Incidence of quinolone resistance in strains of Salmonella isolated from poultry, cattle and pigs in Germany between 1998 and 2001

This paper reports the susceptibility to the quinolone nalidixic acid and the fluoroquinolone ciprofloxacin of 14,514 strains of Salmonella isolated in Germany from poultry, cattle and pigs between 1998 and 2001. Quinolone-resistant salmonellae were most frequently isolated from poultry, with a prevalence of 10.2 to 16.8 per cent. Poultry-associated serotypes, such as Salmonella Paratyphi B (d-tartrate positive), Salmonella Hadar and Salmonella Virchow, had the highest prevalence of quinolone resistance, ranging between 35 and 74 per cent. All the nalidixic acid-resistant strains also had a reduced susceptibility to ciprofloxacin, with minimum inhibitory concentrations (MICs) of 0.125 to 2 mug/ml. A comparison of the mics for ciprofloxacin of the strains of these poultry-associated serotypes and Salmonella Enteritidis phage type 4 isolated in 1998/99 and 2000/01 indicated that there had been a shift towards higher mic values of up to 2 mug/ml. The quinolone resistance-determining region (QRDR) of the gyrA gene and the homologue region of the parC gene of 31 selected strains were sequenced. Several different amino acid changes were observed in gyrA of the quinolone-resistant isolates at positions 83 and 87, but no substitutions were observed in parC.