There are many situations in which the number of bacterial cells in a population must be determined.
For example, microbiologists monitor the number of bacteria in our food and water in order to ensure
that it is safe for consumption. Water is also monitored to determine whether it is safe for swimming or
the harvesting of seafood. Healthcare providers need to monitor the concentration of bacteria in a
patient’s body fluid while the patient is undergoing antibiotic therapy for an infection. Because bacterial
populations may contain thousands to millions of individual cells, most methods of counting them are
based on direct or indirect counts of very small samples taken from the population.