ABSTRACT
This chapter provides general information on the various methods used to estimate the number of microorganisms in a given sample. The MPN method is useful in the estimation of low microorganism counts where particulate matter, turbidity is present in the sample matrix, such as in milk, food, water, soil. Turbidimetric methods are used where a large number of microorganisms is to be enumerated or when the inoculum size of a specific microbial suspension is to be determined. The total colony counts obtained in CFU from the incubated agar plates and the respective dilution factor used can then be combined to calculate the original number of microorganisms in the sample in CFU per mL. The plate count method is used primarily in the enumeration of samples with high microorganism numbers or microorganisms that grow well in liquid media. The membrane filtration method is used to concentrate the number of microorganisms from large volumes of liquid sample with low numbers of microorganisms.
