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Thousands of Types of Fungi, Bacteria Found in Californian Cannabis

By Leo Bear-McGuinness
Published: Jul 25, 2018   
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Patients undergoing treatments such as chemotherapy or stem cell transfers may seek out medicinal cannabis for pain relief. However, according to ongoing research by at team at the University of California, these individuals may be placing themselves at a high risk of bacterial and fungal infections. Considering the weakened states of the patients’ immune systems and the rising prescriptions of medicinal cannabis in countries such as the USA, the findings of this research are especially pertinent.

Moreover, the group state that it would be unlikely that any recovery of bacterial and fungal pathogens in a patient would trigger a search for unusual exposures. For example, the presence of Gram-negative bacilli could be put down to healthcare-associated pneumonia. Thus, the researchers strongly advise such patients against the use of vaporized or inhaled cannabis and advocate for further research. 

Why cannabis patients may be at risk

Following certain treatments, highly immunocompromised patients, such as those receiving chemotherapy, may smoke or vaporize cannabis products in an attempt to relieve their pain and nausea or stimulate their appetite. Depending on the US state or country, this practice may be sanctioned by a medical practitioner. 

Irrespective of this, it is common throughout many countries for such patients to be prescribed antibacterial, antifungal, and antiviral agents to stave off the risk of infection. Many doctors and health practitioners will even advise their patients to avoid natural materials and products, such as soils, plants, cut flowers, fresh salsa, and berries, due to the natural presence of Aspergillus molds and bacteria. However, these recommendations do not cover the potential infectious risks of cannabis, which – as the researchers suggest – may harbor similar pathogens as those found in vetoed plant materials.

Testing for microbial contamination

Using both metagenomics approaches and 16S/internal transcribed spacer community analysis the researchers aimed to better understand the potential microbial contaminants patients may expose themselves to.   

Twenty cannabis samples from different northern Californian dispensaries were collected by Steep Hill Laboratories, cataloged and, processed using a PowerSoil DNA Isolation Kit. The fungal communities were assessed by internal transcribed spacer gene sequence analysis and the bacterial communities were analyzed using published methods. To distinguish between the different species, present in the microbiome more specific whole metagenome analyses were used. 

On the fungal side, the analyses resulted in around 4000 total fungal taxonomic classifications; many of the top 20 genera present contained opportunistic pathogens (Cryptococcus, Mucor, Aspergillus). On the bacterial side, analyses of one sample resulted in around 5000 operational taxonomic units, and specific metagenome analyses showed that many of the pathogens present are those traditionally associated with hospital-acquired infections (E. coli, K. pneumoniae, P. aeruginosa).

The level of risk

While the university’s initial research was limited to genomic analyses, which only highlighted the numbers of pathogens present and not a patient’s actual risk of infection, subsequent research by the team has involved testing the antibiotic resistance of the detected pathogens.

In this recent study, 25% of P. aeruginosa isolates showed high-level resistance to imipenem (>8 μg/mL) and aztreonam (>32 μg/mL) and one isolate even exhibited resistance to ciprofloxacin (>4 μg/mL) and levofloxacin (>8 μg/mL). In addition, up to 80% of Enterobacter cloacae isolates were resistant to ampicillin (>32 μg/mL), ampicillin-sulbactam (>32/ 16 μg/mL), and cefazolin (>32 μg/mL). In total 12% of all tested samples harbored resistance to at least one commonly prescribed antibacterial agent. 

To further demonstrate the risk of infection these pathogens pose, the researchers also highlight previous studies which have proven that multiple fungi and bacteria can be cultured from cannabis products, confirming that viable organisms can be recovered from the plant material. Furthermore, the group point to previous studies which have shown that viable organisms can be successfully cultured from smoke even after water filtration. Thus, the temperature of smoked cannabis samples (50°-60°C) may not sterilize pathogens and instead potentially provide an effective method of entry into the terminal bronchioles and alveoli. 

Ultimately, there is still little evidence to prove that the pathogens present in cannabis samples have directly led to infections in immunocompromised patients. Still, the results presented by the University of California researchers do demonstrate the significant potential for cannabis-transferred infections, and so – as the researchers themselves recommend –further research is needed to clarify the risks.

Looking to future research

The team’s results suggest that any interaction with cannabis products may expose an immunocompromised patient to a number of bacterial and fungal pathogens. Moreover, the recovery of these organisms in a patient with a weakened immune system would be unlikely to initiate a search for unusual exposures. 

Thus, the team strongly recommends further research into the susceptibility profiles of these organisms and their risk to patients. Such findings could one day allow medical practitioners to more accurately predict the microbial risks posed by the medical marijuana they prescribe to their patients. But, until the results of this future research are obtained, the team strongly advise immunocompromised patients against the use of vaporized or inhaled marijuana, for their own safety. 


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