Post by Microchem Laboratory

These are the top 5 preservative challenge test levers to pull. Background: The USP <51> preservative challenge test uses 3 bacteria, a yeast and a mold. Product is spiked with each microbe individually at day zero, then analyzed at day 14 and 28. Counts for each should go down, not up, over the test. Pull these 5 levers to increase challenge level beyond USP <51>. If you pass, your product is well preserved and your risk of contamination/recall is low. Lever 1 - Re-challenge (inoculate again at day 7, 14, or both) Lever 2 - Add a past contaminant (remember that Burkholderia you isolated from that out of spec product 3 years ago?) Lever 3 - Increase inoculation level (1 million has a nice ring to it) Lever 4 - Sample at day 1, 3, or 7 (well-preserved products kill microbes quickly) Lever 5 - Dilute the product with a bit of water (the microbes will thank you)