Selection of recombinant antibodies against Lawsonia intracellularis

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 vancomycin-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 production (Anderson, 1999). Because no definitive studies have determined this phenomenon, controlled 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-sectional 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. Materials and Methods Study Population The study design has been described (Scott et al., 2005; Campbell et al., 2005; Poole et al., 2005). The study population was composed of humans and swine in a semi-closed vertically integrated food system distributed over widely diverse geographical locations. There was moderate movement of humans into the system, but little movement out of the system. There was very little movement of swine (purebred breeding stock) into the system and no movement of swine out of the system. For the first year, the human population sampled was 21,000 and the swine sampled averaged about 45,000. During the second year, the representative human population was 39,000, whereas the swine population numbered 52,000. Bacteriology In the second year of the study, 987 human wastewater and 931composite swine fecal samples were cultured for the presence of commensal EC by use of CHROMagar-E. coli (DRG International, Mountainside, NJ) agar and confirmed as EC by API 20 test kits (API, bioMerieux, Hazelwood, NJ). Swine and human samples were streaked onto m-Enterococcus agar (Becton Dickinson, Sparks, MD) for EF isolations. API test kits were employed for species identification. Swine and human samples were also streaked onto M-Enterococcus agar that contained 20 μg vancomycin to screen for the presence of vancomycin-resistant E. faecium (VRE). Suspect VRE were verified by use of API test kits and PCR. Antibiotic Sensitivity Testing Minimum inhibitory concentrations of 16 and 19 antibiotics were determined by use of a micro-broth test kit (SensititreTM, Trek, Inc., Cleveland, OH) that employed antibiotic panels from the National Antimicrobial Resistance Monitoring System (NARMS). Susceptibility testing was performed on 829 human and 857 swine EC, and 345 human and 279 swine EF isolates from the second year sampling. EC isolates from the first year samples were pre-