Urease genes in non-O157 Shiga toxin-producing Escherichia coli: mostly silent but valuable markers for pathogenicity.

The distribution of ureC was investigated among 294 Escherichia coli isolates, comprising 72 strains from the E. coli standard reference collection (ECOR), 62 strains from the diarrhoeagenic E. coli (DEC) collection, and 160 clinical isolates of Shiga toxin-producing E. coli (STEC). The ureC gene was more frequent among STEC isolates harbouring eae than among those lacking eae (p < 0.0001). All clinical STEC isolates of serogroups O111 and O145 contained ureC, but only two of 294 isolates expressed urease activity. The silencing of urease expression could not be linked to a stop codon in ureD. The frequent occurrence of ure genes in eae-positive STEC isolates makes them valuable markers for virulence.