What are a group of microorganisms called?

Answer 1

In the broadest terms, a group of microorganisms can be an ecosystem of its own, or a population. For example the group of microorganisms that inhabit your mouth are the population of your oral cavity. A species is every organism that exhibits the same DNA (within reason, there are so many ways DNA can be mutated) and key features.

The most often time you see a group of microorganisms may be on a agar plate, after incubating the plate you've streaked with bacteria. In this case the groups, or blobs, are called 'colonies'.

While each colony has millions(!!) of bacterial cells in it (hence why you can see it!), they all came from one bacteria. Because we know this we can count the number of colonies and know how many bacteria were originally on the plate, somethings microbiologists call CFU, or Colony-Forming-Units.

Many examples in food and beverage industry involved maximum CFU values per mL of beverage or gram of food for it to pass inspection. This is how it is determined.

Answer 2

There are actually 6 main groups of microorganisms:

Bacteria, Actinomycetes, Protozoa, Algae, Fungi and Viruses.