Testing Cannabis for Bile-Tolerant Gram-negative Bacteria

Bile-tolerant gram negative bacteria are defined as bacteria that grow on violet red bile glucose agar (VRBGA) medium. That is gram negative bacteria that grow in the presence of bile salts, are non-lactose fermenting but able to utilize glucose. Some bile-tolerant gram negative bacteria include members of the family Enterobacteriaceae (including Klebsiella spp., E. coli), Pseudomonads and Aeromonas It is is a large group of bacteria with more than 200 species. While most members of the bile-tolerant gram-negative bacteria are not pathogenic to humans, they can cause food-borne illness as well as food spoilage. As a result, food manufacturers used to test products for bile-tolerant gram-negative bacteria to ensure quality and long shelf life.

Why test Cannabis for Bile-tolerant gram-Negative Bacteria

At present, bile-tolerant gram negative bacteria test is considered outdated by some microbiologists since there are other better tests that can serve the same purpose. The test was in use many decades ago and is no longer used in food-safety testing. The purpose of this test was to define a group of bacteria that would include the majority of gut-borne pathogens. Several other indicator categories have since gained favor for the purpose of showing the potential for fecal contamination. Although the test is considered outdated many Cannabis regulators require cannabis samples pass bile-tolerant gram-negative bacteria testing before it can be sold to the public.

Health Canada states that:

For products containing live microorganisms, a method of enumerating viable members of the family, Enterobacteriaceae should be used, e.g., USP <2021> “Enterobacterial count (Bile tolerant gram negative bacteria)” or the Health Canada test MFLP-43 “Determination of Enterobacteriaceae”. Note that selective testing for coliforms or only for members of the genus Enterobacter (i.e. a subset of the family Enterobacteriaceae) is not considered sufficient as it may potentially fail to screen for other gram negative facultative rods that belong to the same family of Enterobacteriaceae and are also known pathogens such as members of the genera Klebesiella, Shigella, etc.