Question

Why is using aseptic techinque important?

Why is a plate containing 30-300 CFU's more useful for calculating the concentration of the original culture tube than a plate with only two colonies?

Answer 1

Aseptic technique is a very important laboratory. Aseptic technique is used for a variety of procedures such as transferring cultures, inoculating media, isolation of pure cultures, and for performing microbiological tests. Proper aseptic technique helps in preventing the contamination of cultures from foreign bacteria inherent in the environment. Example-airborne microorganisms (including fungi).

Only plates (or replicate plates from the same dilution) with 30-300 colonies are counted. This is because the plates which have fewer than 30 colonies give statistically unreliable results, while plates with more than 300 colonies are too crowded to allow all the bacteria to form distinct colonies. Usually, more than one dilution in a series is plated, just to be sure that results in a countable range will be obtained.

This is why 30-300 CFU’s is more useful than a plate with only two colonies.