Submitted to: Research Workers in Animal Diseases Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 9/30/2001
Publication Date: 11/11/2001
Citation: Kim, L.M., Cray, P.J., Gray, J.T., Jones, R. 2001. Antimicrobial resistance in e. coli from growing piglets fed diets with and without feed-based subtherapeutic antimicrobials. Research Workers in Animal Diseases Conference Proceedings. No. 73. Interpretive Summary:
Technical Abstract: The impact of feed-based subtherapeutic antimicrobial use in food animal production and its effect on antimicrobial drug resistance among enteric bacteria is not well understood. We evaluated the antimicrobial susceptibilities of fecal E. coli population from growing piglets fed diets with and without subtherapeutic apramycin (P1), carbadox (P2 and P3), and tetracycline (P4). Two replicate trials, 4 months apart, were performed for this study using different sows. Sows did not receive FSAs during gestation, farrowing, or post-farrowing. After farrowing, fecal samples were cultured regularly from sows and all piglets, and recovery of 12 E. coli isolates per animal was attempted. Antimicrobial susceptibility was tested using breakpoint MIC levels for tetracycline (16ug/ml), apramycin (34ug/ml), and gentamicin (16ug/ml). In total 16,329 isolates were analyzed (trial 1=7,7557, trial 2=8,772). Resistance to tetracycline was relatively high regardless of sample, group, or trial, with averages ranging between 65% and 90% of isolates. For the sows, there was an increase in apramycin resistance during farrowing. For piglets in both trails, resistance to apramycin was higher in pigs fed subtherapeutic apramycin (P1), with resistance declining during feeding of carbadox (P2 and P3). During feeding of tetracycline (P4), apramycin resistance remained unchanged in trial 1, but increased slightly in trial 2. In trial 1, gentamicin resistance paralleled apramycin resistance, however, in trial 2 gentamicin resistance remained at low levels. These results indicate that production use of FSAs can have complex effects on antimicrobial resistance of enteric bacteria, and further research is needed to understand this interaction.