Read my page on types of pipets . Suppose 125 colonies grow in the petri plate. 250,000,000 bacteria per milliliter in the original sample. Beginners usually assume each colony grew from a single bacteria, but experts prefer say each colony originated from a colony-forming unit. Dead bacteria do not form colonies.
Some bacteria occur as single cells.
Other species hang together in chains or clumps of 2 or more bacteria. A piece of dirt with 10 bacteria on it will form a single colony. Molecular biologists do everything with as much precision as possible. Therefore, they prefer to work with bacteria which do not form chains or clumps. Other Methods for Counting Bacteria Counting Chambers Counting chambers automaticly fill with a certain volume.