Antimicrobial susceptibilities of Escherichia coli strains from a turkey operation

Objective—To measure minimum inhibitory concentrations (MIC) of 17 antimicrobials for Escherichia coli isolates from a turkey operation and assess whether small samples provide precise estimates of geometric mean MIC. Design—Prospective study. Sample Population—105 clinical isolates from birds and 1,104 fecal isolates from 20 flocks (poults and finisher hens). Procedure—A Mueller-Hinton broth dilution panel was used to measure MIC, and MIC of fecal and clinical isolates were compared. We drew random samples of 5, 10, 15, 20, 25, 30, 35, 40, and 45 isolates from each finisher flock and between 100 and 105 isolates from 5, 7, 10, and 20 flocks. Antimicrobial usage was determined for enrolled flocks. Results—Six of 12 poult and 18 of 20 finisher flocks had been treated with antimicrobials, often for respiratory illnesses consistent with colibacillosis. All birds received gentamicin at the hatchery. More fecal than clinical isolates were resistant to ampicillin; however, more clinical isolates were resistant ...