'Sterile' on a research peptide: sterility, bioburden and endotoxin are different tests

Three tests that are often blurred together

Product pages for research peptides sometimes use 'sterile', 'sterile filtered' or 'endotoxin tested' as if they were interchangeable quality badges. They are not. Each comes from a different test with a different question, and a pass on one tells you nothing about the others.

A sterility test asks whether any viable microorganisms are present. US regulations for biological products describe the method as one that must be capable of reliably and consistently detecting the presence of viable contaminating microorganisms. [1] Bioburden testing asks how many microorganisms are present at a point in manufacturing; US drug manufacturing rules list it among in-process controls, applied where appropriate. [3] An endotoxin test asks how much bacterial lipopolysaccharide is present, which is a chemical residue rather than a living organism. [5]

What a real sterility test involves

The three main pharmacopoeial sterility chapters, Ph. Eur. 2.6.1 Sterility, JP 4.06 Sterility Test and USP <71> Sterility Tests, were evaluated through the ICH Q4B process and recommended as interchangeable in the ICH regions, with harmonised acceptance criteria. [2] The same ICH annex notes that diluting and rinsing fluids must not have antibacterial or antifungal properties, and that for liquid parenteral preparations of 100 mL nominal volume in batches of more than 500 containers, the chapters are interchangeable when the minimum number of containers tested is 20 or 2 percent of the batch, whichever is lower. [2] Sample size is therefore a defined part of the method, not a detail a seller can leave out.

For licensed biological products, 21 CFR 610.12 requires written procedures that, for culture-based methods, specify the media, growth-promotion checks and the incubation time and temperature, and requires a sample appropriate to the lot size, container size and any inhibitory or preservative content. [1] A positive result fails the lot unless an investigation attributes it to laboratory error or faulty materials, in which case the test may be repeated one time. [1]

The practical consequence for a reader: a sterility result is a statement about a specific lot, tested by a named method, with a defined sample. A sentence on a product page is not a sterility result.

Why sterile filtered does not mean low endotoxin

FDA's inspection guide on bacterial endotoxins describes endotoxins as lipopolysaccharides found in the outer membrane of Gram-negative bacteria and released when the cells die and lyse. [5] It states that endotoxins are not removed by sterilizing or microbiological filters, so reducing microbial levels does not necessarily reduce endotoxin levels, and it notes that sterile devices have occasionally been shown to be contaminated with endotoxins. [5]

That is the key reason 'sterile filtered' and 'endotoxin tested' must be read as separate claims. Filtration can remove organisms; it does not deal with the cell-wall material they leave behind. FDA's question-and-answer guidance on pyrogen and endotoxin testing points to USP chapter <85>, Bacterial Endotoxins Test, and to the gel-clot, photometric and kinetic test methods. [6] Our separate guide on reading an LAL result covers units and limits in more detail.

Why research-use powders usually carry no sterility claim backed by a test

In US drug manufacturing rules, each batch of a drug product purporting to be sterile and/or pyrogen-free must have appropriate laboratory testing to determine conformance, under written procedures. [4] Those rules attach to drug products. A storefront that sells lyophilized peptides as research-use-only material is not presenting its vials under that framework, so nothing obliges it to run a compendial sterility test before using the word sterile. The only way to know whether a test stands behind the word is to see the lot report.

Two current product pages show why reading closely matters. A Peptides EU product page lists a certificate titled 'Sterility' whose description reads 'Independent HPLC testing by Janoshik Analytical'. [7] HPLC is a chromatographic purity method, not a sterility method, so the description alone does not establish that a sterility test was run; ask for the report itself. An Evolve Peptides product page describes the product as provided in a 'sterile glass vial', 'sealed and sterile', and shows an image whose file name indicates an endotoxin certificate. [8] A sterile container and a tested sterile lot are not the same claim, and an endotoxin certificate is not a sterility certificate.

What a certificate must state for a sterility claim to mean anything

Use this as the minimum. If any line is missing, treat the sterility claim as unverified marketing rather than a test result.

Checklist for 'sterile' or 'sterile filtered' marketing

Work through these before treating any microbiological claim as documented.

• Does the claim refer to the container, the filling process or the finished lot? Ask which.
• Is there a lot-specific sterility report, and does its method name match a sterility test rather than HPLC or mass spectrometry?
• Does the report state sample size, incubation and the acceptance criterion?
• If the page says 'sterile filtered', is there also a separate endotoxin result? Filtration does not remove endotoxin. [5]
• Is the endotoxin result expressed in EU with a stated method (gel-clot, turbidimetric or chromogenic)? [5]
• Is the issuing laboratory named, and can it confirm the report number?
• Is any bioburden figure presented as if it were a sterility result? It is not. [3]
• File the reports under the lot number with your receiving records.