Challenges to Microbiological Enumeration

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Analytical Cannabis

Speaking at the Analytical Cannabis Expo East Online 2020 in October, Mike Esposito, Scientist I at MCR Labs presented his talk on microbiological testing of cannabis. Humans have been enumerating microorganisms since 1878, and in the nearly 150 year history of enumeration, incredible new techniques and technologies have been implemented to both simplify and increase the accuracy of our microbial counting methods. While these techniques range in complexity from counting cells under a microscope to quantifying DNA extracted from a microbe, they all have their own distinct advantages and challenges. In this talk we will take a look at historical strategies, contemporary approaches, and up and coming technologies that we can look forward to. We will discuss shortcomings of traditional methods, like the difficulties of counting dense colonies on a plate and the slow turn-around of test results due to incubations, as well as describing the advantages of these techniques, such as robust validation and decades of implementation that make these techniques the “golden standard”. Additionally, we will look at new technologies like micro-arrays and qPCR that aim to eliminate issues with turnaround time and off-target ennumeration, but come with their own host of issues such as highly variable extraction efficiencies and the rarely discussed topic of copy number variation in some gene targets. Lastly, we will look at adaptations to culture-based and PCR based methods, such as the widely used most probable number technique, and the up and coming droplet digital PCR technology that will look to combine the speed of qPCR with the accuracy of most probable number testing.