Characterization of Shiga toxin producing E-coli and O157 serotype E-coli isolated in France from healthy domestic cattle

A study was carried out in France in collaboration with the meat industry t o investigate the occurrence and characteristics of Shiga toxin-producing E , coli (STEC) and O157 E. coli in a population of healthy bovines represent ative of French livestock. A total of 851 animals belonging to three bovine classes (106 young bulls, 374 dairy cows and 371 meat cows) were included in the study. Samples of feces and of the corresponding carcasses were coll ected from March 97 to August 97 in seven abattoirs spread throughout the n ational territory. STEC cultures from the 1702 samples were screened using PCR for the presence of stx genes. Positive samples were further subjected to colony blot hybridization and to O157-specific immunomagnetic separation . Probe-positive colonies and O157 colonies were then analyzed for the pres ence of virulence genes and phenotypic characters (serotype, Stx production ). In 154 (18.1%) feces and 91 (10.7%) carcass samples stx genes were detec ted. Two hundred and twenty-two STEC colonies were isolated from 67 (7.9%) feces and 16 (1.9%) carcass samples, with 183 STEC isolated from feces and 39 from carcasses. Only eight O157 isolates were collected from feces sampl es. None of these O157 E. coli isolates presented stx genes and thus could not be considered as pathogenic regarding hemorrhagic colitis (HC) and hemo lytic uremic syndrome (HUS). In 3.2% of STEC isolated from feces and in 10. 2% of STEC from carcasses eae genes were detected. In 17% of STEC from fece s and in 30.7% from carcasses ehx genes were detected. Using these data, th e 222 STEC colonies could be classified in 11 different 'virulence patterns ' (presence/absence of stx1, stx2, eae and ehx genes), showing that more th an 77% of isolates presented only one virulence factor. Only three STEC on 222 colonies (1.3%) presented the three virulence factors stx, eae and ehx in association, none of them reacting with antisera specific for enterohemo rrhagic E, coli. (EHEC). These data, together with the fact that only five isolates on the 222 (2.2%) reacted with such antisera (three O111 and two O 26 isolates) demonstrated that the natural bacterial populations isolated d uring this study were clearly distinct from EHEC. (C) 2001 Elsevier Science B.V. All rights reserved.