Antibiotic resistance of Escherichia coli O157:H7 and O157:NM isolated from animals, food, and humans.

Antibiotic resistance was determined for 118 E. coli O157:H7 and 7 O157:NM isolates from animals, foods, and humans. Among the 125 isolates, 30 (24%) were resistant to at least one antibiotic and 24 (19%) were resistant to three or more antibiotics. Cattle isolates had the highest rate (34%) of antibiotic resistance. The seven resistant food isolates were all from ground beef. The most frequent resistance type overall was streptomycin-sulfisoxazole-tetracycline, which accounted for over 70% of the resistant strains. Two E. coli O157:NM isolates from cattle were resistant to six antibiotics: ampicillin, kanamycin, sulfisoxazole, streptomycin, tetracycline, and ticarcillin. Streptomycin was the most common antibiotic to which E. coli O157:H7 and O157:NM were resistant (29 out of 30 isolates), followed by tetracycline (26 isolates). This study suggests that E. coli O157:H7 and O157:NM have developed resistance to antibiotics. Research is needed to define mechanisms of antibiotic resistance in E. coli O157:H7 and to minimize the development of resistance.