Location: Produce Safety and Microbiology ResearchTitle: Selective recovery by different culture methods of Shiga toxin-producing Escherichia coli genotypes from a major produce production region in California(Abstract)) Author
|Cooley, Michael - Mike|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/22/2012
Publication Date: N/A
Citation: Interpretive Summary:
Technical Abstract: The higher consumption of fresh fruits and vegetables in the United States has corresponded to an increase in the number of outbreaks. More than 45% of the leafy greens-associated outbreaks of Shiga toxin-producing Escherichia coli (STEC) O157:H7 have been linked to produce from California’s central coast. To develop improved methods for the efficient recovery of serotype O157:H7 and other non-O157 STEC, we analyzed the genetic composition of isolates recovered from multiple animal and environmental samples on three different selective media. Samples were subjected to a non-selective enrichment with O157-immunomagnetic beads, followed by plating on Rainbow O157 agar or modified sheep’s blood agar (SBA). The enriched samples were plated also on CHROMagar O157 media. Suspect STEC colonies, based on distinctive colony morphology, were genotyped by using PCR and the ampliPHOX colorimetric technology with a low-density DNA microarray, designed to target O-antigen serogroups and effectors, associated with STEC virulence. O-antigen genotyping results identified serogroups O26, O45, O91, O103, O104, O111, O113, O128, O145, and O157 in isolates from one or more of the three selection media. Additionally, over 74% of the STEC isolates from any of the selection media were positive for the hemolysis genes ehxA, hlyA and/or sheA. Autoagglutinating adhesin (saa) or subtilase cytotoxin (subA) were detected in 77% and 57% of the STEC isolates from SBA, respectively, in contrast to the < 15% of the isolates from Rainbow O157 and CHROMagar O157 media. Approximately, 30% of the isolates were positive for both stx1 and stx2. However, 38% of the isolates from Rainbow agar were also stx2g-positive in contrast to <1% of the isolates from CHROMagar O157 and SBA being stx2g-positive. Interestingly, >66% of the STEC isolates recovered on Rainbow agar were positive for intimin (eae) and the non-enterocyte effacement effectors, nleA, nleB, nleH1-2, or ent/espL2. Our findings revealed evidence of culture bias and emphasized the advantage of using different selection methods and media for the efficient isolation of STEC from environmental samples.