PREVALENCE AND CHARACTERISTICS OF HUMAN AND BOVINE VEROTOXIGENIC ESCHERICHIA-COLI STRAINS ISOLATED IN GALICIA (NORTH-WESTERN SPAIN)

An epidemiological study was carried out to determine the incidence an d the serotypes of verotoxigenic Escherichia coli (VTEC) that cause in fections in Galicia (north-western Spain). Although, VTEC strains were isolated from 55 (14%) of the 387 calves sampled and the majority of bovine VTEC strains belonged to serotypes (O26:H11 or H-, O91:H21, O10 3:H2, O105:H18, O111:H-, O113:H21, O126:H-, O128:H- and O157:H7 or H-) previously associated with human haemorrhagic colitis (HC) and haemol ytic uraemic syndrome (HUS) in other countries, VTEC are not a common cause of human infections in Spain. Thus, VTEC (O26:H11 and O86:H10) w ere isolated from only 3 (0.6%) of the 482 children with diarrhoea inv estigated. We examined the 69 (3 humans and 66 bovines) VTEC strains t hat were initially isolated as E. coli producing a toxin cytotoxic to Vero and HeLa cells by polymerase chain reaction (PCR) using specific primers for VT1, VT2 and eae genes. PCR showed that 38 (55%) of VTEC s trains carried VT1 genes, 18 (26%) possessed VT2 genes, and 10 (14%) c arried both VT1 and VT2 genes. Three (one human and two bovine) strain s which were formerly VTEC had lost the ability to produce verotoxins upon subculture and became negative for VT1 and VT2 by PCR. In total 3 5 (51%) of 69 VTEC strains, including the two human VT1(+) strains of serotype O26:Hll, were positive for eae sequences when tested by PCR. Presence of the eae gene was significantly more frequent (100%; 21/21) among VTEC strains with serotypes (O26:Hll, O111:H-, O157:Hand O157:H 7) considered as enterohaemorrhagic E. coli (EHEC) than among VTEC str ains with non-EHEC serotypes (29%; 14/48) (p < 0.001). Results obtaine d in this study Indicate that cattle may be an important source of VTE C involved in human disease. However, severe clinical syndromes caused by VTEC, such as HC and HUS, are uncommon in Spain, in comparison wit h North America and the UK. In any case, VTEC disease can appear on th e scene very suddenly, as occurred in the UK and North America in the 1980s.