Ciprofloxacin resistance in E. coli isolated from turkeys in Great Britain

Fluoroquinolones are a widely used group of antimicrobials in both human and animal medicine, with ciprofloxacin being a critically important fluoroquinolone for serious human infections. The present study reports on a 1-year survey for the presence of ciprofloxacin-resistant Escherichia coli in turkeys from Great Britain. Boot swabs were taken from 442 turkey flocks comprised of 125 breeding flocks and 317 meat flocks from 337 different farms over a 1-year period (2006 to 2007). CHROMagar ECC containing 1 mg/l ciprofloxacin was used to obtain ciprofloxacin-resistant isolates. Isolates were tested for sensitivity to 16 different antimicrobials. Isolates with ciprofloxacin minimum inhibitory concentrations ≥8 mg/l were tested for mutations in gyrA by polymerase chain reaction and DNA sequencing. Selected isolates were tested by multiplex polymerase chain reaction for qnrA, qnrB and qnrS, qepA and aac(6')-Ib-cr genes. Conjugations were performed to assess the transferability of resistance to quinolones. Ciprofloxacin-resistant E. coli was found in 22.4% of turkey breeding flocks and 60.9% of meat flocks. Two main mutations in gyrA, as well as a range of silent mutations, were identified in resistant isolates. Flocks with transferable resistance genes qnrB, qnrS, and aac(6')-Ib-cr were found at a low flock prevalence of 4.2%, 1.6% and 1.0%, respectively; however, under laboratory conditions only transfer of qnrS genes could be demonstrated. This work has confirmed the occurrence of ciprofloxacin-resistant E. coli strains throughout turkey breeding and meat flocks, with almost one-third of E. coli isolates being resistant to ciprofloxacin. Of those, more than 87% were also resistant to three or more antimicrobial classes.