#05-198

Complete

Date Full Report Received

02/28/2007

Date Abstract Report Received

09/09/2008

Investigation

Institution: , ,
Primary Investigator:
Co-Investigators: Nicole Ramlachan

A series of laboratory experiments were conducted to assess the effects of low (25 ug/ml) or high (100 ug/ml) tylosin treatment on potential development, amplification, persistance and transfer of tylosin resistance within a mixed population of gut bacteria derived from gut contents of a feral or a domestic pig. Results showed that tylosin-resistant bacteria such as Clostridium and Bacteroides, were differentially prominant in the mixed bacterial populations from the pigs, with tylosin-resistant Clostridium being recovered from the feral pig and the tylosin-resistant Bacteroides being recovered from the domestically reared pig. Results further showed that under the experimental conditions used here, these populations could certainly be amplified or increased more easily by administering a low rather than a high level of tylosin and that resistant populations amplified in mixed populations from the feral pig did not persist as long as those from the domestic pig. Results also demonstrated that tylosin-insensitive Enterococcus spp., while initially absent or at very low concentrations from both of the mixed populations, were enriched and amplified in the population from the domestic pig but not from the feral pig. Experimental infection of the populations with a known tylosin-resistant Enterococcus faecium bacterium provided evidence that at 100 µg tylosin/ml, genetic transfer occurred between this challenge organism and the naturally present Enterococcus spp. in the mixed populations, as the resistance gene, known as ermB, was found in the naturally present Enterococcus after they had acquired resistance but not before. These results will help antibiotic users to appropriately manage all antibiotics at their disposal and ultimately will help provide farmers, scientists and U.S. public health officials with important information to make sound, science-based decisions for the good of public health and animal production.