External Quality Assessment of Laboratories Performing Microbiology Testing of Cannabis – A Pilot Study

The exercise was conducted in January 2023 by Proficiency Testing Canada (PTC) and Canadian Microbiology Proficiency Testing (CMPT). The main goals of the round were to assess laboratories’ abilities to competently perform the prescribed analyses and to identify any problems with the Scheme design.

This pilot proficiency testing (PT) survey consisted of three independent schemes:

  • Microbiology in Cannabis Candy Surrogate: consisted of three candy samples containing Escherichia coli, Enterobacter species, or no bacteria.
  • Microbiology in Cannabis Surrogate: consisted of two cannabis vegetation samples, containing E. coli or no bacteria.
  • Microbiology in Oil: consisting of two oil samples, each containing E. coli or no bacteria.

A hop flower being held in tweezers.Participants were asked to use the method commonly used in their laboratory. Candy and vegetation samples were suitable for qualitative (presence / absence) and quantitative analysis; oil samples were suitable for presence/absence determination only.


A total of 16 laboratories volunteer to participate in this Pilot project representing 6 provinces in Canada. Approximately 50% of the laboratories performed quantitative analysis as well as presence/absence.


Candy surrogate:

Laboratories were asked to report the presence/absence of E. coli, Enterobacter species, or total coliforms in each sample.


Vegetation and Oil:

Laboratories were asked to report the presence/absence of E. coli in each sample.



In general, participants’ performance was good. The exception to this was the large number of participants (7) who reported the presence of Enterobacter sp. in a Candy sample although this sample was only spiked with E. coli. The high incidence of false positives for Enterobacter sp. was probably due to the use of non-selective media that does not distinguish between E. coli and other non-E. coli coliforms.


All Participants were encouraged to investigate their performance as compared to that of other participants and methods.

Proficiency testing participation for Cannabis testing laboratories is not yet mandatory in Canada, however, testing laboratories wanting to have confidence in their own testing performance, and to reassure their customers of their testing quality, should consider enrolling in an external quality assessment program such as a Cannabis Proficiency Testing program.

This participation, as discussed in an article in this newsletter allows peer group comparisons of test results within a particular method and between different analytical methods; this is of particular importance within a new testing industry as Microbiology Cannabis testing.

For more information about our Cannabis Microbiology Proficiency Testing please contact CMPT.

Posted in Article, Industry Microbiology