A CANNABIS PRODUCT COULD HAVE 9,000 COLONY FORMING-UNITS
( CFUs ) per gram of a pathogenic Aspergillus species and still “ pass ” under some states ’ medical marijuana limits .”
The route of administration matters , and that fact makes this type of screening inadequate for marijuana products that are generally inhaled . The traditional methods for enumerating total yeast and mold counts ( TYMC ) involve “ plating ” the samples on nutrient-rich media that supports growth of general yeast and mold fungi . The plates are then counted for yeast and mold colonies , called “ colony-forming-units ” ( CFUs ), and the result represents the total fungal bioburden in the sample . Nobody wants moldy cannabis and consumers should not have to think twice about that being a possibility . The TYMC provides marijuana consumers some level of assurance the products they buy have a reasonable upper limit of naturally occurring yeast and mold , which are unavoidable for marijuana or any other botanical product . But , when implemented without screening for toxic Aspergillus species , the TYMC data are incomplete — and potentially dangerously deceiving . That ’ s because with culture-based methods , it is nearly impossible to visually distinguish between species of Aspergillus using culture plate techniques . A . flavus , A . fumigatus , A . niger ( brasilliensis ), and A . terreus are known to be infectious in humans and may result in significant health complications — including the colonization of lungs , where they can reproduce and grow into “ fungal balls ” that live and thrive in the marijuana user ’ s lungs .
On the contrary , there are many microbes that are beneficial and approved for use in cannabis horticulture but are benign to humans . These microbes , like rhizobia fungi , might grow on yeast and mold plate counts , giving an otherwise undue failure . At the same time , a cannabis product could have 9,000 colony-formingunits ( CFUs ) per gram of a pathogenic Aspergillus species and still “ pass ” under some states ’ medical marijuana limits — the “ recommended ” standard set forth in the American Herbal Products Association ’ s early , highly influential , but nonetheless incomplete and , today , outdated Cannabis Inflorescence monograph published in 2014 .
Moving Beyond Plating Samples
It ’ s time to move beyond “ plates .” Molecular methods — quantitative polymerase chain reaction ( qPCR ) testing ( a type of the broader category of PCR testing that checks DNA profiles of target organisms like Aspergillus ) has been commercially available to cannabis labs at reasonably affordable prices for several years now and has been an integral part of the medical laboratory world for decades . Indeed , PCR , invented by Dr . Kary Mullis in the 1980s , led to a Nobel Prize and what we know today as the “ DNA test .” There are several types of PCR assays targeting DNA and RNA . The DNA variants generally involve amplifying a DNA signature in the “ target ” organism of interest — more specifically , a known DNA segment or sequence that is unique to the target organism or species . This aspect of PCR gives it remarkably high specificity for the target organism while excluding background noise from off-target species . Bottom line , if Aspergillus is identified in a sample , the odds of a “ false positive ” are low , and the cannabis batch from which the sample was taken is almost certainly contaminated ( assuming no accidental contamination of the sample between the point of sampling and the point of testing ). Those batches that fail are a threat to public health and safety , and the number of “ false ” failures (“ failing ” marijuana that was not truly contaminated , and was otherwise fit for consumption ) is low — meaning cultivators and processors face nearzero risk of being forced to destroy or remediate “ failed ” batches . The risk of loss of harvest batches , driving up costs for cultivators , processors , and consumers is always a factor that must be considered . As a recent study pointed out , “ losses inflicted by destroying cannabis that fails testing is a major component of overall costs .”
38 Maximum Yield