Diversity, Virulence, and Clinical Significance of Extended-Spectrum β-Lactamase- and pAmpC-Producing Escherichia coli From Companion Animals

Abstract

<i>Escherichia coli</i> are opportunistic pathogens with the potential to cause a variety of infections in both humans and animals and in many cases have developed antimicrobial resistance. In this study, we characterized extended-spectrum cephalosporin resistant (ESCR) <i>E. coli</i> isolates from diseased companion animals (dogs, cats, and horses) and related the results to clinical findings. ESCR <i>E. coli</i> clinical isolates obtained over a 6-year period were screened for extended-spectrum β-lactamase (ESBL) and/or plasmid mediated AmpC (pAmpC) and virulence markers likely to be associated with extraintestinal pathogenic <i>E. coli</i> (ExPEC). ESBL and/or pAmpC genetic determinants were identified in 79.9% of the ESCR <i>E. coli</i> isolates with <i>bla</i> _CTX-M genes being the most common ESBL genotype of which <i>bla</i> _CTX-M-15, <i>bla</i> _CTX-M-14, and <i>bla</i> _CTX-M-55 were the most prevalent. In addition, <i>bla</i> _{CMY -2} was the most common genotype identified amongst pAmpC producing isolates. Phylogenetic group typing showed that B2 was the most prevalent phylogroup among the ESCR <i>E. coli</i> isolates, followed by the closely related phylogroups D and F which are also associated with extra-intestinal infections. ESCR was also identified in phylogroups commonly regarded as commensals (B1, A, and C). Virulence factor (VF) scores >2 were mostly present amongst isolates in phylogroup B2. Higher virulence scores were found in isolates lacking ESBL/pAmpC resistance genes compared with those carrying both genes (<i>p</i> < 0.05). Five of phylogroup B2 isolates, were typed to the pandemic virulent O25b-ST131 clone and three ST131 isolates carrying <i>bla</i> _CTX-M-15 belonged to the subclade C2/H30Rx whilst one isolate carrying <i>bla</i> _CTX-M-27 typed to the recently described sub-clade C1-M27. MLST typing also identified other sequence types commonly associated with infections in humans (ST410, ST10, and ST648). Most ESCR <i>E. coli</i> isolates obtained in pure growth were cultured from normally sterile body sites (mostly from urinary tract infections, UTIs) whilst only a small proportion were obtained from body sites populated with commensal flora (<i>p</i> < 0.0001). Our study has shown that ExPEC ESBL/pAmpC producing <i>E. coli</i> isolates are common amongst companion animal isolates and are associated with colonization and infection. In addition, their isolation from a normally sterile site is likely to be clinically significant and warrants antimicrobial treatment.