Plate count agar

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Plate count agar (PCA) is a microbiological growth medium commonly used to assess or to monitor "total" bacterial growth of a sample. Different mixes of materials are used in different media, but a common example is straw yellow in colour, and tends to be used to give an estimation of specific bacterial species growth in a specific sample. Plate count agars contain a limited set of food resources as compared to the thousands of foods present in all but the most limited natural environments. Less than 0.01 to 0.001% of the actual species of bacteria or fungi present in natural habitats can grow on any plate count medium. All media used for plate count methods are severely restrictive. consider that plate agar is incubated at one temperature in the lab, one moisture, one humidity, limited mineral availability in the medium, and a lid is placed on the plate during growth of the microorganisms. Oxygen in the atmosphere in the limited environment in the plate is quickly reduced. As many human and plant pathogens are facultative or strict anaerobes, plate count methods are useful for growing specific, known habitat bacterial and fungal species, but are not appropriate for growing the full diversity of organisms present in environmental samples.