<i>Enterobacteriaceae</i> Harboring AmpC ( <i>bla</i> _CMY ) and ESBL ( <i>bla</i> _CTX-M ) in Migratory and Nonmigratory Wild Songbird Populations on Ohio Dairies

Abstract

Extended-spectrum β-lactamases (ESBLs) confer bacterial resistance to critically important antimicrobials, including extended-spectrum cephalosporins (ESCs). Livestock are important reservoirs for the zoonotic food-borne transmission of ESC-resistant enteric bacteria. Our aim is to describe the potential role of migratory and resident wild birds in the epidemiology of ESBL-mediated bacterial resistance on dairy farms. Using mist nets, we sampled wild migratory and resident birds either immediately adjacent to or 600 ft away from free-stall barns on three Ohio dairy farms during the 2014 and 2015 spring migrations. Individual swabs were used to obtain both a cloacal and external surface swab from each bird. Samples were inoculated into MacConkey broth containing cefotaxime then inoculated onto MacConkey agar with cefoxitin, cefepime, or meropenem to identify the bla_CMY, bla_CTX-M, and carbapenemase phenotypes, respectively. Six hundred twenty-three birds were sampled, 19 (3.0%) of which harbored bacteria with bla_CMY and 32 (5.1%) harbored bacteria with bla_CTX-M from either their cloacal sample or from their external swab. There was no difference in the prevalence of either gene between migratory and resident birds. Prevalence of bla_CMY and bla_CTX-M was higher among birds sampled immediately outside the barns compared with those sampled 600 ft away. Our results suggest that wild birds can serve as mechanical and/or biological vectors for Enterobacteriaceae with resistance to ESCs. Birds live in close contact with dairy cows and their feed, therefore, transmission locally between farms is possible. Finding a similar prevalence in migratory and nonmigratory birds suggests the potential for regional and intercontinental movement of these resistance genes via birds.