Relative Cytotoxicity ofEscherichia coliO157:H7 Isolates from Beef Cattle and Humans

Abstract

Differences and similarities between Escherichia coli O157:H7 isolates from beef cattle and those from sporadic human outbreaks are not fully elucidated. Here, we compared 44 O157:H7 isolates of bovine and human origins (22 isolates of each) to better understand their cytotoxic potential. The Shiga toxin genes stx1, stx2, or both were detected in the 44 isolates, and all elicited Vero cell cytotoxicity. The greatest cytotoxicity was caused by bovine isolates having only stx2 and which represented the majority of such isolates (81.8%). However, no correlation was found between the level of stx gene transcription and cytotoxicity. All human and bovine isolates possessed variant type stx2 and stx2c, respectively, as determined by PCR-restriction fragment length polymorphism. Isolates harboring both stx1 and stx2 genes were much more frequent in human isolates (86.4%). The combination stx1-stx2c found in only four bovine isolates was less cytotoxic. It is clear that cytotoxicity alone cannot account for the apparent inability of O157:H7 bovine isolates to cause diseases in humans. We have found that stx1-stx2-containing or stx1-stx2c-containing isolates were less cytotoxic than several bovine isolates having only stx2c, suggesting that the stx gene combination or other virulence genes in specific genetic lineages may affect the disease outcome.

Detection of virulent Escherichia coli O157 strains using multiplex PCR and single base sequencing for SNP characterization

“…Also previous studies have observed differences in stx status between human and non-human bacterial strains. However, they observed, in part, different stx patterns than in our study (Fegan and Desmarchelier 2002;Roldgaard et al 2004;Lefebvre et al 2009;Aspan and Eriksson 2010). This is in contrast to the study by Bono et al (2007), which found that stx1 and stx2 status were independent of human or bovine origin.…”

“…However, they observed, in part, different stx patterns than in our study (Fegan and Desmarchelier 2002; Roldgaard et al. 2004; Lefebvre et al. 2009; Aspan and Eriksson 2010).…”

Differential Virulence of Clinical and Bovine-Biased Enterohemorrhagic Escherichia coli O157:H7 Genotypes in Piglet and Dutch Belted Rabbit Models

“…Several studies have found an association between the amount of Stx produced and/or the type of stx gene present and the virulence of EHEC O157 strains (3,17,39,43,48). The results presented here suggest that the presence of the stx 2 gene and/or production of higher amounts of Stx may contribute to the increased virulence of CG strains.…”

Carriage of stx2a Differentiates Clinical and Bovine-Biased Strains of Escherichia coli O157

“…Several of these epidemiological studies [41], [42], [43], [45], [46], [47], [48] demonstrated that EHEC O157 carrying stx2a (with or without stx2c ) rather than stx2c were more frequent among clinical isolates, in agreement with the results presented here. Recently, Kawano et al [48] along with others [43], [45], [46] suggested that EHEC O157 carrying stx2c were associated with asymptomatic individuals and mild disease however it is also isolated from patients with severe disease (bloody diarrhea, HC and HUS) as shown by others [23], [40], [41], [44], [47], [49]. Furthermore, Fuller et al recently demonstrated that purified Stx2a is more potent than Stx2c against primary human kidney cell lines and in mouse models [42].…”

“…Other studies have evaluated association of stx2a and stx2c content with human virulence [23], [40], [41], [42], [43], [44], [45], [46], [47], [48], [49]. Several of these epidemiological studies [41], [42], [43], [45], [46], [47], [48] demonstrated that EHEC O157 carrying stx2a (with or without stx2c ) rather than stx2c were more frequent among clinical isolates, in agreement with the results presented here.…”