Abstract
More than 400 serotypes of Shiga toxin-producing Escherichia coli (STEC) have been implicated in outbreaks and sporadic human diseases. In recent years STEC strains belonging to serogroup O178 have been commonly isolated from cattle and food of bovine origin in South America and Europe. In order to explore the significance of these STEC strains as potential human pathogens, 74 German and Argentinean E. coli O178 strains from animals, food and humans were characterized phenotypically and investigated for their serotypes, stx-genotypes and 43 virulence-associated markers by a real-time PCR-microarray. The majority (n = 66) of the O178 strains belonged to serotype O178:H19. The remaining strains divided into O178:H7 (n = 6), O178:H10 (n = 1), and O178:H16 (n = 1). STEC O178:H19 strains were mainly isolated from cattle and food of bovine origin, but one strain was from a patient with hemolytic uremic syndrome (HUS). Genotyping of the STEC O178:H19 strains by pulsed-field gel electrophoresis revealed two major clusters of genetically highly related strains which differ in their stx-genotypes and non-Stx putative virulence traits, including adhesins, toxins, and serine-proteases. Cluster A-strains including the HUS-strain (n = 35) carried genes associated with severe disease in humans (stx2a, stx2d, ehxA, saa, subAB1, lpfAO113, terE combined with stx1a, espP, iha). Cluster B-strains (n = 26) showed a limited repertoire of virulence genes (stx2c, pagC, lpfAO113, espP, iha). Among O178:H7 strains isolated from deer meat and patients with uncomplicated disease a new STEC variant was detected that is associated with the genotype stx1c/stx2b/ehxA/subAB2/espI/[terE]/espP/iha. None of the STEC O178 strains was positive for locus of enterocyte effacement (LEE)- and nle-genes. Results indicate that STEC O178:H19 strains belong to the growing group of LEE-negative STEC that should be considered with respect to their potential to cause diseases in humans.
Highlights
Shiga toxin-producing Escherichia coli (STEC) is a zoonotic pathogen of significant public health concern
Our results indicate that STEC O178:H19 belong to the growing group of LEEnegative strains that are able to cause severe illness in humans (Newton et al, 2009)
Over the past years, STEC O178:H19 became one of the most prevalent serotypes isolated from dairy cows (Fernandez et al, 2010) and beef cattle (Tanaro et al, 2012) as well as in beef abattoirs (Masana et al, 2011) and in food of bovine origin in Argentina and Germany (Beutin et al, 2007; Sanz et al, 2007; Werber et al, 2008; Slanec et al, 2009; Kruger et al, 2011)
Summary
Shiga toxin-producing Escherichia coli (STEC) is a zoonotic pathogen of significant public health concern. STEC has been associated with both outbreaks and sporadic cases of human disease, ranging from mild diarrhea to hemorrhagic colitis (HC) and life-threatening hemolytic uremic syndrome (HUS) (Melton-Celsa et al, 2012). STEC strains produce one or both of two major types of potent cytotoxins called Shiga toxins Stx and Stx, which function as primary virulence factors in human disease. The more homogenous Stx family consists of Stx1a, Stx1c, and Stx1d. The more heterogeneous Stx family comprises Stx2a and the variants designated Stx2b, Stx2c, Stx2d, Stx2e, Stx2f, and Stx2g (Scheutz et al, 2012). Stx2d differs from all known Stx types because it is activated in its biological activity by elastase, a constituent of the intestinal mucus (Melton-Celsa et al, 1996)
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