Microbial Enumeration
Microbial Enumeration Tests (USP <61>) and Tests for Specified Microorganisms (USP <62>)
What a definition is not
A definition is SPEQ’s plain-language decode of how a term is used in practice, cited to the documents that define it. It is a practitioner reference, not legal or regulatory advice, it does not replace the definition in the source, and where a regulator’s wording differs the regulator’s wording governs.
Compendial tests applied to non-sterile pharmaceutical articles, raw materials, excipients, and components: <61> quantifies total aerobic microbial count and total combined yeasts/moulds count, while <62> tests for the absence of specified objectionable organisms such as E. coli, Salmonella, and Staphylococcus aureus, selected based on the product’s route of administration and patient population.
Acceptance criteria are set per the product’s microbiological attribute category — oral, topical, mucosal, and inhaled dosage forms carry progressively tighter total-count and objectionable-organism limits reflecting the route’s infection risk.
Unlike sterility testing, these methods do not require an aseptic environment for sample preparation, but they do require method suitability (validation) to confirm the product itself does not inhibit microbial recovery.
Water activity, preservative efficacy, and raw-material bioburden all feed into the risk assessment that determines testing frequency and acceptance criteria for a given non-sterile product.
- —Applies to non-sterile products, unlike the sterility test.
- —<61> counts total aerobic microbes and yeasts/moulds; <62> screens for specified objectionable organisms.
- —Acceptance criteria depend on route of administration and intended patient population.
- —Requires method suitability testing to rule out antimicrobial inhibition by the product matrix.
USP <61>; USP <62>; Ph. Eur. 2.6.12; Ph. Eur. 2.6.13
Frequently asked questions
What does Microbial Enumeration stand for?
Microbial Enumeration stands for Microbial Enumeration Tests (USP <61>) and Tests for Specified Microorganisms (USP <62>).
What is Microbial Enumeration?
Compendial tests applied to non-sterile pharmaceutical articles, raw materials, excipients, and components: <61> quantifies total aerobic microbial count and total combined yeasts/moulds count, while <62> tests for the absence of specified objectionable organisms such as E. coli, Salmonella, and Staphylococcus aureus, selected based on the product’s route of administration and patient population.
Which regulations cover Microbial Enumeration?
USP <61>; USP <62>; Ph. Eur. 2.6.12; Ph. Eur. 2.6.13