Occurrence and characterisation of enterohaemorrhagic Escherichia coli isolates from diarrhoeic calves

The presence of major virulence factors of enterohaemorrhagic Escherichia coli (EHEC; stx1, stx2, eae, Ehly) were determined among isolates from 158 diarrhoeic calves by multiplex polymerase chain reaction (PCR). Strains positive for virulence factors were subjected to serotype specific PCR assays for O157:H7 and O111 antigens. Additionally, serogroups were determined by three monovalent antisera for O26, O111 and O157 somatic antigens and enterohaemolysin production were also shown phenotypically. Thirteen (8.2%) calves carried strains positive for one or more of the virulence factors tested, and eleven (6.9%) calves harboured the shiga toxin-producing strains (stx1 or stx2). stx1 was detected in eight (5%) and stx2 in three (1.9%) calves. eae and Ehly were observed in the same frequency (6.3%) and were detected in parallel. Of the 13 virulence-positive strains, the predominant genotype was (stx1/eae/Ehly) at 53.8%. None of the EHEC in this study belonged to O157:H7 or O111 serotypes, but four strains (30.7%) belonged to the O26 serogroup. The results show the possible role of stx1/eae in calf diarrhoea and the particular importance of O26 EHEC. Calves can also act as a reservoir for EHEC and in the transmission of the disease to humans.