Running Aspergillus and Salmonella/STEC Assays from a Single Enrichment Using the MaGiC Lysis Kit
This article explains how to combine Aspergillus and Salmonella/STEC testing into a single PDB enrichment using the PathoSEEK MaGiC Lysis Kit workflow — and outlines the key limitations and deviations from our AOAC PTM-validated methods that labs must understand before implementing this protocol.
Overview
Traditionally, PathoSEEK Aspergillus and Salmonella/STEC assays require separate enrichments performed under different conditions. We have developed an alternate single-enrichment workflow that allows laboratories to run both assay types from one shared Potato Dextrose Broth (PDB) enrichment, reducing hands-on time and sample input requirements.
Click here to download the supplemental user guide
Important: This Protocol Is Not AOAC PTM-Validated
This is the most critical point to understand before implementing this workflow.
When run under their standard conditions, both the PathoSEEK Aspergillus Multiplex Detection Assay (AOAC PTM #072502) and the PathoSEEK Salmonella/STEC Multiplex Detection Assay (AOAC PTM #022202) are AOAC Performance Tested Methods certified. This single-enrichment protocol is not. It represents a laboratory-modified method, and as such:
- Your laboratory is responsible for demonstrating that this method is fit for its intended use prior to routine implementation.
- An internal method verification study is strongly recommended, as required by applicable state regulatory bodies and/or ISO/IEC 17025:2017.
- Results obtained using this workflow cannot be represented as being generated under an AOAC PTM-validated method.
Key Deviations from the Validated Methods
Before using this protocol, labs should be aware of the following specific departures from the validated workflows:
1. Free DNA Removal (Grim Reefer®) Is Not Performed The Grim Reefer free DNA removal step, which is part of the standard validated workflow, is not compatible with this single-enrichment protocol and must be omitted. Labs that rely on this step to manage environmental DNA background should factor this into their internal verification planning.
2. Extended Enrichment Time Required — Minimum 48 Hours This protocol requires a 48–54 hour enrichment period for all matrices, including dried cannabis flower. This is a longer window than the standard validated Aspergillus method (24–48 hours for flower) and substantially longer than the validated Salmonella/STEC method (16–24 hours). Labs should update their scheduling and SOPs accordingly.
3. Enrichment Broth Both Aspergillus and Salmonella/STEC enrichments are performed in Potato Dextrose Broth (PDB) rather than Tryptic Soy Broth (TSB) for Salmonella/STEC, or PDB supplemented with chloramphenicol for Aspergillus.
4. Increased Sample Input Volume for Salmonella/STEC Lysis The lysis input volume for Salmonella/STEC testing is 50 µL of enriched culture, compared to 10 µL in the validated method.
Who Should Use This Protocol?
This workflow may be appropriate for laboratories looking to streamline their cannabis microbial testing throughput. However, it is best suited for labs that:
- Have completed or are prepared to conduct an internal method verification study
- Operate in jurisdictions where laboratory-modified methods are permissible with proper validation documentation
- Understand and can communicate to clients that results are not generated under an AOAC PTM-validated workflow
Medicinal Genomics conducted a small validation study comparing the AOAC dual-enrichment method to a single-enrichment approach. If you’re interested in reviewing the data or the validation study design, please contact us at support@medicinalgenomics.com