Submitted to: Australasian Pig Science Association Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 8/15/2005
Publication Date: 11/27/2005
Citation: Harvey, R.B., Scott, H.M., Alali, W.Q., Highfield, L.D., Anderson, R.C., Nisbet, D.J. 2005. Antimicrobial resistance of Escherichia coli and Enterococcus spp. from an integrated, semi-closed population of humans and swine [abstract]. Proceedings of Australasian Pig Science Association Biennial Conference. p. 25.
Technical Abstract: It is perceived by some in the medical community that antimicrobial resistance (AMR) in human infections is a consequence of sub-therapeutic antibiotic usage in animal production. Because no definitive studies have determined this, controlled epidemiologic studies with stable human and animal populations are needed to identify the transmission dynamics of AMR. The objective of this study was to generate data on the AMR profiles and potential transmission dynamics of Escherichia coli (EC), Enterococcus faecalis (EF), and E. faecium in a semi-closed population of swine and humans. The study population consisted of humans (21,000 swine and non-swine workers) and swine (45,000) in a multi-site, vertically integrated swine operation. There was little to moderate movement of humans into the system and little movement out of the system, whereas there was very little swine movement into the system and no movement out of the system. Composite swine fecal samples and human wastewater samples were collected monthly from January to December 2004. There were 987 human wastewater and 931 swine fecal samples cultured for EC and EF. EC were isolated from 84% of the human samples while 35% were positive for EF. Antibiotic sensitivity was tested by use of a micro-broth dilution (Sensititre®) system and Gram-negative (CMV1AG-NF) and Gram-positive (CMV1AG-PF) panels from the National Antimicrobial Resistance Monitoring System (NARMS). Fifty-three percent of the human EC isolates were pan susceptible, 26% were singly resistant, and 21% were resistant to 2 or more antimicrobials. Of the human EF, 3% were pan susceptible, 9% were singly resistant, and 88% were resistant to 2 or more antimicrobials. EC were isolated from 92% of swine samples whereas 30% were positive for EF. Of the EC, 12% were pan susceptible, 37% were singly resistant, and 51% were resistant to 2 or more antimicrobials. None of the swine EF were pan susceptible, 1% were singly resistant, and 99% were multi-resistant. During this study, 17 vancomycin-resistant E. faecium (VRE) were isolated from human wastewater from multiple geographic locations. No VRE were isolated from swine samples. These are believed to be the first non-clinical isolations of VRE in the U.S. Our preliminary results suggest that swine EC and EF have increased AMR compared to human isolates, that there was no apparent AMR transfer from swine to humans or vice versa, and that VRE may be more common in the environment than previously perceived. Longitudinal studies in this population will continue until 2007, and AMR will be further characterized by use of PCR and real-time PCR to detect the presence of genetic factors such as integrons, plasmids, and gene cassettes that encode for AMR.