Host-specific patterns of genetic diversity among IncI1-Iγ and IncK plasmids encoding CMY-2 β-lactamase in Escherichia coli isolates from humans, poultry meat, poultry and dogs in Denmark

CMY-2 is the most common plasmid-mediated AmpC β-lactamase in Escherichia coli isolates of human and animal origin. The aim of this study was to elucidate the epidemiology of CMY-2-producing E. coli in Denmark. Strain and plasmid relatedness was studied in 93 CMY-2-producing clinical and commensal E. coli isolates collected in 2006-2012 from humans, retail poultry meat, broilers and dogs. MLST, antimicrobial susceptibility testing and conjugation were performed in conjunction with plasmid replicon typing, pMLST, RFLP, and sequencing of selected blaCMY-2-harboring plasmids. MLST revealed high strain diversity with few E. coli lineages occurring in multiple host species and sample types. blaCMY-2 was detected on plasmids in 83 (89%) isolates. Most (75%) of these plasmids were conjugative and did not (96%) co-transfer resistance to other antimicrobials than cephalosporins. The main replicon types identified were IncI1-Iγ (55%) and IncK (39%). Isolates from different host species mainly carried distinct plasmid subtypes. Seven of the 18 human isolates harbored IncI1-Iγ/ST2, IncI1-Iγ/ST12 or IncK plasmids highly similar to those found among animal isolates, even though highly related human and animal plasmids differed by non-synonymous SNPs or insertion sequence elements. This study clearly demonstrates that the epidemiology of CMY-2 can only be understood by thorough plasmid characterization. To date the spread of this β-lactam resistance determinant in Denmark is mainly associated with IncK and IncI1-Iγ plasmids that are generally distributed according to host-specific patterns. These baseline data will be useful to assess the consequences of the increasing human exposure to CMY-2-producing E. coli via animal sources.

IMPORTANCE: CMY-2 is the most common plasmid-mediated AmpC β-lactamase in Escherichia coli This β-lactamase is poorly inhibited by clavulanic acid and confers resistance to cephamycins, third-generation cephalosporins and aztreonam. Further, resistance to carbapenems has been reported in E. coli as a result of production of plasmid-encoded CMY-2 β-lactamase in combination with decreased outer membrane permeability. The gene encoding CMY-2 generally resides on transferable plasmids belonging to different incompatibility groups. The prevalence of CMY-2-mediated cephalosporin resistance in E. coli varies significantly depending on geographical region and host. This study demonstrates that the epidemiology of CMY-2 can only be understood by thorough plasmid characterization. To date the spread of this β-lactam resistance determinant in Denmark is mainly associated with IncK and IncI1-Iγ plasmids that are generally distributed according to host-specific patterns. These data will be useful to assess the consequences of the increasing human exposure to CMY-2-producing E. coli via animal sources.