Why is the level of contamination measured as number of colonies rather than size of colonies?

Question

Thanks again

Answer 1

In theory, if a test is properly done, then each colony will represent one bacterium in the original sample. The size of the colony doesn't tell you much, as it could be affected by the temperature variations in different parts of the incubator space, trivial differences in trace elements in the growth medium, timing differences - each colony would have to be measured at a very specific time - etc. You would have to specifically identify the exact strain of bacteria in each colony and compare against some kind of standard for that particular culture. That would really be hard!