What is the role of statistical method in microbiology?

The role of statistics is enormous in microbiology. I believe every school would require at least one or more courses in "biOStatistics", which is the general application of statistical methodology, including planning experiments, drawing inferences, assessing correlations or dependencies with data.

From wikipedia on biOStatistics (see related link)

The science of biOStatistics encompasses the design of biological experiments, especially in medicine and agriculture; the collection, summarization, and analysis of data from those experiments; and the interpretation of, and inference from, the results.

There is a related field, bioinformatics, which is studied as part of molecular Biology, and genetics. This field uses more the probability theory in analyzing genetic code. One of the uses of bioinformatics is attempting to reconstruct the biological evolution in plants and animals.

See related link on bioinformatics.