Identification of DNA Gyrase A Mutations in Ciprofloxacin-Resistant Isolates of Salmonella typhimurium from Men and Cattle in Germany

Six multiply resistant isolates of Salmonella typhimurium var. Copenhagen with high-level resistance to fluoroquinolones (e.g., MIC of ciprofloxacin: 32 μg/ml) were isolated from human patients ( n = 3) and from cattle ( n = 3). The isolates were examined by complementation tests using a set of broad-host-range plasmids, which carry either the gyr A + or the gyr B + genes or a combination of both from Escherichia coli K-12. The results indicated a combination of gyr A and gyr B mutations in all isolates. Subsequent direct sequencing of PCR-generated internal DNA fragments of gyr A revealed an identical double mutation in all six isolates (Ser83 → Ala and Asp-87 → Asn). In addition, the results of phenotypic (i.e., phagetype, biotype, serotype) and genotypic characterization [i.e., ribotyping and polymerase chain reaction fingerprinting (PCR-fingerprinting)] were identical for all six isolates and were distinguishable from a quinolone-susceptible strain of the same serovar and an unrelated isolate of S. typhimurium . These data indicate the clonal identity of the fluoroquinolone-resistant strains of S. typhimurium isolated from men and cattle in Germany.