Microbiological testing for Cannabis plant material and finished products
Cannabis can be grown in several different environments (both indoors and outdoors), processed in many different ways and utilized or ingested by multiple routes. Each of these pathways come with their own set of microbiological risks.
Living cannabis plants do not support high levels of bacterial growth, but fungal growth is fairly common. Mold is perhaps the single most important quality issue in Cannabis production. Outdoor plants are exposed to a wide variety of fungal species. Indoor plants are exposed to less of these and can potentially be kept cleaner. In practice, however, many indoor plants are exposed to inappropriate watering, humidity, fertilizer or ventilation conditions. All of these can contribute to very high levels of mold.
Even under ideal conditions, it is possible that small numbers of cells or spores, capable of causing human disease, may be present on plant material from contact with air, soil or water. If any of these species are capable of replicating aggressively, either on dried plant material or upon contact with humans, they could theoretically prove to be a threat.
Once the plants are harvested, they are trimmed, dried and cured. These processes present significant opportunities for contamination. Harvesting and trimming are the stages at which there is the greatest level of human handling. Human pathogens can easily be transferred to the flower material at this stage. If moisture levels are too high during this period, both mold and bacterial levels will rise above acceptable levels.
Once cured, flower material can be smoked or inhaled by vaporization, but it is also frequently used to make extracts or concentrates that can themselves be smoked or vaporized, or added to products intended for oral ingestion. These steps often utilize high temperature (~ 120°C for 30 min). This decarboxylation step is essentially a heat-kill step, and unlikely to allow microbes to survive.
The same decarboxylation process happens during smoking. In either case the temperature required is high enough to kill growing bacteria and fungi but not high enough to kill spores.
The microbial tests required for Cannabis products include the following:
- Total aerobic bacteria count (TAC): A very common indicator test, provides a general sense of the cleanliness of production or processing.
- Total Yeast and Mold count (TYM): Since mold is the most common type of microbial growth on Cannabis, the Total Yeast and Mold test is a general quality indicator.
- Bile–resistant gram-negative bacteria: The purpose of this test is to define a group of bacteria that would include the majority of gut-borne pathogens.
- Escherichia coli count: The purpose of this test is the indication of fecal contamination during the production of cannabis from humans or from contaminated soil or water. It could indicate a possible presence of enteric pathogens, and it is likely to reflect a problem in the production process.
- Salmonella count: Salmonella is not uncommon in the environment, and can be found as a contaminant of both soil and water. It is a potentially quite dangerous pathogen, it could be found on cannabis and it would survive the curing process and the heat-kill step and could cause an outbreak.
- Pseudomonas aeruginosa count: Pseudomonas is a large genus of gram-negative bacteria. P. aeruginosa is the human pathogen in the genus, and it is found in water, soil, on many plants and it can colonize on many different types of surface.P. aeruginosa is potentially dangerous.
- Staphylococcus aureus count: S. aureus is a gram-positive bacterium, member of the normal flora of the human body, frequently found in the nose, respiratory tract, on the skin and in the gut mucosa.