Phylogenetic association of fluoroquinolone and cephalosporin resistance of D-O1-ST648 Escherichia coli carrying blaCMY-2 from faecal samples of dogs in Japan.

This study aimed to investigate the genetic association between fluoroquinolone (FQ) and/or cephalosporin (CEP) resistance in Escherichia coli isolates from dogs, and the risk to human health. We characterized E. coli clinical isolates, derived from faecal samples of dogs attending veterinary hospitals, using phylogenetic grouping, determination of virulence factor (VF) prevalence, multilocus sequence typing (MLST) and O serotyping. The D group was the dominant phylogenetic group among strains resistant to FQ and/or CEP. In contrast, the dominant group among susceptible strains was group B2. Group D strains showed a significantly higher prevalence of VFs than strains belonging to groups A and B1, and were resistant to significantly more antimicrobials than group B2 strains. The phylogenetic distribution of FQ-CEP-resistant E. coli groups (FQ-CEPRECs) and FQ-resistant groups was significantly correlated (r = 0.98), but FQ-CEPRECs and CEP-resistant E. coli groups were not correlated (r = 0.58). Data from PFGE, O serotype and MLST analyses indicated that the majority of FQ-resistant strains derived from a particular lineage of phylogenetic group D: serotype O1 and sequence type (ST) 648. Some D-O1-ST648 strains carried blaCMY-2, showed multidrug resistance and possessed a higher prevalence of the VFs kspMT, ompT and PAI compared with other group D strains. Our data indicate that the emergence of FQ-CEP-resistant E. coli is based primarily on FQ-resistant E. coli. Moreover, as strains of the D-O1-ST648 lineage have been found in clinical isolates derived from humans at a relatively high frequency, our findings indicate that the spreading of D-O1-ST648 strains may cause serious difficulties in both veterinary and human clinical fields in the future.