3M™ Petrifilm™ Rapid Yeast and Mold Count Plate for the Enumeration of Yeasts and Molds in Dried Cannabis Flower: AOAC Official Method(SM) 2014.05

BACKGROUND: The 3M(TM) Petrifilm™ Rapid Yeast and Mold Count (RYM) 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 RYM Plate was validated for the enumeration of yeast and mold in dried cannabis flower through the AOAC Emergency Response Validation process. METHODS: The performance of the 3M Petrifilm RYM Plate was compared to dichloran rose bengal chloramphenicol (DRBC) agar. Matrix data were normalized by log(10) transformation and performance indicators included repeatability, difference of means, and inclusivity/exclusivity. RESULTS: These studies demonstrated the 3M Petrifilm RYM Plate method detects and enumerates yeasts and molds from dried cannabis flower at low, medium, and high contamination levels. The average log counts at 25 or 28°C for 60 to 72 h were equivalent to the average log counts of the DRBC reference method at low, medium and high levels. In strain studies, all 71 yeasts and molds tested produced typical colony morphology on 3M Petrifilm RYM Plates. Of the 32 non-target bacterial strains tested, none were detected on 3M Petrifilm RYM Plates. CONCLUSION: The 3M Petrifilm RYM Plate is a reliable method for the enumeration of live yeast and mold in dried cannabis flower. HIGHLIGHTS: The 3M Petrifilm RYM Plate allows for rapid detection of yeast and mold within 60 to 72 h of incubation. Up to 40 sample-ready plates can be stacked during incubation to save space.