Heterogeneity of shiga toxin-producing Escherichia coli strains isolated from hemolytic-uremic syndrome patients, cattle, and food samples in centralFrance

A detailed analysis of the molecular epidemiology of non-O157:H7 Shiga toxi n-producing Escherichia call (STEC) was performed by using isolates from sp oradic cases of hemolytic-uremic syndrome (HUS), animal reservoirs, and foo d products, The isolates belonged to the O91 and OX3 serogroups and were co llected in the same geographical area over a short period of time. Five typ ing methods were used; some of these were used to explore potentially mobil e elements like the stx genes or the plasmids (stx(2)-restriction fragment length polymorphism [RFLP], stx, gene variant, and plasmid analyses), and o thers were used to study the whole genome (ribotyping and pulsed-field gel electrophoresis [PFGE]), The techniques revealed that there was great diver sity among the O91 and OX3 STEC strains isolated in central France. A close relationship between strains of the same serotype having the same virulenc e factor pattern was first suggested by ribotyping, However, stx(2)-RFLP an d stx(2) variant analyses differentiated all but 5 of 21 isolates, and plas mid analysis revealed further heterogeneity; a unique combination of charac teristics was obtained for all strains except two O91:H21 isolates from bee f. The latter strains were shown by PFGE to be the most closely related iso lates, with > 96% homology, and hence may be subtypes of the same strain. O verall, our results indicate that the combination of stx(2)-RFLP, stx, vari ant, and plasmid profile analyses is as powerful as PFGE for molecular inve stigation of STEC diversify. Finally, the non-O157:H7 STEC strains isolated from HUS patients were related to but not identical to those isolated from cattle and food samples in the same geographical area. The possibility tha t there are distinct lineages of non-O157:H7 STEC, some of which are more v irulent for humans, should be investigated further.