Safety regulations and requirements are quickly evolving in the budding U.S. cannabis industry. Microbial testing is now nearly standard in states that have legalized the sale of cannabis for medicinal and recreational use. Here’s why microbial testing is critical for the cannabis industry and how labs are testing for microbial contamination.

Microbial Testing: Why It’s Important

Cannabis testing has emerged as a key aspect of the rapidly growing cannabis industry in the U.S. Testing plays two important roles. First, growers and distributors need testing to accurately determine the potency of their products. And second, cannabis testing detects many different types of contaminants that pose health and safety risks to consumers.

From the seed to the final product, cannabis is exposed to bacteria, fungus, and many other microorganisms. Normally this isn’t an issue. Like the microbiome of our gut, the soil contains many friendly microorganisms that can be helpful to the growth of the plant.

However, certain microorganisms can cause disease. These dangerous microorganisms are called pathogens and it’s why microbial testing is crucial for cannabis products.

Harmful microbial contamination can happen during the growth and production stage or from staff handling the product. Cannabis contaminated with microbial pathogens poses an obvious danger to consumers. For example, Salmonella and certain strains of E. Coli can cause gastroenteritis and diarrhea if ingested. The Bureau of Cannabis Control in the state of California requires microbial testing for all cannabis products.

Using qPCR to Test for Microbes

There two primary methods to test for microbes in a cannabis sample. The traditional gold standard for identifying pathogens is the plating or culture method. This involves incubating your sample in a nutrient-rich medium and looking for pathogen growth.

However, this method is prone to false positives. It can also be hard to detect certain pathogens like the fungus Aspergillus which is difficult to grow in culture medium.

Molecular methods like qPCR have some unique advantages when it comes to identifying pathogenic microorganisms. They provide more rapid results and can identify additional pathogens not detected by culture.

qPCR stands for quantitative polymerase chain reaction. This method allows cannabis testers to detect even small amounts of a pathogen. That’s because qPCR can quantify how much pathogen DNA is present in a sample, making it a precise and highly pathogen-specific method.

qPCR is especially advantageous for cannabis testing in California where state regulations require testing for very specific microbial pathogens. Inhalable cannabis products must be tested for the presence of:

  1. Shiga toxin–producing Escherichia coli 
  2. Salmonella spp.
  3. Pathogenic Aspergillus species A. fumigatusA. flavusA. niger, and A. terreus

Non-inhalable products like edibles only need to be tested for 1 and 2 above.


Microbial testing is important for keeping cannabis consumers safe and healthy. Although culture-based plate testing used to be the gold standard for microbial testing, many cannabis testing labs now favor qPCR as a more pathogen-specific method that gives fast results.

At Encore Labs, our highly trained staff uses qPCR to test for microbial contamination. Contact us today to learn more about our cannabis testing options, including our comprehensive California compliance testing.