3M™ Petrifilm Yeast and Mold Count Plate for the Enumeration of Yeasts and Molds in Dried Cannabis Flower: AOAC® Official Method 997.02

Background: The 3M™ Petrifilm™ Yeast and Mold (YM) Count Plate is a sample-ready culture medium system which contains nutrients supplemented with antibiotics, a cold-water-soluble gelling agent, and an indicator system that facilitates yeast and mold enumeration.

Objective: The 3M Petrifilm YM Plate was validated for enumeration of yeast and mold in dried cannabis flower through the AOAC Emergency Response Validation process.

Methods: The performance of the 3M Petrifilm YM Plate was compared to that of Dichloran Rose Bengal Chloramphenicol (DRBC) agar. Matrix data were normalized by log10 transformation and performance indicators included repeatability, difference of means, and inclusivity/exclusivity.

Results: These studies demonstrated the 3M Petrifilm YM Plate method detects and enumerates yeasts and molds from cannabis flower at low, medium, and high contamination levels, and the average log counts at 20-25 °C for 5 days were equivalent to the average log counts of the DRBC reference method. In strain studies, 59 out of 60 yeasts and molds produced typical colony morphology on 3M Petrifilm YM Plates. Of the non-target bacterial strains tested, 38 out of 39 strains were not detected on 3M Petrifilm YM Plates.

Conclusions: The 3M Petrifilm YM Plate is a reliable method for the enumeration of live yeast and mold in dried cannabis flower.

Highlights: The 3M Petrifilm YM Plate allows for detection of yeast and mold within 5 days of incubation. The sample-ready plates can be incubated at 20-25 °C and can be stacked up to 20 plates, thus providing user flexibility and saving incubator space.