Antimicrobial resistance in Shiga toxin-producing Escherichia coli O157 and O26 isolates from beef cattle.

This study was conducted to determine the prevalence of antimicrobial resistance in Shiga toxin-producing Escherichia coli (STEC) O157 (n = 241) and O26 (n = 11) isolated from beef cattle and to characterize their antimicrobial resistance profiles. Resistance to dihydrostreptomycin was detected most frequently (STEC O157, 9.5%; STEC O26, 54.5%), followed by resistance to oxytetracycline (7.9%; 45.5%) and ampicillin (5.4%; 36.4%). Resistance to one or more antimicrobial agents was detected in 13.3% (32/241) of the STEC O157 isolates and 54.5% (6/11) of the STEC O26 isolates. The antimicrobial resistance rate in the STEC O26 isolates was significantly higher than that in the STEC O157 isolates (P = 0.002, Fisher's exact test). The antimicrobial resistance rate in the STEC O157 isolates possessing both stx(1) and stx(2) genes was 26.3% (15/57), while that in the isolates possessing stx(2c) gene alone was 3.9% (3/77). These findings suggest that the antimicrobial resistance in STEC O157 is associated with serogroups and the Shiga toxin genotype.