Co-enrichment of Salmonella and STEC in Produce Matrices Prior to PCR Detection
Erica Miller 1, Daniel R. DeMarco 1 , J. David Legan 2 , Joelle Mosso 3 , Anke Liedek 4 , Laura Bleichner 4 , and Chris Crowe1
Eurofins Microbiology Laboratories, Inc.:1 Louisville, KY; 2 Madison, WI, 3 Fresno, CA; 4 Gold Standard Diagnostics, Freiburg, Germany
ABSTRACT
Introduction
Produce is routinely tested for Salmonella and STEC, but most commercial test kits require different enrichment conditions for the two pathogens, necessitating two samples and two separate workflows.
Purpose
To validate co enrichment of Salmonella using STEC enrichment conditions.
Methods
Produce samples (375 g) were artificially contaminated with Salmonella and/or STEC, and diluted 1/10 (mixed baby greens, parsley and cilantro mix, baby kale) or 1/5 (romaine lettuce and mixed leafy greens) using mTSB (without novobiocin). Samples were enriched at 41.5 C, and samples pulled at 10 and 24 hours, lysed, and tested using the BACGene™ Salmonella and BACGene STEC PCR kits, according to kit instructions. Additionally, asymmetric co enrichments were performed with Salmonella inoculated at 1 10 cfu and STEC inoculated at ~10 5 cfu to ensure that Salmonella would still be detectable despite a high
background of STEC.
Results
Mixed baby greens, parsley and cilantro, and baby kale were all inoculated at a high spike level of both STEC (6.9 cfu/375 g of E. coli O157) and Salmonella (7.4 cfu/375 g of S. enterica ser. Senftenberg) and all samples tested positive by PCR at 10 hours (n=7 samples per matrix). In follow up studies with mixed greens (n=3), S. enterica ser. Typhimurium inoculated at a low level either with or without STEC at high levels yielded PCR results at 10, 16, and 24 hours.
Significance
Co enrichment of Salmonella and STEC in mTSB for PCR testing will reduce produce sample amounts and streamline laboratory workflow and costs.
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