USP <71> Sterility Testing Explained

Why appearance is not enough

A vial can look clean while containing microorganisms. A sterility test examines selected samples for growth under defined conditions. Chemical purity and a clear solution do not supply that information.

The consequences for research are real: viable microorganisms can overgrow a cell culture, change its chemistry and make results unreliable or impossible to repeat. A contaminated experiment can look like a genuine finding until someone tries to reproduce it.

What happens during the test

The laboratory uses an appropriate procedure such as membrane filtration or direct inoculation, with culture media, incubation and controls. USP <71> uses an extended incubation period, generally at least 14 days under its stated conditions. A quick visual check is not equivalent to this procedure. USP: microbiological testing standards.

The method must be suitable for the sample. If the material inhibits growth, the laboratory needs to establish that the procedure can still recover the organisms used to challenge it.

Interpret the finding carefully

Why it cannot guarantee every vial

FDA explains that microbial contamination may be unevenly distributed and a passing sample test is not a substitute for contamination controls. The sampling plan, manufacturing conditions and container integrity all matter. FDA: limitations of sterility sampling.

Sterility and endotoxin remain separate

A no-growth finding concerns viable microorganisms detectable by the procedure. Endotoxin is bacterial material that may remain after organisms die. A sterility result therefore cannot fill a missing endotoxin result.