Antimicrobial Susceptibility Profiles of C. jejuni Isolated From Beef Cattle

Campylobacter jejuni is the most common cause of bacterial food borne illness world-wide. Although infection with C. jejuni is most commonly attributed to consumption of contaminated poultry, beef cattle may be another important source of infection. The University of Arizona conducted a longitudinal study to determine the presence of Campylobacter spp. in the cattle feedlot environment. Cattle fecal samples were collected at the range, feedlot arrival, 3 and 6 months, and at harvest.  Cattle were divided into two feed groups, with and without feed additives. Environmental samples were also collected from pens, flies, and birds. Thirty of these C. jejuni feedlot isolates were selected for antibiotic susceptibility testing based on the National Antimicrobial Resistance Monitoring System (NARMS) using tetracycline, clindamycin, ciprofloxacin, gentamicin, and erythromycin. Cultures were grown on Mueller Hinton blood agar to make a uniform lawn (1.0 MacFarland standard). Epsilometer (E test ^®) strips were placed radially on the lawn and incubated at 42°C/10%CO₂ for 48-72h. Results were recorded as minimum inhibitory concentrations (MICs). Preliminary results from 19 isolates show that four were resistant to tetracycline (MICs ranging from 24-256mg/ml), one isolate was resistant to clindamycin (MIC >8mg/ml), and one isolate was resistant to erythromycin (MIC>32mg/ml).  Thus far no difference in susceptibilities has been seen between the two feed groups. Resistance in isolates from cattle also changed over time, where strains isolated at 3 months differed in resistance at 6 months and at harvest.  Further testing may determine more differences in resistance over time and among the feed groups