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Why is Microbial Cannabis Testing So Important?


As medical and recreational cannabis is spreading quickly across the U.S., so is knowledge of the various contaminants hiding in the plant. Many people are now aware of the problems with pesticides, but few understand the hidden dangers of microbes—Or microscopic organisms that you can’t see with the naked eye.

Breaking Down the Different Microbes Found in Cannabis

Microbes are difficult to detect because they’re so small and with cannabis, it’s harder because the flowers are covered in resin glands that produce copious amounts of sticky cannabinoids, terpenes, and flavonoids that become crystal-like when they dry. Microbes can get inside the flowers and show no visible signs of disease.

Microbiological contamination comes from water, nutrient sources, the air, and human factors such as poor hygiene from the plants’ caretakers during cultivation, harvesting, and product processing.

Bacteria – These are single-celled organisms that contain DNA. A teaspoon of nutrient-rich soil can hold between 100 million and 1 billion bacteria.

Archaea – These prokaryotic organisms grow in different soil conditions that until recently, were thought to be a form of bacteria. Similar to a bacterium, they are present everywhere including in the human digestive system.

Fungi – There are close to 144,000 known species in the Fungi Kingdom. Examples of fungus include multiple molds, yeasts, smuts, mildews, rusts, and of course, mushrooms.

Protists – The unicellular organisms are members of the eukaryotic group and the Protista kingdom that don’t fit into other microbe classifications. They aren’t bacteria, archaea, or fungus. There are about 60,000 species of protists.

Viruses – These organisms can infect plants, animals, fungi, people, and even bacteria. Unlike the other microbes, these are very complex and are considered parasitic. Scientists don’t know how many viruses there are in the world, but, given how many are in a person’s body at once when they have the flu (100 trillion), it’s easy to see that number is astronomical.

Many of these are found in cannabis flowers. Steep Hill Laboratories sampled 20 samples from Northern California Dispensaries a few years ago. The results included 4,000 total fungal taxonomic classifications, and the 20-most present were Aspergillus, Cryptococcus, and Mucor.

Are All Microbes Dangerous?

Like many things in life, there are good and bad microbes. Your plants need some microbes to grow. The microbiome is complicated, and the science community is still learning about the benefits of different aspects that can improve growth and reduce contaminations.

Some Bacteria and fungi (mold) can break down the nutrients in the soil to benefit plant growth by making them easier to absorb.

In terms of the human body and health, Dr. Martin J. Blaser at the New York University School of Medicine explains, “The current estimate is that humans have 10 trillion human cells and about 100 trillion bacterial cells.”

Yes—Many dangerous microbes can make you sick, but more exist to help with plant growth and human health.

According to the September 2013, Scientific American Article, “Microbes Help Grow Better Crops,” a pilot study in Virginia found that spraying a local bacteria from the West Coast on tomato seedlings resulted in an ant-salmonella effect on the crop.

Microbes can be dangerous and even deadly for medical cannabis patients with a weakened immune system from disease, or radiation, and chemotherapy treatment. These people are often prescribed antiviral, antifungal, and antibacterial medicines to prevent their risk of developing infections.

In most cases, their medical team even asks them to avoid certain foods and materials because of the naturally occurring Aspergillus molds and bacteria, such as,

  • Berries
  • Fresh Salsa
  • Leafy greens
  • Planting Soils
  • Fresh-cut Flowers

Microbial Testing Guidelines Don't Exist

It’s unfortunate, but, like pesticide testing, there aren’t any federal guidelines for microbial cannabis testing, leaving the rules up to each state. The Association of Official Analytical Chemists (AOAC) publishes standards for microbiological and chemical standards around the globe does not offer a guide or laboratory certification for microbial cannabis testing.

Many labs, such as Earth Labs, follow the American Herbal Products Association (AHPA) guidelines for the allowable amount of living microbes in each sample. A common reason these organizations won’t issue guiding principles for cannabis is because of how many methods are available to consume the plant.

For example, people eat tomatoes raw and cook them, but they don’t smoke, vaporize, or extract the 400 or more compounds in the fruit with alcohol and absorb it under their tongue.

Other associations have general guidelines for herbal products. However, none of them offer microbial level recommendations specific to cannabis for the same reasons.

The AHPA guidelines include the various levels and requirements of these organizations in their published instructions mentioned above.

  • European Herbal Infusions Association (EHIA)
  • European Pharmacopoeia (EP)
  • International Standard/American National Standard for Dietary Supplements
  • United States Pharmacopoeia Convention
  • World Health Organization (WHO)

Labs measure microbes by colony-forming units or CFU. At least two states, Colorado and Washington, also follow the AHPA guidelines.

Step-By-Step Microbial Testing

The test for microbes isn’t the same as others that screen for insecticides, heavy metals, and non-biological contaminants.

These screenings apply to fresh and dry flowers because microbes are rarely found in concentrates. Biological contaminants at this stage are most often the result of improper handwashing by the staff handling the samples.

  1. Prepare the sample
  2. Place the sample on an AGAR plate, which is a petri dish with a mix of chemicals and nutrients that allow bacteria and yeast to grow from.
  3. Incubate the sample at the same, warm temperature for a few days
  4. Count how many colonies grew during incubation to determine the colony-forming units (CFU).

The final number will decide if your sample is safe and meets the allowable limits set forth by the AHPA. The decarboxylation process or heating the dry flowers may not thoroughly sterilize fungi and bacteria.

All products that don’t meet these standards should be destroyed.

What are Allowable Limits?

Yes—There are allowable amounts of microbes in dry, unprocessed cannabis. These limits outline the difficulties cultivators can have removing all microbes and corresponds with the knowledge that there are necessary and safe microorganisms.

Molds are ubiquitous, and small amounts are found in almost every sample. However, exposure to high levels of microorganisms such as molds and bacteria are known to cause health problems and can be particularly dangerous to patients that have existing medical conditions.

Two microbes aren’t allowed, even in trace amounts in California and Colorado.

  • Escherichia coli (E. Coli)
  • Salmonella

Oregon allows E. Coli levels unders 100 CFU/g.

The total aerobic microbial count in each sample is 107. Microbes that are within limits, include:

  • Combined yeast and mold - 105
  • Enterobacteria (Bile-tolerant gram-negative bacteria) - 104

The Oregon Health Authority notes in their guidelines that people with compromised immune systems shouldn’t smoke or vape cannabis to avoid potential respiratory infections from a few species of Aspergillus mold.

Most states and labs set very low limits, which significantly reduces the chances of these molds, bacteria, and viruses from showing up on the shelves of your local dispensary.

How Do I Know if My Cannabis Has Contaminants?

If you purchase cannabis, only go through a licensed and regulated dispensary. It would be best to direct your questions about products to a qualified staff member. They should be able to advise you about where the flowers are grown and provide copies of lab reports that show the product’s acceptable levels.

Most state cannabis programs have some regulations in place for testing products sold legally. Home cultivators aren’t out of options—you can purchase kits to test your flowers or take a sample to a nearby lab. Both choices require additional out-of-pocket costs. With an independent lab, your sample can also be tested for other contaminants and potency.

Don’t try to mail samples. It’s not legal to send cannabis through the U.S. postal system, or companies like FedEx.

There is a silver lining if this information disconcerts you—Cannabis has natural antimicrobial properties. If something slips through testing, these medicinal benefits of this plant have a backup plan with the potential to protect you from the contaminants.

Microbial cannabis testing is increasing in states with legal recreational and medical use. However, with no official guidelines, there will continue to be some confusion and differences in testing requirements from state-to-state until the U.S. government legalizes cannabis on the federal level.

Legalization would allow agencies, such as the U.S. Food and Drug Administration (FDA), the Department of Health and Human Services (HHS), the Environmental Protection Agency (EPA), and the U.S. Department of Agriculture (USDA) to study and work together developing safe consumption guidelines for medical and recreational use.