Continuous Feeding of Antimicrobial Growth Promoters to Commercial Swine during the Grow/finishing Phase does not Modify Fecal Community Erythromycin Resistance or Community Structure

March 16, 2011 — 

Aims: To investigate the effect of continuous feeding of antimicrobial growth promoters (tylosin or virginiamycin) on the swine fecal community. Methods and Results: The study consisted of two separate on farm feeding trials. Swine were fed rations containing tylosin (44 or 88 mg/Kg of feed) or virginiamycin (11 or 22 mg/Kg of feed) continuously over the grow/finishing phases. The temporal impact of continuous antimicrobial feeding on the fecal community was assessed and compared to non-dosed control animals through anaerobic cultivation, the analysis of community 16S rRNA gene libraries and fecal volatile fatty acid content. Feeding either antimicrobial had no detectable effect on the fecal community. Conclusions: Erythromycin methylase genes encoding resistance to the macrolide-lincosamide-streptogramin B (MLS(B) ) antimicrobials are present at a high level within the fecal community of intensively raised swine. Continuous antimicrobial feeding over the entire grow/finishing phase had no effect on community erm-methylase gene copy numbers or fecal community structure. Significance and Impact of the Study: Antimicrobial growth promoters are believed to function by altering gut bacterial communities. However, widespread MLS(B) resistance within the fecal community of intensively raised swine likely negates any potential effects that these antimicrobials might have on altering the fecal community. These findings suggest that if AGP-mediated alterations to gut communities are an important mechanism for growth promotion, it is unlikely that these would be associated with the colonic community.

Kalmokoff M, Waddington LM, Thomas M, Liang KL, Ma C, Topp E, Dandurand UD, Letellier A, Matias F, Brooks SP; Continuous feeding of antimicrobial growth promoters to commercial swine during the grow/finishing phase does not modify fecal community erythromycin resistance or community structure; J Appl Microbiol. 2011 Mar 12. doi: 10.1111/j.1365-2672.2011.04992.x. [Epub ahead of print]