Tag Archives: A. fumigatus

AOAC Accreditation: Why Third-Party Approval Matters More Than Ever

By Anthony Repay
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When people have to make important decisions, we often consult a third party to increase our knowledge and confidence in a product. For instance, when choosing a car, an individual may weigh heavily on safety ratings and other awards from organizations such as Consumer Reports. These awards are often boasted and a heavy focus in car commercials because it tells the consumer that a third party has deemed their car valuable to own. For more than 100 years, the Association of Official Agricultural Chemists (AOAC® International) has operated in this exact manner, and has set the bar and guidelines for testing in the cannabis industry through its special program called the Cannabis Analytical Science Program, also known as CASP.

The CASP program is designed to develop standards and validation guidance to evaluate testing methods, as well as the methods’ ability to detect the target organism or compound on the cannabis matrix. With the addition of new states permitting the legal sale of both medical and adult use cannabis and no federal governing body overseeing testing regulations, the value of AOAC cannot be understated, as these guidelines allow cannabis testing laboratories to have their own third-party reference to look to when choosing a compliant testing method to implement in their laboratory.

AOAC was founded in 1884 by the US government as the standard setting body in the country and, in 1991, became an independent association known as AOAC International, with a goal of building a reputation as an international, consensus-based standard-setting body and a conformity assessment organization in analytical sciences. As an independent third-party resource, AOAC has the Performance Tested Methods’ (PTM) and Official Methods of AnalysisSM (OMA) programs for certification of analytical testing methods in both biology and chemistry.

If analytical methods, including proprietary test kits, are deemed acceptable, AOAC provides approved certification, their seal of approval that the method works as designed. Though multiple factors are considered to determine if AOAC approval is given; accuracy and precision of the method are among the most important. For example, when validating a cannabis method for microbiology, AOAC will contract an independent testing facility to conduct a series of tests with known spiked samples to measure the recovery limit of the target microorganism. This allows the organization to determine if the method is sensitive enough to be named an AOAC-approved method through either the PTM or OMA conformity programs. Another way of ensuring the validity of results is by conducting an inclusivity and exclusivity study on a method. In this type of experiment, target organisms are tested while also spiking with non-target organisms to see if there will be a high rate of false positives.

In cannabis, discussions have grown surrounding testing of four strains of Aspergillus, which are A. terreus, A. flavus, A. fumigatus and A. niger. By spiking cannabis with one of the four Aspergillus strains and on a separate sample with a non-target Aspergillus strain such as A. clavatus, it ensures that only the target strains are being recognized and recorded on the method being tested.

This methodology limits the likelihood of unconfirmed positives occurring, ensuring the validity of the results. Of course, when a method is undergoing an actual AOAC evaluation for approval, the testing requirements for both the sensitivity and inclusivity/exclusivity experiments are much more thorough than the explanation above.

Regardless of which AOAC-approved method you select, you can feel confident that most of the “heavy-lifting” is done and that the method is accurate and precise enough to implement in a cannabis testing facility. In turn, the cannabis testing laboratory then only needs to complete their own internal method verification to ensure the method works with their processes, people, environment and product, but on a much smaller scale and aligns with state regulations.

labsphotoOn a consumer safety level, AOAC-approved methods are designed to keep cannabis consumers safe. Whether they are an adult using cannabis or medicinal cannabis patient, the product that is being sold should be held to the highest safety standards. By having a laboratory that is utilizing an independently approved AOAC method, an additional layer of confidence is achieved that the product being consumed is safe. This ultimately limits the number of costly recalls from dispensaries and minimizes risk to consumers. At the end of the day, cannabis testing laboratories want to keep the public safe and it is our job to do so. This means implementing these independently approved methods from agencies such as AOAC at various touch points in the seed to sale cycle to ensure the data is validated and reliable.

Overall, just as it is equally important to get a non-biased and reputable third-party approach to your automobile search, a scientist that is responsible for choosing methods in their cannabis compliance laboratory should also consider these third-party approvals. As a scientist, the goal every day is to report accurate data to help the client and the consumer equally. The cannabis compliance laboratories are the last line of defense in preventing harmful or contaminated products from getting into the marketplace and any extra assurance we have with our testing methodology is always encouraged. Ultimately, AOAC’s work is important and their standard of quality and safety is a must-have in the cannabis laboratory.

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How Do You Know You’re Right? qPCR vs. Plating

By Dr. Sherman Hom
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Cannabis testing to detect microbial contamination is complicated. It may not be rocket science, but it is life science, which means it’s a moving target, or at least, it should be, as we acquire more and more information about how the world we live in works. We are lucky to be able to carry out that examination in ever increasing detail. For instance, the science of genomics1 was born over 80 years ago, and just twenty years ago, genetics was still a black box. We’ve made tremendous progress since those early days, but we still have a long way to go, to be sure.

Much of that progress is due to our ability to build more accurate tools, a technological ladder, if you will, that raises our awareness, expertise, and knowledge to new levels. When a new process or technology appears, we compare it against accepted practice to create a new paradigm and make the necessary adjustments. But people have to be willing to change. In the cannabis industry, rapid change is a constant, first because that is the nature of a nascent industry, and second because in the absence of some universal and unimpeachable standard, it’s difficult to know who’s right. Especially when the old, reliable reference method (i.e. plating, which is basically growing microorganisms on the surface of a nutritional medium) is deeply flawed in its application to cannabis testing vs. molecular methods (i.e., quantitative polymerase chain reaction, or qPCR for short).

Dr. Sherman Hom, Director of Regulatory Affairs at Medicinal Genomics

Plating systems have been used faithfully for close to 130 years in the food industry, and has performed reasonably well.2 But cannabis isn’t food and can’t be tested as if it were. In fact, plating methods have a host of major disadvantages that only show up when they’re used to detect cannabis pathogens. They are, in no particular order:

  1. A single plating system can’t enumerate a group of microorganisms and/or detect specific bacterial and fungal pathogens. This is further complicated by the fact that better than 98% of the microbes in the world do not form colonies.3 And there is no ONE UNIVERSAL bacterial or fungal SELECTIVE agar plate that will allow the growth of all bacteria or all fungal strains. For example, the 5 genus species of fungal strains implicated in powderly mildew DO NOT plate at all.
  2. Cannabinoids, which can represent 10-30% of a cannabis flower’s weight, have been shown to have antibacterial activity.4 Antibiotics inhibit the growth of bacteria and in some cases kill it altogether. Salmonella species & shiga toxin producing coli (STEC) bacteria, in particular, are very sensitive to antibiotics, which leads to either a false negative result or lower total counts on plates vs. qPCR methods.
  3. Plating methods cannot detect bacterial and fungal endophytes that live a part or all of their life cycle inside a cannabis plant.5,6 Examples of endophytes are the Aspergillus pathogens (A. flavus, A. fumigatus, A. niger, and A. terreus). Methods to break open the plant cells to access these endophytes to prepare them for plating methods also lyse these microbial cells, thereby killing endophytic cells in the process. That’s why these endophytes will never form colonies, which leads to either false negative results or lower total counts on plates vs. qPCR methods.
  4. Selective plating media for molds, such as Dichloran Rose-Bengal Chloramphenicol (DRBC) actually reduces mold growth—especially Aspergillus—by as much as 5-fold.This delivers false negative results for this dangerous human pathogen. In other words, although the DRBC medium is typically used to reduce bacteria; it comes at the cost of missing 5-fold more yeast and molds than Potato Dextrose Agar (PDA) + Chloramphenicol or molecular methods. These observations were derived from study results of the AOAC emergency response validation.7
  5. Finally, we’ve recently identified four bacterial species, which are human pathogens associated with cannabis that do not grow at the plating system incubation temperature typically used.8 They are Aeromonas hydrophila, Pantoea agglomerans, Yersinia enterocolitica, and Rahnella aquatilis. This lowers total counts on plates qPCR methods.

So why is plating still so popular? Better yet, why is it still the recommended method for many state regulators? Beats me. But I can hazard a couple of guesses.

A yeast and mold plate test

First, research on cannabis has been restricted for the better part of the last 70 years, and it’s impossible to construct a body of scientific knowledge by keeping everyone in the dark. Ten years ago, as one of the first government-employed scientists to study cannabis, I was tapped to start the first cannabis testing lab at the New Jersey Dept. of Health and we had to build it from ground zero. Nobody knew anything about cannabis then.

Second, because of a shortage of cannabis-trained experts, members of many regulatory bodies come from the food industry—where they’ve used plating almost exclusively. So, when it comes time to draft cannabis microbial testing regulations, plating is the default method. After all, it worked for them before and they’re comfortable with recommending it for their state’s cannabis regulations.

Finally, there’s a certain amount of discomfort in not being right. Going into this completely new area—remember, the legal cannabis industry didn’t even exist 10 years ago—we human beings like to have a little certainty to fall back on. The trouble is, falling back on what we did before stifles badly needed progress. This is a case where, if you’re comfortable with your old methods and you’re sure of your results, you’re probably wrong.

So let’s accept the fact that we’re all in this uncharted territory together. We don’t yet know everything about cannabis we need to know, but we do know some things, and we already have some pretty good tools, based on real science, that happen to work really well. Let’s use them to help light our way.

References

  1. J. Weissenbach. The rise of genomics. Comptes Rendu Biologies, 339 (7-8), 231-239 (2016).
  2. R. Koch. 1882. Die Aetiologie der Tuberculose.  Berliner Klinische Wochenschrift, 19, 221-230 (1882). 
  3. W. Wade. Unculturable bacteria—the uncharacterized organisms that cause oral infections. Journal of the Royal Society of Medicine, 95(2), 91-93 (2002).
  4. J.A. Karas, L.J.M. Wong, O.K.A. Paulin, A. C. Mazeh, M.H. Hussein, J. Li, and T. Vekov. Antibiotics, 9(7), 406 (2020).
  5. M. Taghinasab and S. Jabaji, Cannabis microbiome and the role of endophytes in modulating the production of secondary metabolites: an overview. Microorganisms 2020, 8, 355, 1-16 (2020).
  6. P. Kusari, S. Kusari, M. Spiteller and O. Kayser, Endophytic fungi harbored in Cannabis sativa L.: diversity and potential as biocontrol agents against host plant-specific phytopathogens. Fungal Diversity 60, 137–151 (2013).
  7. K. McKernan, Y. Helbert, L. Kane, N. Houde, L. Zhang, S. McLaughlin, Whole genome sequencing of colonies derived from cannabis flowers & the impact of media selection on benchmarking total yeast & mold detection tools,  https://f1000research.com/articles/10-624 (2021).
  8. K. McKernan, Y. Helbert, L. Kane, L. Zhang, N. Houde, A. Bennett, J. Silva, H. Ebling, and S. McLaughlin, Pathogenic Enterobacteriaceae require multiple culture temperatures for detection in Cannabis sativa L. OSF Preprints, https://osf.io/j3msk/, (2022)

Detecting Microbial Contamination in Cannabis

By Mike Clark
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Increasing cannabis use across the US has come with increased scrutiny of its health effects. Regulators and healthcare providers are not just concerned about the direct effects of inhaling or consuming cannabinoids, however, but also about another health risk: microbial contamination in cannabis products. Like any other crop, cannabis is susceptible to contamination by harmful pathogens at several points throughout the supply chain, from cultivation and harvesting to distribution. Many state regulators have set limits for microbial populations in cannabis products. Consequently, testing labs must adopt efficient screening protocols to help companies remain compliant and keep their customers safe.

Some of the pathogens common to cannabis flower include Aspergillus fungus species such as A. flavus, A. fumigatus, A. niger and A. terreus. Cannabis might also harbor harmful E. coli and Salmonella species, including Shiga toxin-producing E. coli (STEC). Regulations vary by state, but most have set specific thresholds for how many colony forming units (CFUs) of particular species can be present in a sellable product.

The gold standard method for detecting microbes is running cultures.

Growers and testing labs need to develop a streamlined approach to remain viable. Current methods, including running cultures on every sample, can be expensive and time-consuming, but by introducing a PCR-based screening step first, which identifies the presence of microbial DNA – and therefore the potential for contamination – laboratories can reduce the number of cultures they need to run, saving money and time.

The Risk of Aspergillus Contamination

Contamination from Aspergillus species can bring harm to cannabis growers and their customers. The state of Michigan is currently undergoing the largest cannabis recall in its history from Aspergillus contamination.

If contamination grows out of control, the pathogen can damage the cannabis plant itself and lead to financial losses. Aspergillus can also cause serious illness in consumers, especially those that are immunocompromised. If an immunocompromised person inhales Aspergillus, they can develop aspergillosis, a lung condition with a poor prognosis.

A Two-Step Screening Process

The gold standard method for detecting microbes is running cultures. This technique takes weeks to deliver results and can yield inaccurate CFU counts, making it difficult for growers to satisfy regulators and create a safe product in a timely manner. The use of polymerase chain reaction (PCR) can greatly shorten the time to results and increase sensitivity by determining whether the sample has target DNA.

Using PCR can be expensive, particularly to screen for multiple species at the same time, but a qPCR-based Aspergillus detection assay could lead to significant cost savings. Since the average presumptive positive rate for Aspergillus contamination is low (between 5-10%), this assay can be used to negatively screen large volumes of cannabis samples. It serves as an optional tool to further speciate only those samples that screened positive to comply with state regulations.

Conclusion

Overall, screening protocols have become a necessary part of cannabis production, and to reduce costs, testing labs must optimize methods to become as efficient as possible. With tools such as PCR technology and a method that allows for initial mass screening followed by speciation only when necessary, laboratories can release more samples faster with fewer unnecessary analyses and more success for cannabis producers in the marketplace.

Ask the Experts: Microbiological Contamination in Cannabis & What You Should Look for

By Cannabis Industry Journal Staff
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Testing cannabis and cannabis derived products for microbiological contamination should be a straightforward conversation for testing labs and producers. However, a patchwork of regulations and a wide variety of perspectives on what we should, or should not, be looking for has left much of the cannabis industry searching for reliable answers.

Organizations like the AOAC are taking the first crack at creating standardization in the field but there is still a long way to go. In this conversation, we would like to discuss the general requirements that almost all states share and where we see the industry headed as jurisdictions start to conform to the recommendations of national organizations like AOAC.

We sat down with Anna Klavins and Jessa Youngblood, two cannabis testing experts at Hardy Diagnostics, to get their thoughts on microbiology testing in the current state of the cannabis industry.

Q: What are the biggest challenges facing cannabis testing labs when it comes to microbiology?

The CompactDry Yeast and Mold Rapid plate provides fast results.

Anna Klavins & Jessa Youngblood: For microbiology testing, it comes down to a lack of standardization and approved methods for cannabis. In the US, cannabis regulation is written on a state-by-state level. As a result, the rules that govern every aspect of bringing these materials to market is as unique and varied as the jurisdiction writing them. When we are speaking specifically about microbiology, the question always comes back to yeast and mold testing. For some, the challenge will often be centered on the four main Aspergillus species of concern – A. terreus, A. niger, A. fumigatus, and A. flavus. For others, it will be the challenges of total count testing with yeast, mold, and bacteria. These issues become even more troublesome by the lack of recognized standard methodology. Typically, we expect the FDA, USP, or some other agency to provide the guidelines for industry – the rules that define what is safe for consumption. Without federal guidance, however, we are often in a situation where labs are required to figure out how to perform these tests on their own. This becomes a very real hurdle for many programs.

Q: Why is it important to use two different technologies to achieve confirmation?

Dichloran Rose Bengal Chloramphenicol (DRBC) Agar is recommended for the enumeration of yeasts and molds.

Klavins & Youngblood: The push for this approach was borne out of the discussions happening within the industry. Scientists and specialists from across disciplines started getting together and creating groups to start to hash out problems which had arisen due to a lack of standardization. In regards to cannabis testing, implementing a single method for obtaining microbiology results could be unreliable. When clients compared results across labs, the inconsistencies became even more problematic and began to erode trust in the industry. As groups discussed the best way to prove the efficacy of their testing protocol, it quickly became apparent that relying on a single testing method was going to be inadequate. When labs use two different technologies for microbiology testing, they are able to eliminate the likelihood of false positives or false negatives, whichever the case may be. In essence, the cannabis testing laboratories would be best off looking into algorithms of detecting organisms of interest. This is the type of laboratory testing modeled in other industries and these models are starting make their way into the cannabis testing space. This approach is common in many food and pharma applications and makes sense for the fledgling cannabis market as well.

About Anna Klavins

Anna Klavins earned a Molecular and Cellular Biology B.S. degree from Cal Poly San Luis Obispo while playing for the Cal Poly Division I NCAA women’s tennis team. Since joining Hardy Diagnostics in mid-2016, she has gained experience in FDA submissions [510(k)] for class II microbiology in vitro devices. She has worked on 15 projects which led to a microbiology device becoming FDA cleared. She has recently begun participating in the AOAC Performance Tested Methods program.

 

About Jessa Youngblood

Jessa Youngblood is the Food, Beverage and Cannabis Market Coordinator for Hardy Diagnostics. A specialist in the field of cannabis microbiology for regulatory compliance, she is seated with the AOAC CASP committee working on standard methods for microbiological testing in cannabis and hemp. She also sits on the NCIA Scientific Advisory Council as well as the ASTM Cannabis Council.

Content sponsored by Hardy Diagnostics.

3 Essential Components of Microbial Safety Testing

By Heather Ebling
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Microbial contamination on cannabis products represents one of the most significant threats to cannabis consumers, particularly immunocompromised patients who are at risk of developing harmful and potentially fatal infections.

As a result, regulatory bodies in the United States and Canada mandate testing cannabis products for certain microbes. The two most popular methods for microbial safety testing in the cannabis industry are culture-based testing and quantitative polymerase chain reaction (qPCR).

When considering patient safety, labs should choose a method that provides an accurate account of what is living on the sample and can specifically target the most harmful microbes, regardless of the matrix.

1. The Method’s Results Must Accurately Reflect the Microbial Population on the Sample

The main objective of any microbial safety test is to give the operator an indication of the microbial population present on the sample.

Figure 1: MA data collected directly from plant material before and after culture on 3M petrifilm and culture-based platforms.

Culture-based methods measure contamination by observing how many organisms grow in a given medium. However, not all microbial organisms grow at the same rate. In some cases, certain organisms will out-compete others and as a result, the population in a post-culture environment is radically different than what was on the original sample.

One study analyzed fifteen medicinal cannabis samples using two commercially available culture-based methods. To enumerate and differentiate bacteria and fungi present before and after growth on culture-based media, all samples were further subjected to next-generation sequencing (NGS) and metagenomic analyses (MA). Figure 1 illustrates MA data collected directly from plant material before and after culture on 3M petrifilm and culture-based platforms.

The results demonstrate substantial shifts in bacterial and fungal growth after culturing on the 3M petrifilm and culture-based platforms. Thus, the final composition of microbes after culturing is markedly different from the starting sample. Most concerning is the frequent identification of bacterial species in systems designed for the exclusive quantification of yeast and mold, as quantified by elevated total aerobic count (TAC) Cq values after culture in the total yeast and mold (TYM) medium. The presence of bacterial colonies on TYM growth plates or cartridges may falsely increase the rejection rate of cannabis samples for fungal contamination. These observations call into question the specificity claims of these platforms.

The Live Dead Problem

Figure 2: The enzyme is instantaneously inactivated when lysis buffer is added

One of the common objections to using qPCR for microbial safety testing is the fact that the method does not distinguish between live and dead DNA. PCR primers and probes will amplify any DNA in the sample that matches the target sequence, regardless of viability. Critics claim that this can lead to false positives because DNA from non-viable organisms can inflate results. This is often called the Live-Dead problem. However, scientists have developed multiple solutions to this problem. Most recently, Medicinal Genomics developed the Grim Reefer Free DNA Removal Kit, which eliminates free DNA contained in a sample by simply adding an enzyme and buffer and incubating for 10 minutes. The enzyme is instantaneously inactivated when lysis buffer is added, which prevents the Grim Reefer Enzyme from eliminating DNA when the viable cells are lysed (see Figure 2).

2. Method Must Be Able to Detect Specific Harmful Species 

Toxic Aspergillus spp., which is responsible for at least one confirmed death of a cannabis patient, grows poorly in culture mediums and is severely underreported by current culture-based platforms. And even when Aspergillus does grow in culture, there is a certain non-pathogenic Aspergillus species that look remarkably similar to their pathogenic cousins, making it difficult to speciate using visual identification alone.

Figure 3: The team spiked a known amount of live E. coli into three different environments

Conversely, qPCR assays, such as the PathoSEEK, are designed to target DNA sequences that are unique to pathogenic Aspergillus species, and they can be run using standard qPCR instruments such as the Agilent AriaMx. The primers are so specific that a single DNA base difference in the sequence can determine whether binding occurs. This specificity reduces the frequency of false positives in pathogen detection, a frequent problem with culture-based cannabis testing methods.

Additionally, Medicinal Genomics has developed a multiplex assay that can detect the four pathogenic species of Aspergillus (A. flavus, A. fumigatus, A. niger, and A. terreus) in a single reaction.

3. The Method Must Work on Multiple Matrices 

Figure 4: The team also placed TSB without any E. coli onto a petrifilm to serve as a control.

Marijuana infused products (MIPs) are a very diverse class of matrices that behave very differently than cannabis flowers. Gummy bears, chocolates, oils and tinctures all present different challenges to culture-based techniques as the sugars and carbohydrates can radically alter the carbon sources available for growth. To assess the impact of MIPs on colony-forming units per gram of sample (CFU/g) enumeration, The Medicinal Genomics team spiked a known amount of live E. coli into three different environments: tryptic soy broth (TSB), hemp oil and hard candy. The team then homogenized the samples, pipetted amounts from each onto 3M™ Petrifilm E. coli / Coliform Count (EC) Plates, and incubated for 96 hours. The team also placed TSB without any E. coli onto a petrifilm to serve as a control. Figures 3 and 4 show the results in 24-hour intervals.

Table 1: DNA was spiked into various MIPs

This implies the MIPs are interfering with the reporter assay on the films or that the MIPs are antiseptic in nature.

Many MIPs use citric acid as a flavoring ingredient which may interfere with 3M reporter chemistry. In contrast, the qPCR signal from the Agilent AriaMx was constant, implying there is microbial contamination present on the films, but the colony formation or reporting is inhibited.

Table 3: SenSATIVAx DNA extraction can successfully lyse the cells of the microbes
Table 2: Different numbers of DNA copies spiked into chocolate

This is not an issue with DNA-based methods, so long as the DNA extraction method has been validated on these matrices. For example, the SenSATIVAx DNA extraction method is efficient in different matrices, DNA was spiked into various MIPs as shown in Table 1, and at different numbers of DNA copies into chocolate (Table 2). The SenSATIVAx DNA extraction kit successfully captures the varying levels of DNA, and the PathoSEEK detection assay can successfully detect that range of DNA. Table 3 demonstrates that SenSATIVAx DNA extraction can successfully lyse the cells of the microbes that may be present on cannabis for a variety of organisms spiked onto cannabis flower samples.

Swetha Kaul, PhD

Colorado vs. California: Two Different Approaches to Mold Testing in Cannabis

By Swetha Kaul, PhD
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Swetha Kaul, PhD

Across the country, there is a patchwork of regulatory requirements that vary from state to state. Regulations focus on limiting microbial impurities (such as mold) present in cannabis in order for consumers to receive a safe product. When cultivators in Colorado and Nevada submit their cannabis product to laboratories for testing, they are striving to meet total yeast and mold count (TYMC) requirements.In a nascent industry, it is prudent for state regulators to reference specific testing methodologies so that an industry standard can be established.

TYMC refers to the number of colony forming units present per gram (CFU/g) of cannabis material tested. CFU is a method of quantifying and reporting the amount of live yeast or mold present in the cannabis material being tested. This number is determined by plating the sample, which involves spreading the sample evenly in a container like a petri dish, followed by an incubation period, which provides the ideal conditions for yeast and mold to grow and multiply. If the yeast and mold cells are efficiently distributed on a plate, it is assumed that each live cell will give rise to a single colony. Each colony produces a visible spot on the plate and this represents a single CFU. Counting the numbers of CFU gives an accurate estimate on the number of viable cells in the sample.

The plate count methodology for TYMC is standardized and widely accepted in a variety of industries including the food, cosmetic and pharmaceutical industries. The FDA has published guidelines that specify limits on total yeast and mold counts ranging from 10 to 100,000 CFU/g. In cannabis testing, a TYMC count of 10,000 is commonly used. TYMC is also approved by the AOAC for testing a variety of products, such as food and cosmetics, for yeast and mold. It is a fairly easy technique to perform requiring minimal training, and the overall cost tends to be relatively low. It can be utilized to differentiate between dead and live cells, since only viable living cells produce colonies.

Petri dish containing the fungus Aspergillus flavus
Petri dish containing the fungus Aspergillus flavus.
Photo courtesy of USDA ARS & Peggy Greb.

There is a 24 to 48-hour incubation period associated with TYMC and this impedes speed of testing. Depending on the microbial levels in a sample, additional dilution of a cannabis sample being tested may be required in order to count the cells accurately. TYMC is not species-specific, allowing this method to cover a broad range of yeast and molds, including those that are not considered harmful. Studies conducted on cannabis products have identified several harmful species of yeast and mold, including Cryptococcus, Mucor, Aspergillus, Penicillium and Botrytis Cinerea. Non-pathogenic molds have also been shown to be a source of allergic hypersensitivity reactions. The ability of TYMC to detect only viable living cells from such a broad range of yeast and mold species may be considered an advantage in the newly emerging cannabis industry.

After California voted to legalize recreational marijuana, state regulatory agencies began exploring different cannabis testing methods to implement in order to ensure clean cannabis for the large influx of consumers.

Unlike Colorado, California is considering a different route and the recently released emergency regulations require testing for specific species of Aspergillus mold (A. fumigatus, A. flavus, A. niger and A. terreus). While Aspergillus can also be cultured and plated, it is difficult to differentiate morphological characteristics of each species on a plate and the risk of misidentification is high. Therefore, positive identification would require the use of DNA-based methods such as polymerase chain reaction testing, also known as PCR. PCR is a molecular biology technique that can detect species-specific strains of mold that are considered harmful through the amplification and analysis of DNA sequences present in cannabis. The standard PCR testing method can be divided into four steps:

  1. The double stranded DNA in the cannabis sample is denatured by heat. This refers to splitting the double strand into single strands.
  2. Primers, which are short single-stranded DNA sequences, are added to align with the corresponding section of the DNA. These primers can be directly or indirectly labeled with fluorescence.
  3. DNA polymerase is introduced to extend the sequence, which results in two copies of the original double stranded DNA. DNA polymerases are enzymes that create DNA molecules by assembling nucleotides, the building blocks of DNA.
  4. Once the double stranded DNA is created, the intensity of the resulting fluorescence signal can uncover the presence of specific species of harmful Aspergillus mold, such as fumigatus.

These steps can be repeated several times to amplify a very small amount of DNA in a sample. The primers will only bind to the corresponding sequence of DNA that matches that primer and this allows PCR to be very specific.

PCR testing is used in a wide variety of applications
PCR testing is used in a wide variety of applications
Photo courtesy of USDA ARS & Peggy Greb.

PCR is a very sensitive and selective method with many applications. However, the instrumentation utilized can be very expensive, which would increase the overall cost of a compliance test. The high sensitivity of the method for the target DNA means that there are possibilities for a false positive. This has implications in the cannabis industry where samples that test positive for yeast and mold may need to go through a remediation process to kill the microbial impurities. These remediated samples may still fail a PCR-based microbial test due to the presence of the DNA. Another issue with the high selectivity of this method is that other species of potentially harmful yeast and mold would not even be detected. PCR is a technique that requires skill and training to perform and this, in turn, adds to the high overall cost of the test.

Both TYMC and PCR have associated advantages and disadvantages and it is important to take into account the cost, speed, selectivity, and sensitivity of each method. The differences between the two methodologies would lead to a large disparity in testing standards amongst labs in different states. In a nascent industry, it is prudent for state regulators to reference specific testing methodologies so that an industry standard can be established.

Swetha Kaul, PhD

An Insider’s View: How Labs Conduct Cannabis Mold Testing

By Swetha Kaul, PhD
2 Comments
Swetha Kaul, PhD

As both recreational and medical cannabis legalization continues to progress across the country, each state is tasked with developing regulatory requirements to ensure that customers and patients receive clean cannabis for consumption. This requires cannabis to undergo laboratory testing that analyzes the presence of microbial impurities including yeast and mold.

Some states, such as Colorado, Nevada, Maine, Illinois and Massachusetts use total yeast and mold count testing (TYMC) and set a maximum yeast and mold count threshold that cultivators must fall below. Other states, such as California, require the detection of species-specific strains of Aspergillus mold (A. fumigatus, A. flavus, A. niger and A. terreus), which requires analyzing the DNA of a cannabis sample through polymerase chain reaction testing, also known as PCR.

Differences in state regulations can lead to different microbiological techniques implemented for testing.Before diving in further, it is important to understand the scientific approach. Laboratory testing requirements for cannabis can be separated into two categories: analytical chemistry methods and microbiological methods.

Analytical chemistry is the science of qualitatively and quantitatively determining the chemical components of a substance, and usually consists of some kind of separation followed by detection. Analytical methods are used to uncover the potency of cannabis, analyze the terpene profile and to detect the presence of pesticides, chemical residues, residuals solvents, heavy metals and mycotoxins. Analytical testing methods are performed first before proceeding to microbiological methods.

Petri dish containing the fungus Aspergillus flavus
Petri dish containing the fungus Aspergillus flavus. It produces carcinogenic aflatoxins, which can contaminate certain foods and cause aspergillosis, an invasive fungal disease.
Photo courtesy of USDA ARS & Peggy Greb.

Microbiological methods dive deeper into cannabis at a cellular level to uncover microbial impurities such as yeast, mold and bacteria. The techniques utilized in microbiological methods are very different from traditional analytical chemistry methods in both the way they are performed and target of the analysis. Differences in state regulations can lead to different microbiological techniques implemented for testing. There are a variety of cell and molecular biology techniques that can be used for detecting microbial impurities, but most can be separated into two categories:

  1. Methods to determine total microbial cell numbers, which typically utilizes cell culture, which involves growing cells in favorable conditions and plating, spreading the sample evenly in a container like a petri dish. The total yeast and mold count (TYMC) test follows this method.
  2. Molecular methods intended to detect specific species of mold, such as harmful aspergillus mold strains, which typically involves testing for the presence of unique DNA sequences such as Polymerase Chain Reaction (PCR).


Among states that have legalized some form of cannabis use and put forth regulations, there appears to be a broad consensus that the laboratories should test for potency (cannabinoids concentration), pesticides (or chemical residues) and residual solvents at a minimum. On the other hand, microbial testing requirements, particularly for mold, appear to vary greatly from state to state. Oregon requires random testing for mold and mildew without any details on test type. In Colorado, Nevada, Maine, Illinois and Massachusetts, regulations explicitly state the use of TYMC for the detection of mold. In California, the recently released emergency regulations require testing for specific species of Aspergillus mold (A. fumigatus, A. flavus, A. niger and A. terreus), which are difficult to differentiate on a plate and would require a DNA-based approach. Since there are differences in costs associated and data produced by these methods, this issue will impact product costs for cultivators, which will affect cannabis prices for consumers.