) and one easy way (Spectrophotometer) to quantify the bacterial load in the water. But both ways share a big problem ... the problem of the dead cell.

If you were counting, say, cats ... this wouldn't really be a problem. A dead cat and a live cat are generally not easily confused. If in doubt, you could poke the cat, and you would know for sure. However, bacterial cells are much less lively than cats. Yes, there is plenty of stuff going on inside, but in general you're not going to see that from the outside. Under a microscope, cells that are alive and cells that are dead look very similar most of the time. And to a standard spectrophotometer, live and dead cells look exactly alike.

Based on the dilemma of the dead cell, which would you predict?

Direct count and spectrophotometer will...?

If we care about getting the number of live cells correct, we need a better way...