Accurate and effective methods for cannabis testing are crucial for ensuring the safety of both medicinal and recreational cannabis users. While the American Herbal Products Association and the American Herbal Pharmacopoeia offer guidelines on how to conduct cannabis cultivation, processing, and dispensing in order to minimize risks from contamination, proper testing methods are needed to quantify the risk presented by contamination.
In the absence of any federal safety regulations and procedures from either the FDA or the USDA, individual states are responsible for implementing their own cannabis testing procedures. The two most common microbiological testing methods used are traditional culture methods (TCM) and quantitative polymerase-chain-reaction (qPCR) analysis.
TCM is considered by many as the go-to standard for detecting harmful microbes. It is relatively simple and straightforward to carry out, and it is possible to purchase sample-ready culture medium systems designed for common processes such as total yeast and mold tests. However, qPCR has gained prevalence as a more targeted approach to testing. It works by amplifying sections of DNA or RNA present in the sample that are characteristic of the compounds or microbes being tested for. qPCR has become more common as foodstuffs and biological materials with short shelf lives often cannot be analyzed using TCM, requiring a more rapid testing approach.
As cannabis testing is not federally regulated, states are free to mandate the use of either of these analytical methods to examine cannabis samples. Each method has its own pros and cons that must be considered to better understand their suitability and compatibility.
One of the biggest advantages qPCR has over TCM is the speed at which results are produced. Carrying out TCM can take between 24-48 hours depending on the time required to grow and analyze the culture. In comparison, qPCR runs often last only two hours from start to finish and can be done in as little as 40 minutes on some instruments.
Both methods require a certain amount of experience in order to interpret their respective outputs. Interpretation of qPCR results was previously difficult, but with the creation of genomic databases of sequences found from previous runs, it is getting easier.
Another factor to bear in mind with qPCR is that even though a DNA sequence may be detected, it may not actually be expressed. This presents a potential challenge as samples could fail testing as contaminated based on qPCR analysis alone, even if no toxin is being produced.
Similarly, TCM is not a perfect method. Many types of microbe do not culture well and will be underrepresented by this method. This can have potentially dangerous consequences when the bacteria being underrepresented are dangerous to humans.
Due to its ease of use and general accessibility, qPCR is growing in popularity as a method for microbiological testing. It is able to detect specific microbial risks through DNA analysis and does so with less distortion to the final results, hence creating a far more accurate picture of the microbial environment present on the cannabis material.
These findings also have implications outside the cannabis industry, as TCM is still one of the major methods being used to monitor the quality and safety of other foodstuffs. It is important to focus on using our increased understanding of crop microbiomes across industries to improve cultivation, handling, and processing methods.
