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P3-12 Molecular Serotyping of Shiga Toxin-producing Escherichia coli from Fresh Produce Enrichments Using FDA-ECID Microarray

Tuesday, July 28, 2015
Hall B (Oregon Convention Center)
Isha Patel , U.S. Food and Drug Administration , Laurel , MD
Jayanthi Gangiredla , U.S. Food and Drug Administration , Laurel , MD
Venugopal Sathyamoorthy , U.S. Food and Drug Administration , Laurel , MD
Seongeun Hwang , U.S. Food and Drug Administration , Laurel , MD
Christopher Elkins , U.S. Food and Drug Administration , Laurel , MD
Keith Lampel , U.S. Food and Drug Administration , Laurel , MD
Introduction: Fresh produce contaminated with Shiga Toxin-producing E. coli (STEC) has been implicated in a number of foodborne outbreaks.  There are over two hundred STEC serotypes, but not all cause human illness, therefore, it is important to accurately identify the serotype and virulence capacity of the STEC isolates.

Purpose: In this study, the efficacy and sensitivity of a custom design FDA-ECID microarray to accurately determine the serotype of STECs directly from produce enrichments was assessed. Currently used methods can take up to two weeks to first isolate a pure isolate from fresh produce and subsequently be analyzed by serology.  The custom designed microarray is used to characterize all pathogenic E. coli including STECs through its molecular serotyping component and was used to detect STECs directly from enriched broths to minimize the time to a final result.

Methods: Produce was spiked with known CFU of E. coli O157:H7 following the BAM protocol. Total DNA was isolated from overnight enriched cultures and hybridized onto the FDA-ECID array. Molecular serotyping was performed using alleles from the fliC, wzx, and wzy genes that are represented on the array. For virulence determination different probe sets were used based on the eae alleles, stx1 and 2 genes, and other virulence factors. 

Results: E. coli O157:H7 was accurately typed using the FDA-ECID array when up to 50 - 100 CFU were present in the initial inoculum. Competition with the presence of Salmonella and Listeria when added with E. coli O157:H7 did not interfere with an accurate serotype determination.

Significance: Results show that the FDA-ECID array is an effective alternative to serology in serotyping environmental E. coli isolates. By minimizing the time to results from two weeks to two days from overnight enrichments can help to reduce the overall analysis time for food samples.

Back to: Poster Session 3 – Laboratory and Detection Methods, Sanitation; Antimicrobials; Produce; Epidemiology
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