Trying to understand USP <64> for microbial contaminant testing of a Lactobacillus acidophilus probiotic
Hi all, hoping to get some insight from people who’ve worked with probiotic microbial testing in pharma.
I’m currently trying to interpret USP <64> for a Lactobacillus acidophilus product. I’m okay with the specified microorganisms part, but I’m unsure about the contaminant testing side.
For the "total yeasts and molds" test, we have performed microbial limit testing following USP <61>, using SDA at 23°C for 5 days and have gotten TNTC pinpoint colonies. We think they could be the L. acidophilus probiotic rather than yeast/fungi, but we're not sure. Negative control is clean. What did we do wrong here? Should we have added an antibiotic to the SDA? If so, what and how?
I’m also unsure about the “non-lactic acid bacteria” test. Is it basically a TAMC-type concept for probiotics? USP <64> refers to ISO 13559, and from reading it, it seems like sugar-free agar is used, but I’m not sure I’m interpreting it correctly.
Would really appreciate any advice or clarification from anyone familiar with this area. Thanks!