An article appeared in the Cannabis Industry Journal (CIJ, February 8, 2017), titled “Colorado Cannabis Lab Methods Updated for Microbial Testing”. The article called out a bulletin issued by the Colorado Department of Public Health and Environment’s (CDPHE) Marijuana Laboratory Inspection Program on January 30, 2017, regarding updates required for licensed cannabis testing labs. The specific updated method for microbial contaminant testing includes a longer incubation period for yeast and mold testing.
The bulletin was issued after consideration of emerging data regarding the use and effectiveness of the 3M[1] total Yeast and Mold (YM) and Rapid Yeast and Mold (RYM) Petrifilms® for cannabis samples. The CDPHE concluded that 48 hours was not a sufficient incubation period to obtain accurate results. “Based upon the CDPHE review, marijuana/marijuana products require 60 to 72 hours of incubation per the manufacturer’s product instructions for human food products, animal feed and environmental products.” The CDPHE said they determined it was necessary to increase the incubation period based on data submitted from several labs, along with a paper published in the Journal of Food Protection.
As reported in the Journal of Food Protection, Vol. 79 (1), pp. 95 – 111 for the 3M rapid yeast and mold plates and 3M yeast and mold plates (Table 1 is reproduced for only the RYM and YM results):
[1] 3M is a registered trademark of the Minnesota Mining and Manufacturing Company, 3M Corporation Delaware 3M Center Saint Paul, Minnesota.Table 1. Number and percentage of foods and food ingredients negative for yeasts plus molds when samples were plated and incubated for 48, 72, and 120 hr at 25oC
| Number (%) of samples negative (< 1 log CFU/g or mL) for colony formation1 | |||
| Microorganism | Incubation Time (hr) | RYM | YM |
| Yeasts | 48 | 21 (61.8) | 26 (76.5) |
| 72 | 8 (23.5) | 13 (38.2) | |
| 120 | 6 (17.6) | 7 (20.6) | |
| Molds | 48 | 29 (67.4) | 32 (74.4) |
| 72 | 6 (14) | 7 (16.3) | |
| 120 | 2 (4.6) | 2 (4.6) | |
| Yeast + Mold | 48 | 31 (55.4) | 41 (73.2) |
| 72 | 6 (10.7) | 8 (14.3) | |
| 120 | 2 (3.6) | 1 (1,8) |
1Values indicate the number (percentage) of samples out of 34 (yeasts), 43 (molds) and 56 (yeasts plus molds) foods and food ingredients in which no yeasts, molds, or yeasts plus molds, respectively, were detected
Therefore, the probability of a false negative is higher if the lab reports at the 48 hour count, as opposed to the 72 hour count.
