Pathogenic and phylogenetic characteristics of non-O157 Shiga toxin-producing Escherichia coli isolates from retail meats in South Korea

ABSTRACT

Herein, we report the pathogenic and phylogenetic characteristics of seven Shiga toxin (Stx)-producing Escherichia coli (STEC) isolates from 434 retail meats collected in Korea during 2006 to 2012. The experimental analyses revealed that all isolates (i) were identified as non-O157 STEC, including O91H14 (3 isolates), O121H10 (2 isolates), O91H21 (1 isolate), and O18H20 (1 isolate), (ii) carried diverse Stx subtype genes (stx₁, stx(2c), stx(2e), or stx₁ + stx(2b)) whose expression levels varied strain by strain, and (iii) lacked the locus of enterocyte effacement (LEE) pathogenicity island, a major virulence factor of STEC, but they possessed one or more alternative virulence genes encoding cytotoxins (Cdt and SubAB) and/or adhesins (Saa, Iha, and EcpA). Notably, a significant heterogeneity in glutamate-induced acid resistance was observed among the STEC isolates (p < 0.05). In addition, phylogenetic analyses demonstrated that all three STEC O91H14 isolates were categorized into sequence type (ST) 33, of which two beef isolates were identical in their pulsotypes. Similar results were observed with two O121H10 pork isolates (ST641; 88.2% similarity). Interestingly, 96.0% of the 100 human STEC isolates collected in Korea during 2003 to 2014 were serotyped as O91H14, and the ST33 lineage was confirmed in approximately 72.2% (13/18 isolates) of human STEC O91H14 isolates from diarrheal patients.