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This Woburn company is ready to test pot

Medicinal Genomics says its genetic approach is better than traditional culture methods for detecting pathogens on marijuana. SAEED KHAN/AFP/Getty Images/file 2017

Massachusetts is one of 10 states that allows people to use marijuana recreationally. But with legalization comes, well, legislation — including standards for safety testing.

Only one lab has completed the application for a license from the state to test weed for microbial and other contaminants for recreational sales. The Massachusetts Cannabis Control Commission is expected to vote on that application later this month.

But that lab — and the others that may follow — will need tests to conduct their work. Woburn-based Medicinal Genomics claims its tests, which cost about $5 each per sample, have a specificity of 96.3 percent for bacterial contaminants and 99.97 percent for fungal ones. The company also says its genetic approach is better than traditional culture methods for detecting pathogens on marijuana because its species-specific approach allows cultivators to use “good” microbes. (Some, however, are concerned the tests might be too sensitive or fall behind the curve as pathogens mutate.)

Medicinal Genomics’ chief science officer, Kevin McKernan, walked through the what and why of testing weed for microbial contaminants. This interview has been lightly edited for clarity.


How can marijuana get contaminated?

That’s a really good question. I don’t know that we have enough data on that. Aspergillus is pretty ubiquitous in the soil, so that’s possible. There are some people concerned over water contamination with E. coli, that it might be getting into the hydroponic system.

What tests are typically run?

Which test you use depends on the state. You can put the states into two different categories. There’s sort of the California-like regulations that are species-specific. They’re looking for E. coli, Salmonella, and four different Aspergillus species. You really have to use molecular tools to sort those out. And then there are other states that follow the American Herbal Pharmacopoeia, which posted some guidelines on looking for certain numbers of colony-forming units per gram. Massachusetts is one of those states.


In Massachusetts, there are six tests that you have to run — people often call it the six-pack. It’s total aerobic colony count, total yeast and mold, biotolerant gram-negative, E. coli, Salmonella, and coliforms.

How do your tests work?

Ours are all based on PCR. We’re looking for DNA that sits on the plant.

The E. coli and Salmonella are pretty straightforward; I think a lot of labs are using qPCR for that. We look for the species-specific 16S ribosomal sequences.

For Aspergillus and other fungi, we target ribosomal internal transcribed spacer regions, which are conserved. So if there is a mutation in these regions, it will likely change the definition of the species. The mutation would also have to happen in all copies of the ITS region, which is highly unlikely to occur.

Testing marijuana destined for people who may be immunocompromised — people undergoing chemotherapy or people with cystic fibrosis, for example — makes sense. They’re particularly vulnerable to infections. But can stuff on marijuana actually pose a health risk to people who aren’t already ill?

The microbial risk, I think, is the main threat in cannabis. There’s not a lot of evidence of people being adversely impacted by the cannabinoids.

And even the heavy metals and the pesticides are things that accrue over time and can be carcinogenic if you’re healthy, but they don’t create an acute sickness, per se. But we have seen that with the microbes. There was one case of a healthy person getting cryptococcal meningitis in California. Some can give you aspergillosis, which has a 50 percent mortality rate. So the microbial risk is really the main threat in cannabis. There are a few other social things that we have to get our heads around, like driving and testing and whatnot, but the microbes are serious.


Kate Sheridan can be reached at