Abstract
Deadly outbreaks and illnesses due to Shiga toxin-producing Escherichia coli (STEC) occur worldwide; however, the cultivation methods required for adequate monitoring and traceback investigations are inefficient at best. Detection of STEC relies heavily on enrichment; yet no standard media or protocols exist. Furthermore, whether enrichment may bias detection of multiple STEC serogroups from complex samples is unknown. Thus, 14 STEC strains of serogroups O157 and the top six non-O157s (O26, O45, O103, O111, O121, and O145) were enriched in pairs for 6–78 h in broth and evaluated by quantitative polymerase chain reaction (qPCR). Here we show that a conventional 6-h enrichment protocol did not result in intra-species culture bias for the isolates tested. However, subsequent enrichments often produced biased cultures, with differences in the qPCR gene copy number ≥2 log10apparent in 12%, 38%, and 52% of competitions after 30, 54, and 78 h of consecutive enrichments, respectively. Some strains were able to prevail and (or) out-compete the opponent strain in 100% of competitions. Our results suggest that culture bias should be considered and (or) evaluated further due to the potential implications during routine pathogen screening and outbreak investigations.
Highlights
Received: February 9, 2016Accepted: May 17, 2016Published: August 17, 2016Published by: Canadian Science PublishingInfection with Shiga toxin-producing Escherichia coli (STEC) ranges from mild to severe and can include diarrhea, hemorrhagic colitis, hemolytic uremic syndrome, and death
E. coli O157:H7 has been subjected to international reporting for nearly two decades, the most prevalent non-O157 serogroups have only recently gained attention (Gill and Gill 2010)
Over 435 STEC serotypes have been isolated from cattle, of which 12–17% are associated with human illness (Mathusa et al 2010; Kaspar et al 2010)
Summary
Infection with Shiga toxin-producing Escherichia coli (STEC) ranges from mild to severe and can include diarrhea, hemorrhagic colitis, hemolytic uremic syndrome, and death. Over 435 STEC serotypes have been isolated from cattle (the main reservoir of these pathogens), of which 12–17% are associated with human illness (Mathusa et al 2010; Kaspar et al 2010). To exceed the threshold of detection, isolation requires enrichment and selective media. Enrichment can increase cell numbers to achieve a detectable level in both culture and molecular-based assays (at least 100 cells/g food or feces) (Possé et al 2008; Bai et al 2012; Paddock et al 2012). Standard detection procedures and selective media have been developed for O157-STEC; no gold standard for the cultivation
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