Virulence genes in verocytotoxigenic Escherichia coli strains isolated from humans and cattle

Verocytotoxigenic Escherichia coli (VTEC) causing diarrhoea, haemorrhagic colitis and haemolytic-uremic syndrome usually have additional traits such as the adhesin intimin and a large plasmid that seems to increase virulence. There are, however, isolates of VTEC causing serious symptoms that do not harbour these traits. In the present study we have used PCR with primers detecting adhesin genes other than eaeA, namely fimA, papC, sfaD/sfaE and daaE. We have also used PCR to detect the genes hlyA and iutA that besides the plasmid-borne gene E-hly possibly support the bacterial access to iron. The aim of the study was to identify and compare the presence of virulence genes in VTEC isolates of human and cattle origin. The main finding was that the absence of E-hly might be compensated for by the gene iutA coding for aerobactin or hlyA coding for alpha-haemolysin as 94% of the human VTEC isolates had at least one of these genes. Interestingly, only 45% of VTEC isolated from cattle had any of these genes. We propose that this might be the reason for the relatively low incidence of symptomatic VTEC infections among humans in relation to the high number of VTEC among cattle.