The present study was aimed at determining the effects of supplemental feed grade antimicrobials on the selection and co-selection of copper resistance among enteric bacteria in post-weaning pigs. In our earlier studies, we showed that increased supplementation of copper selects for copper resistance among fecal Enterococcus spp. of piglets in the US and also co-selects for tetracycline and erythromycin traits co-located on the same genetic element (a very large plasmid). This represents a threat to the US animal agriculture since several of these bacteria have a high propensity for transferring their resistance determinants to other enteric bacterial flora (both commensal and pathogenic bacteria). To further these findings, we included in our present study both feed grade tylosin and chlortetracycline (commonly used antibiotics during the post-nursery stage) alone and also in combination with copper as per NRC guidelines. The study was conducted in a segregated early weaning facility consisting of two separate barns of 40 pens each.
Our study demonstrated that the supplementation of antibiotics in combination with copper does increase the prevalence of copper resistant enterococci when compared to feeding copper or antibiotics by themselves. All copper-resistant enterococcal isolates were also phenotypically and genotypically resistant to erythromycin and tetracycline (though the reverse was not always the case). It remains unclear at this time as to which practices producers should pursue to minimize selection for copper resistance among enterococci in commercial production settings. However, given the extremely rare presence of vancomycin resistant enterococci in U.S. swine production, it seems unlikely that co-selection of such resistance by copper, tylosin, or chlortetracycline will occur in the near future.
For more information please contact:
Dr. H. Morgan Scott
Professor, Epidemiology
E. J. Frick Professor of Veterinary Medicine
Department of Diagnostic Medicine/Pathobiology
332 Coles Hall, 1800 Denison Avenue
College of Veterinary Medicine, Kansas State University
Manhattan, Kansas, USA 66506-5705
Email: [email protected].
