What is measured
An aerobic plate count measures organisms that form colonies under the selected test conditions. It is useful for baseline checks and comparisons when the sampling and method remain consistent.
Where it fits
Use the count as one part of an agreed quality program, such as ingredient checks, process comparisons or finished-lot monitoring. The result is not a test for every pathogen and is not a sterility result.
Choose the reporting basis
Product samples are commonly expressed on a mass or volume basis. Environmental samples may use a defined area or collected sample. Establish the basis and reporting limit before comparing values.
When a count changes
Review lot history, collection timing, handling and process conditions. A change can suggest a need for more focused testing, but the number alone does not identify the organism or its source.
Related testing & guidance
Technical & service references
Vanguard microbiology service menuFDA: Bacteriological Analytical ManualUSP: General Chapter <61>Source review: November 8, 2026. The agreed method and project scope govern the testing.