Counting Microbial Cells
Microbial cells can be counted directly or cell count plating methods can be used.
In the direct count method a Petroff-Hauser counting chamber is used. This is glass slide that fits on the stage of a microscope. It has a small depression of known volume. There is a grid on the slide. By determining the number of organisms per square in the grid, an estimate of the number of microorganisms can be made.
There are a number of problems with this method.
1) Dead cells cannot be distinguished from live cells.
2) Small cells are difficult to see.
3) Precision is difficult to attain