Abstract
Over a 2-year period, from January 2011 to May 2013, a total of 1094 faecal swab samples were collected from cattle at different age at 4 farms in North Bulgaria: Okorsh, Slavyanovo (Popovo municipality), Dobri dol and Trem. Out of them, 36 coli strains (3.3%) positive in the E. coli O:157 antiserum agglutination test and identified by the BBL CRYSTAL identification system as belonging to the E. coli O:157 serotype were isolated. The distribution of isolates was as followed: 5 (0.5%) E. coli O:157 strains at the Okorsh dairy cattle farm, 7 (0.6%) E. coli isolates at the Slavyanovo dairy farm, 16 (1.5%) isolates at the Dobri dol farm and 8 (0.7%) isolates at the Trem farm. Colibacteria exhibited 100% sensitivity to oxyimino-cephalosporins, gentamicin and enrofloxacin, and were resistant to ampicillin (19.4%) and tetracycline (41.6%). From the 15 strains resistant to tetracycline, 11 were isolated from the cows at Dobri dol, while the other 4 originated from the other three farms. The 7 ampicillin-resistant E. coli isolates were detected only at the Dobri dol cattle farm.