Detection of E. coli O157:H7 and Salmonella in a Cannabis Simulant Using a Liquid Crystal-based Immunoassay

Introduction: Patients using medicinal cannabis often have compromised immune systems.  Thus, E. coli O157:H7 and Salmonella, which can contaminate cannabis and cannabis-based products, pose a significant health risk to these patients.  To mitigate this risk, the current project developed a liquid crystal-based screening test for detection of E. coli O157:H7 and Salmonella in raw cannabis. The rapid screening (<16 hours to results) of a simulant of raw cannabis was developed using a single-stage enrichment.

Purpose: A liquid crystal-based assay was developed, tested, and compared against culture-based methods for detection of E. coli O157:H7 and Salmonella in a cannabis simulant.

Methods: A simulant of cannabis, hops (Humulus lupulus), was inoculated with low levels (<10 cells) of E. coli O157:H7 and Salmonella and permitted to stabilized overnight.  The samples were then enriched in mTSB+n and mTSB, respectively, for 15-24 hours. Detection was conducted in a liquid crystal-based detection platform and compared against cultures of the processed antibody-coated microspheres on Chromagar O157 (E. coli O157:H7) and XLT4 and Hektoen enteric agar (Salmonella).

Results: For E. coli O157:H7 testing, the liquid crystal-based assay correctly detected 96% (n= 23) of the culture positive samples and 93% (n= 15) of the non-inoculated or fractionally negative samples. For Salmonella, the assay correctly detected 92% (n= 25) of the culture positive samples and 96% (n= 25) of the non-inoculated and fractionally negative samples. Detection between the liquid crystal-based platform and the culture-based analysis showed similar results at low levels of inoculation.

Significance: This liquid crystal-based immunoassay provides a simple one-step enrichment and screening method for detection of E. coli O157:H7 and Salmonella in cannabis.