Ciprofloxacin and nalidixic acid resistance of Salmonella spp. isolated from retail food in Poland

Abstract Distribution of amino acid substitutions in the quinolone resistance-determining region (QRDR) of gyrA , gyrB , parC , parE and determinants of plasmid-mediated quinolone resistance (PMQR) were investigated among quinolone-resistant Salmonella spp. strains isolated from retail food in Poland in the years 2008–2013. Ten different amino acid substitutions were identified in QRDRs. Five different amino acid substitutions were identified in gyrA : Ser83Tyr, Ser83Phe, Asp87Tyr, Asp87Asn, Asp87Gly, two amino acid substitutions in parC : Thr57Ser, Ser80Ile and in parE : Leu445Phe, Arg511Ser. One substitution — Ser464Phe — was detected within gyrB . In gyrA a single substitution (Ser83Tyr) was identified the most frequently – 34.8% (63/181). Second most frequently identified variant (21.0%–38/181) was a co-existence of two single substitutions in gyrA : Ser83Tyr and parC : Thr57Ser. In four isolates co-existed three substitutions in three different genes: gyrA : Ser83Tyr +  parC : Thr57Ser +  parE : Leu445Phe (two isolates), gyrA : Ser83Phe +  parC : Thr57Ser +  parE : Leu445Phe, and gyrA : Ser83Tyr +  parC : Thr57Ser +  parE : Arg511Ser. In the two isolates four substitutions were identified – in gyrA : Ser83Phe + Asp87Tyr and in parC : Thr57Ser + Ser80Ile. Among resistant isolates, MIC values varied between 32 and 2048 mg/L (nalidixic acid) and between 0.125 and 16 mg/L (ciprofloxacin). MIC values of two isolates harboring qnrS 1without any substitutions were 32 mg/L (NA) and 0.5–1.0 mg/L (CIP). The highest MIC values for NA and CIP were observed in two isolates of Salmonella spp. carrying double substitutions in gyrA : Ser83Phe + Asp87Tyr and parC : Thr57Ser + Ser80Ile. MIC value for NA was 2048 mg/L while for CIP – 16 mg/L.