Sterility testing: what a pass means.
A sterility test asks one question: does anything grow? Samples go into culture media for at least 14 days, and a pass means no growth was seen. Here is how the USP test works, why it takes two weeks and what a pass can and cannot tell you.
Two broths, two temperatures.
The USP chapter on sterility tests, <71>, uses two culture media. Fluid thioglycollate medium, incubated at 30 to 35 °C, is mainly for anaerobic bacteria but also detects aerobes. Soybean-casein digest medium, incubated at 20 to 25 °C, is for fungi and aerobic bacteria. Both are incubated for at least 14 days, because slow growers need time to show.
Filtration or direct inoculation.
Whenever the product allows it, the sample is passed through a membrane filter with a pore size of 0.45 micrometres or smaller, which traps any microorganisms; the membrane then goes into the media. When filtration is not possible, the sample is added straight to the media, called direct inoculation.
No growth in the sample.
A pass means no growth was observed. The USP chapter is explicit that a pass only shows that no contaminating microorganism was found in the sample examined; the test is not designed on its own to prove a whole batch sterile. The numbers explain why: for batches over 500 containers it tests 2% or 20 units, whichever is less, and if 1 unit in 1,000 were contaminated, a 20-unit sample would catch it only about 2% of the time. A sterility assurance level of one in a million cannot be proven by testing at all; it rests on how the product is made.
Rapid microbiological testing.
Rapid methods aim to cut the 14-day wait. A 2011 evaluation by FDA scientists found an ATP-based method reached results in 5 days against 14, and a 2019 comparison found the compendial test detected 95.7% of 118 challenge organisms within 360 hours, alongside automated blood-culture systems.
Sterility by lot.
Helion's peptide reports from ILS Laboratories include a sterility result: lot 335XA of CJC-1295 + Ipamorelin and lot CU501 of GHK-Cu both read no growth. The bacteriostatic water report covers identity, purity, pH, benzyl alcohol and endotoxin. Endotoxin testing explains the separate test for bacterial endotoxin, and how peptides are tested covers the full report.
Specs and storage by compound.
Questions (6)
What is sterility testing?
A culture test that checks whether living microorganisms grow from a sample, using two media incubated for at least 14 days.
How long does a sterility test take?
At least 14 days of incubation under the USP method; rapid methods can shorten it.
What media are used in sterility testing?
Fluid thioglycollate medium, mainly for anaerobes, and soybean-casein digest medium for fungi and aerobic bacteria.
What does passing a sterility test mean?
No growth was seen in the sample tested. It does not prove that every unit in a batch is sterile.
What is membrane filtration in sterility testing?
Passing the sample through a filter of 0.45 micrometres or smaller to trap microorganisms, then culturing the filter.
Does Helion test for sterility?
Helion's peptide reports include sterility; lot 335XA of CJC-1295 + Ipamorelin read no growth.
Published studies (3)
- Evaluation of growth based rapid microbiological methods for sterility testing of vaccines and other biological products
- Comprehensive Evaluation of Compendial USP<71>, BacT/Alert Dual-T, and Bactec FX for Detection of Product Sterility Testing Contaminants
- The limits of sterility assurance
Citations from PubMed for reference. They describe the compound in the literature, not any Helion lot, and nothing here is guidance on use.