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 United States and also co-selects for tetracycline and erythromycin traits. This represents a threat to U.S. animal agriculture since several of these bacteria have a high propensity for transferring their resistance determinants to other enteric bacterial flora. This new study found that the supplementation of antibiotics in combination with copper does increase the prevalence of copper-resistant enterococci when compared to feeding copper or antibiotics alone. 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.
Key Points:
- Feed-grade antibiotics and copper supplements can both help create resistant bacteria in postweaned pigs.
- Feeding antibiotics combined with copper increases the selection for copper-resistant bacteria.
- On-farm measures to reduce potential resistance remain unclear, but odds of public health impact remain extremely small.
Principal Investigator: H. Morgan Scott, Kansas State University
Source: Pork Checkoff Research Review – September-October 2012