8: Summary

In this module you have learnt some of the techniques that can be used for counting bacterial cells.

  • The direct count, which uses a microscope to detect and count bacterial cells that have been loaded on a slide or a counting chamber
  • The spectrophotometric method, which uses a spectrophotometer.  This method doesn’t exactly count the bacteria, but it does measure how much light is absorbed by bacterial cells in suspension, and based on that, a standard curve can be used to decide how many bacteria there are.
  • The viable plate count, which unlike the other two techniques, allows you to determine how many bacterial cells are alive in a bacterial population.

The next module “Viable Plate Count, or How to Count to a Million“ will show you all the steps and calculations involved in performing a viable plate count by using a serial dilution technique.

Learning Outcomes

Now 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


If you want a printer-friendly version of this module, you can find it here in a PDF document. This printer-friendly version should be used only to review, as it does not contain any of the interactive material, and only a skeletal version of problems solved in the module.