Prevalence of Hemolysin Genes and Comparison of ehxA Subtype Patterns in Shiga Toxin-Producing Escherichia coli (STEC) and Non-STEC Strains from Clinical, Food, and Animal Sources

Abstract

c Shiga toxin-producing Escherichia coli (STEC) belonging to certain serogroups (e.g., O157 and O26) can cause serious conditions like hemolytic-uremic syndrome (HUS), but other strains might be equally pathogenic. While virulence factors, like stx and eae, have been well studied, little is known about the prevalence of the E. coli hemolysin genes (hlyA, ehxA, e-hlyA, and sheA) in association with these factors. Hemolysins are potential virulence factors, and ehxA and hlyA have been associated with human illness, but the significance of sheA is unknown. Hence, 435 E. coli strains belonging to 62 different O serogroups were characterized to investigate gene presence and phenotypic expression of hemolysis. We further investigated ehxA subtype patterns in E. coli isolates from clinical, animal, and food sources. While sheA and ehxA were widely distributed, e-hlyA and hlyA were rarely found. Most strains (86.7%) were hemolytic, and significantly more hemolytic (95%) than nonhemolytic strains (49%) carried stx and/or eae (P < 0.0001). ehxA subtyping, as performed by using PCR in combination with restriction fragment length polymorphism analysis, resulted in six closely related subtypes (>94.2%), with subtypes A/D being eae-negative STECs and subtypes B, C, E, and F eae positive. Unexpectedly, ehxA subtype patterns differed significantly between isolates collected from different sources (P < 0.0001), suggesting that simple linear models of exposure and transmission need modification; animal isolates carried mostly subtypes A/C (39.3%/42.9%), food isolates carried mainly subtype A (81.9%), and clinical isolates carried mainly subtype C (66.4%). Certain O serogroups correlated with particular ehxA subtypes: subtype A with O104, O113, and O8; B exclusively with O157; C with O26, O111, and O121.

Molecular Profiling of Shiga Toxin-Producing Escherichia coli and Enteropathogenic E. coli Strains Isolated from French Coastal Environments

“…These include, for example, the enterohemolysin, encoded by the ehxA gene, which is linked to cytotoxic effects on endothelial cells (24), the enteroaggregative E. coli (EAEC) heat-stable enterotoxin, encoded by the astA gene (25), and the alpha-hemolysin, encoded by the hlyA gene (26).…”

Plasmids from Shiga Toxin-Producing Escherichia coli Strains with Rare Enterohemolysin Gene ( ehxA ) Subtypes Reveal Pathogenicity Potential and Display a Novel Evolutionary Path

“…ehxA subtypes of plasmids sequenced in this study were previously identified by PCR-RFLP (32,41). ehxA subtypes of previously sequenced E. coli plasmids used for comparative analysis in the current study (Table 1) were identified using the CLC Genomics Workbench restriction site analysis tool.…”

“…The bacterial strains used in this study are listed in Table 1. Strains CFSAN004176 to CFSAN004181 have been described previously as 03-3375, 05-3014, 06-00048, 08-00022, 09-00049, and USMARC_GB_STEC_089, respectively (32).…”

“…The fact that subtype D strains segregate away from all of the other subtypes suggests that these STEC strains may carry significantly different plasmids than those previously identified and characterized. Moreover, our previous analyses of 435 E. coli strains isolated from animal, food, environmental, and clinical (human) sources identified only four ehxA subtype D strains, which were all food isolates (32). These particular STEC strains had not been implicated in human disease, but the rarity of these isotypes in this population further suggested that these may be unique E. coli strains.…”

“…To date, six ehxA subtypes have been identified using PCR in combination with restriction fragment length polymorphism (RFLP) analysis. These ehxA subtypes have been shown to phylogenetically cluster into eae-positive (subtypes B, C, and F), a mix of eae-positive (subtype E) and eae-negative (subtype A), and a third, most distantly related, cluster of eae-negative (subtype D) STEC strains (31,32). The fact that subtype D strains segregate away from all of the other subtypes suggests that these STEC strains may carry significantly different plasmids than those previously identified and characterized.…”