Structural and functional differences between disease-associated genes of enterohaemorrhagic Escherichia coli O111

We analysed 72 clinical isolates of enterohaemorrhagic Escherichia coli (EHEC) O111 from patients with diarrhoea or haemolytic uraemic syndrome (HUS) isolated during the period from 1955 to 2005 and identified six motile strains (flagellar antigens 8, 10 and 11); the remaining 66 (92%) were nonmotile (NM) and could not be typed by conventional H serotyping. To improve subtyping methodologies, we determined genotypes of the flagellin-encoding fliC. Three fliC genotypes were found which were identical to those of motile EHEC O111 with H antigens 8, 10 and 11 and designated fliCH8, fliCH10 and fliCH11. The IS629 insertion element was present, identically located, in six epidemiologically unrelated isolates with fliCH8. The prevalence of the fliC genotypes in the 72 EHEC O111 strains were fliCH8 (89%), fliCH10 (7%) and fliCH11 (4%). Within these fliC genotypes, a high degree of homogeneity for the presence of disease-associated genes was found. The adhesins-encoding genes eae and efa-1 were present in all strains with fliCH8 and fliCH11, but absent from strains with fliCH10. The latter strains have not been reported previously. Strains with fliCH10 and fliCH11, but not those with fliCH8, retained intact cadA and cadC loci and decarboxylated lysine. Three different stx genotypes including stx1, stx2 and stx1/stx2 were determined among the 72 EHEC O111. We observed a significant increase over time in the frequency of strains harbouring both stx1 and stx2. The presence of stx2 both alone and in combination with stx1 was significantly (χ2=23.16χ2=23.16, P<0.00001, CI95 [2.29; 9.76]) associated with HUS. Therefore, the emergence of EHEC O111 should be monitored carefully. We conclude that EHEC O111 strains can be differentiated using specific loci required for motility, adherence, Stx production, and lysine decarboxylation. The divergence within EHEC O111 makes it possible to subtype these emerging pathogens in the laboratory thereby providing a basis for further investigations into their ecological niches and survival capabilities.