Characterization of multidrug-resistant Enterobacteriaceae carrying plasmid-mediated quinolone resistance mechanisms in Spain

The aim of this study was to detect and characterize plasmid-mediated quinolone resistance determinants as well as genes responsible for additional resistances in Enterobacteriaceae isolates in Spain. The resistance genes were identified by PCR and sequencing. Plasmid analysis was carried out by S1-PFGE and PCR-based replicon typing. Conjugation assays were performed to link resistance genes to plasmids. The genetic relationships among the strains were determined by XbaI-PFGE. One hundred and twenty-three isolates carried qnr as the only quinolone resistance determinant. One Salmonella Bredeney was positive for qnrB2 harboured on a 320 kb conjugative IncHI2 plasmid. One Salmonella Newport was positive for qnrB4 harboured on a 70 kb conjugative IncFIIs plasmid. Twenty-five Salmonella Thompson were positive for qnrA1. Twenty-two harboured a 220 kb non-conjugative and non-typeable plasmid, two a 220 kb conjugative IncHI2 plasmid and one a 120 kb non-conjugative IncA/C plasmid. qnrS1 was always detected on non-conjugative ColE(TP) plasmids of various sizes. Thus, two Salmonella Montevideo strains carried a 20 kb plasmid while Salmonella Typhimurium strains carried plasmids of 10 kb (n = 91) or 30 kb (n = 2). One Escherichia coli was positive for qnrA1 detected on a 220 kb conjugative IncHI2 plasmid. qnr alleles and beta-lactamases were associated in Salmonella Bredeney (harbouring bla(SHV-12)), Salmonella Newport (harbouring bla(DHA-1)) and E. coli (harbouring bla(CTX-M-9)). This is the first epidemiological study of qnr genes in Enterobacteriaceae isolates from Spain. Salmonella plasmids bearing qnr alleles are not a localized phenomenon in Spain and wide variation in plasmids and co-resistance was detected. The presence of qnr determinants in Salmonella serotypes commonly reported in human disease is concerning.