Antimicrobial resistance patterns of Campylobacter from feedlot cattle

Aims: This study examined 448 Campylobacter strains isolated in 1999 and 2000 from US feedlot cattle for resistance to 12 antimicrobials. Methods and Results: Isolates were tested for antimicrobial susceptibility using the E-test method. Approximately 60% (n = 267) were resistant to one or more antimicrobials, and 19.6% (n = 88) were resistant to two or more antimicrobials. Of the Campylobacter jejuni isolates, 49.1% (n = 187) were resistant to tetracycline, 10.2% (n = 39) were resistant to nalidixic acid, 8.4% were resistant to trimethoprim/sulfamethoxazole, and 1.8% (n = 7) were resistant to ciprofloxacin. Resistance to any of the other eight antimicrobials was 1.3% or less, but 14.4% (n = 55) were resistant to two or more antimicrobials. In the Campylobacter coli group, 65.7% (n = 44) were resistant to tetracycline, 52.2% (n = 35) were resistant to trimethoprim/sulfamethoxazole, 22.4% (n = 15) were resistant to nalidixic acid, and 9.0% (n = 6) were resistant to ciprofloxacin. Resistance to any of the remaining eight antimicrobials was 3.0% or less, although 49.3% (n = 33) were resistant to two or more antimicrobials. Conclusions: Although antimicrobials are widely used in US feedlot cattle production, our results demonstrate generally low levels of resistance to a broad range of commonly used antimicrobials relative to other recent studies. Significance and Impact of the Study: Resistance data on Campylobacter isolated from this major US livestock commodity is lacking. This overview enhances current knowledge and provides a basis for further studies.