Total Yeast and Mold Count Assay Method Validation

We have modeled our method validation for the yeast and mold assay after the AOAC SMPR for Aspergillus and we have participated with the AOAC's Emergency Response Validation (ERV) for TYM.

Updated April 2021

As of April, 2021, the AOAC Emergency Response Validation (ERV) for Total Yeast and Mold study is still ongoing and no certifications have been issued by the AOAC. There are several method developers involved in the study that are submitting their methods to the AOAC. Medicinal Genomics TYM Assay has been submitted and all inclusion/exclusion validation data is complete as well as all internal and third party matrix study data. 

We will publish our internal validation work and launch a new protocol for TYM that incorporates a new version of our PathoSEEK® Master Kit.

Please see AOAC's page for more detail:

There has been a lot of misinformation and confusion in the field with regards to qPCR and enumeration for TYM on cannabis. There has been equally as much confusion and misinformation about what techniques are actually certified by any agency or governing body for cannabis testing.

Continuous Process Improvement

In 2019, the AOAC developed a Standard Method Performance Requirements (SMPR) for Aspergillus, E.coli, and Salmonella detection on cannabis. These are three separate SMPRs. There is a draft SMPR for STEC E.Coli. A draft SMPR for Total Yeast and Mold was just released in early 2021 and is in open comment period.

Our original validation of Total Yeast and Mold Count was completed in 2015 when we launched the assay. The data in our newest validation document reflects our more current validation efforts performed in our lab in 2020 as well as in independent third party labs.

Continuous process improvement is in our DNA, and we will always be transparent about our validation work and forward thinking with our product development.

Total Yeast and Mold Count Assay Design

The PathoSEEK® Total Yeast and Mold Count Detection Assay is used to detect species classified as yeasts and molds. The results of a Total Yeast and Mold Count (TYM) test are an indication of yeast and mold contamination on a cannabis sample. The Assay targets these species using the FAM fluorophore. 

The primer design targets the 16S Internal Transcribed Spacer (ITS) region that is common to yeasts and molds. Our inclusion results are described in our validation document.

Regulations for total count microbial threshold tests currently use nomenclature from culture-based methods to set acceptable thresholds. It is necessary to convert the quantification cycle (Cq) value from the qPCR assay to colony forming units (CFU). 

As noted in our validation document, Botrytis cinerea was not detected but as mentioned above this does not form colonies in 48 hours and will create discordance with CFU/g correlations. As a result, we have made an independent assay for both Botrytis cinerea and Golovinomyces cichoracearum (Powdery Mildew also doesn’t culture) so these microbes can be independently quantitated without complicating concordance with CFU counts.

For more information about Cq/CFU conversions:

Peer-reviewed studies have shown that qPCR testing methods, such as the PathoSEEK® Microbial Safety Testing Platform, are able to more accurately detect and quantify yeast and mold species present on a cannabis sample than culture-based methods. The PathoSEEK® Total Yeast and Mold test looks for a specific DNA sequence that exists in all yeasts and molds. Because of this, the PathoSEEK Total Yeast and Mold test can detect all yeast and mold species, regardless of whether they grow in culture. Culture-based tests can only detect the species that grow in a given medium and timeframe. Conversely, qPCR can more effectively exclude off-target microbial species, such as bacteria, which have been shown to grow in TYM culture medium.

Please download our validation document here: