Final answer:
A colony-forming unit is one or more cells that reproduce to form a pile of identical cells, known as a colony, on an agar plate. The plate count is a standard method used to estimate bacterial numbers in samples, and results are given in CFUs per mL.
Step-by-step explanation:
What is a colony-forming unit?
A colony-forming unit (CFU) refers to one or more cells that give rise to an assemblage of identical cells. A single cell or a group of identical cells lands on a nutrient medium, like an agar plate, and reproduces to form a visible pile of bacterial cells, known as a colony. Each of these colonies originates from a CFU and consists of clones of the original cell(s). This is instrumental in obtaining pure bacterial cultures in microbiology.
Estimating Bacterial Numbers
Microbiologists frequently use the plate count and membrane filtration methods to estimate bacterial numbers in water samples. The plate count method involves spreading a known volume of a water sample over the surface of an agar plate, incubating it, and then counting the colonies formed to calculate the number of viable bacteria present in the sample. These results are expressed as CFUs per milliliter (CFU/mL).