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

Distribution of aminoacid substitutions in the quinolone resistance-determining region (QRDRs) of gyrA, gyrB, parC, parE and determinants of plasmid-mediated quinolone resistance (PMQR) were investigated among resistant to quinolones Salmonella spp. strains isolated from retail food in Poland in years 2008-2013. Ten different aminoacid substitutions were identified in QRDRs. Five different aminoacid substitutions were identified in gyrA: Ser83Tyr, Ser83Phe, Asp87Tyr, Asp87Asn, Asp87Gly, two aminoacid substitutions both in parC: Thr57Ser, Ser80Ile and in parE: Leu445Phe, Arg511Ser. One substitution - Ser464Phe - was detected within gyrB. Single substitution in gyrA (Ser83Tyr) were identified the most frequently – 34.8% (63/181). Second, the most frequently identified variant (21.0% - 38/181) were 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, gyrA: Ser83Tyr + parC: Thr57Ser + parE: Arg511Ser. In two isolates, four substitutions were identified - in gyrA: Ser83Phe + Asp87Tyr and in parC: Thr57Ser + Ser80Ile. Among resistant isiolates, MIC values varied between 32 and 2048 mg/L (nalidixic acid) and between 0,125 – 16 mg/L (ciprofloxacin). MIC values of two isolates harboring qnrS1without 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.