This review article, written from the point of view of an experienced pharmaceutical microbiologist, discusses the risks of microbial contamination for the full range of cannabis-derived products and recommends the most appropriate microbiological quality requirements for each of these products by benchmarking against the microbiological quality recommendations from the American Herbal Products Association (AHPA), the World Health Organization (WHO), European Pharmacopeia (Ph. Eur.), and the U.S. Pharmacopeia (USP) for powdered cannabis, dietary supplements, herbs, botanical products, and nonsterile drug products.
With a rapidly emerging state-regulated industry producing both recreational and medicinal cannabis products, there are many questions surrounding the microbiological attributes of cannabis-derived products. This review article discusses the risk of microbial contamination of these products and the most appropriate microbiological specifications and test methods for the widely different products that range from smoked powdered cannabis buds to chemically defined pharmaceutical drug products. Part of the challenge is that cannabis-derived products based on the consumer (medical and recreational) and mode of use may be viewed as herbal products, recreational drugs, foods, or pharmaceutical drug products. Critical issues to be addressed by state regulators and the cannabis industry alike are the microbiological specifications and test methods for these widely different products.
What are the biggest risks with cannabis-derived products? In medical use, smoking cannabis has been used to control weight loss associated with the human immunodeficiency virus (HIV) and acquired immune deficiency syndrome (AIDS), preventing nausea associated with chemotherapy, and alleviating pain associated with a range of illnesses. These patient populations will be more susceptible to microbial infection than recreational users. With respect to mode of administration, the microbiological quality requirement will be widely different for cannabis that is smoked, vaped, topically applied, or eaten. As many medicinal cannabis users have severely compromised immune systems, medical cannabis distributed by licensed producers in the Netherlands and Canada is irradiated for control of the bioburden but not to sterilize the product.
Does the scientific literature report concerns with the microbial contamination of cannabis? This issue was addressed by the author in an earlier publication that may have escaped the cannabis industry’s attention because of its publication in a pharmaceutical trade journal (1). Groups prone to chronic pulmonary aspergillosis (CPA) associated with medical or recreational use of cannabis (2–12) include immune-compromised individuals receiving chemotherapy and corticosteroids; solid organs and stem cell transplant recipients; and HIV or AIDS patients. In addition to CPA that has a high mortality rate, if not treated early, chronic use of smoked cannabis is associated with allergic broncho-pulmonary aspergillus (ABPA) (13). An authoritative review on the Aspergillus and Aspergillosis website (14) stated that the overall risk of aspergillosis appeared low, given the large number of cannabis smokers. An exception noted would be invasive aspergillosis in highly immune-compromised patients. This suggests that medical cannabis that is smoked should have more stringent fungal specifications than other products.
In addition, cannabis may be contaminated with other human pathogens during its cultivation, processing, and distribution. Outbreaks of hepatitis B (15) hepatitis A (16), and salmonellosis (17) have been reported. The author expects that this type of contamination may be more likely in field-grown cannabis plants using irrigation water, and poor hygiene practices among harvesters and processors, than greater capitalized greenhouse-grown cannabis operations.
Published surveys of the microbial populations of powdered cannabis in peer-reviewed journals are few and of varying technical rigor. Higher mold numbers using the selective Sabouraud Dextrose Agar (SDA) for cannabis compared to tobacco (200 to 300 versus 104 to 107 CFU/g), with the predominant fungi Penicillium spp., Aspergillus fumigatus, and A. flavus have been reported (18).
This study reported that cigarette smoke was negative for mold but cigarettes are tightly rolled and burn at higher temperatures than joints. Other studies have shown that smoke from both burning tobacco and marijuana cigarettes contain fungal spores (19,20). In an evaluation of the quality of medicinal-grade and coffee shop-purchased cannabis in the Netherlands (21), it was reported that irradiated medicinal-grade cannabis contained less than 10 CFU/g enterobacteria and Gram-negative bacteria (bile-tolerant, Gram-negative bacterial count) and less than 100 CFU/g molds and aerobic bacteria (total aerobic microbial count) while 10 samples of coffee shop cannabis ranged from less than 10 to 80,000 CFU/g bile-tolerant, Gram-negative bacterial counts and 120 to 480,000 CFU/g total aerobic microbial counts.
The contaminants from one of the 10 samples were identified as the fecal bacterium E. coli and molds of the common genera Penicillium, Cladosporium, and Aspergillus.
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Tony Cundell is a New York-based consulting microbiologist serving the pharmaceutical industry. Direct correspondence to: [email protected]
How to Cite This Article
T. Cundell, Cannabis Science and Technology 2(4), 36–49 (2019).