Scientific Publications by FDA Staff

Appl Environ Microbiol 2013 Oct;79(20):6301-11

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.

Lorenz SC, Son I, Maounounen-Laasri A, Lin A, Fischer M, Kase JA

Shiga toxin producing Escherichia coli (STEC) belonging to certain serogroups (e.g. O157, 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 E. coli hemolysin genes (hlyA, ehxA, ehlyA, 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, ehlyA and hlyA were found rarely. 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 PCR-RFLP, resulted in six closely related subtypes (> 94.2%), with A/D being eae-negative STECs and B, C, E and F eae-positive. Unexpectedly, ehxA subtype patterns differed significantly between isolates collected from different sources (P < 0.0001), suggesting simple linear models of exposure and transmission need modification; animal isolates carried mostly subtypes A/C (39.3%/42.9%), food isolates mainly subtype A (81.9%) and clinical isolates subtype C (66.4%). Certain O serogroups correlated with particular ehxA subtypes, subtype A with O104, O113 and O8, B exclusively with O157 and C with O26, O111 and O121.