Peptide Endotoxin and Sterility Testing Explained (LAL & USP)

Two separate questions

Sterility and bacterial endotoxin tests answer different analytical questions. A sterility test seeks viable microorganisms under defined culture conditions. A bacterial endotoxins test detects or quantifies endotoxin from gram-negative bacteria. Because nonviable bacterial material can remain after organisms are killed, the tests are not substitutes for one another.

LAL and recombinant Factor C

USP <85> describes bacterial endotoxins testing with Limulus amebocyte lysate (LAL), including gel-clot, turbidimetric and chromogenic techniques. The applicable limit and reporting units depend on the article, route and method context; a report should state its specification and method.

USP <86>, Bacterial Endotoxins Test Using Recombinant Reagents, covers recombinant Factor C and recombinant cascade reagents. It became official on May 1, 2025, but USP currently treats it as an alternative method unless an individual monograph specifies it. It supplements rather than replaces USP <85>.

The European Pharmacopoeia published chapter 2.6.32 for recombinant Factor C in Supplement 10.3; EDQM states that implementation took effect on January 1, 2021. Product-specific fitness for purpose still has to be demonstrated. Earlier wording that gave July 1, 2021 as the effective date was incorrect.

USP <71> sterility testing

USP <71> uses Fluid Thioglycollate Medium and Soybean–Casein Digest Medium and specifies incubation for not less than 14 days under the chapter's stated conditions. Method suitability matters, particularly when a product can inhibit microbial recovery.

A passing result means no contaminating microorganism was found in the sample examined under the test conditions. It does not by itself prove every unit in a batch is sterile, and it does not establish endotoxin status. Neither sterility nor endotoxin testing makes a research-use-only material suitable for human or veterinary use.