Genotypic and phenotypic characterization of enteric bacteria in an integrated population of swine and humans

Abstract

In two longitudinal studies, we examined the transmission dynamics of antimicrobial resistance (AMR) in an integrated, semi-closed population of humans and swine. A total of 1594 human and 1508 swine Escherichia coli (EC) and Enterococcus faecalis (EF) isolated from human wastewater and swine fecal samples were tested for antimicrobial susceptibility, for the presence of Class I integrons and gene cassettes that encode for AMR, and for the prevalence of van- comycin-resistant Enterococcus faecium (VRE). We showed that swine EC and EF had a higher prevalence of AMR than human isolates and that both swine and human EC had a low prevalence of Class I integrons. We isolated a total of 50 VRE from human wastewater samples and no VRE from swine samples. We concluded there was no apparent transfer of AMR from swine to human or vice versa, and that VRE may be more prevalent in the environment than previously thought. Introduction It is generally perceived by the medical community that antimicrobial resistance (AMR) in human infections is a consequence of sub-therapeutic antibiotic usage in animal produc- tion (Anderson, 1999). Because no definitive studies have determined this phenomenon, con- trolled epidemiologic studies with stable human and animal populations are needed to identify the transmission dynamics of AMR (Khachatourians, 1998). Scott et al., (2005) conducted a cross-sec- tional study in a uniquely integrated population of humans and swine to begin to address this need. Preliminary results suggested that occupational exposure of humans to swine did not appear to be associated with the prevalence of AMR in commensal fecal Escherichia coli (EC). The current study is a longitudinal continuation of the previous study in the same population (Scott et al., 2005). The objective of this study was to generate data over a two year period on the AMR phenotypic and genotypic profiles and potential AMR transmission dynamics of EC, Enterococcus faecalis (EF), and E. faecium in a semi-closed population of swine and humans.