P2-195 Single Marker Detection and Virulence Gene Profiling of STEC in Produce and Associated Farmscape Samples

Tuesday, July 11, 2017
Exhibit Hall (Tampa Convention Center)
Janneth Pinzon , University of California-Davis , Davis , CA
Kamieko Kayoshi , University of California-Davis , Davis , CA
Jeremy Roland , University of California-Davis , Davis , CA
Adrian Sbodio , University of California-Davis , Davis , CA
Bettina Groschel , Roka Bioscience , San Diego , CA
William Chaney , Roka Bioscience , San Diego , CA
Erin Dreyling , Roka Bioscience , Warren , NJ
Michele Jay-Russell , Western Center for Food Safety, University of California , Davis , CA
Trevor Suslow , University of California-Davis , Davis , CA
Introduction:  Available commercial systems designed for rapid presumptive screening for shiga-toxin producing E. coli target the stx and eae genes. Strains of clinical concern contain alternative mechanisms for virulence missed by reliance on the cardinal eae marker. Environmental STEC isolates containing less than the prerequisite complement of virulence traits are routinely detected on produce and the associated farmscape environment.

Purpose:  To further evaluate the potential utility of single marker technology for the detection of non-O157 STEC in the produce production environment and to investigate the confirmatory presence of virulence genes in purified isolates.

Methods: 177 samples (basil, bok choy, leeks, kale, chard, collard, parsley, soil, sediments, and irrigation water) were collected in four seasonal samplings. Bacteria were captured by filtration using Modified Moore Swabs and enriched in Tryptic Soy Broth-novobiocin, and incubated for 24 h at 42°C. Enrichments were screened with the Atlas® STEC EG2 Combo Detection Assay and cultural isolation conducted. A multiplex MXPCR for E. coli 16s rDNA, stx1, stx2, and eae gene targets was used for initial characterization. Positive strains were examined by PCR for seven virulence-associated genes. Known clinical non-O157 were reference standards.

Results:  52 (29.4%) samples were positive for STEC. Ten samples (5.6%) were positive for E. coli O157:H7. Basil showed a higher positive outcome (10.2%). Of 373 presumptive E. coli colonies purified, only 7 isolates (1.9%) were stx/eae positive, 34 (9.1%) and 44 (11.8%) were individually positive for stx and eae, respectively. Seventeen different marker profiles were obtained. Most of the STEC were isolated from positive enrichments, however isolates carrying stx and other virulence genes (ehxA, adfO)were recovered from negative samples.

Significance: This study contributes to a larger longer‐term effort to clarify the risk associated with the diverse STEC group and its application to routine compliance and lot acceptance testing for fresh produce.