Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 6/26/2003
Publication Date: 6/26/2003
Citation: WHITEHEAD, T.R., COTTA, M.A., WHITTLE, G., SHOEMAKER, N., SALYERS, A.A. THE COMMENSAL BACTERIAL POPULATIONS OF SWINE FECES AND STORED SWINE MANURE: RESERVOIRS OF ANTIBIOTIC RESISTANCE?. JOURNAL OF ANIMAL SCIENCE. 2003. V. 81(SUPPL.1): ABSTRACT P. 461. Interpretive Summary:
Technical Abstract: In order to facilitate improved growth and reduce infection, a number of antimicrobial compounds are commonly added at subtherapeutic levels to the feed of domestic animals in the United States. This practice has come under intense scrutiny of late, as a number of recent reports have suggested that increased microbial resistance to the antibiotics may have an impact on human health. Most investigations have centered on antibiotic resistance in known pathogens and aerobic bacteria. However, the great majority of the bacteria present in the commensal microflora found in the feces and stored manure of domestic animals, including swine, are anaerobic bacteria. These normal residents may serve as natural reservoirs of antibiotic resistance genes. We have initiated an investigation of antibiotic resistant (AR) anaerobic bacteria present in both pig feces and manure storage pits. Samples were collected from a local swine facility where tylosin was used at subtherapeutic levels. AR anaerobic bacteria were enumerated on complex media with and without tetracycline (Tc), erythromycin (Em), or tylosin (Ty) at 10 ug/ml. AR bacteria were found in all samples, and the level of resistance ranged from 4% resistant to 32% resistant. Several Em/Ty resistant strains were also Tc resistant. Results of PCR and DNA sequencing analyses of pure cultures and total DNA from both ecosystems demonstrated the presence of various classes of erythromycin and tetracycline resistance genes, including the first reported identification of ermT in the United States. In addition, new classes of erythromycin (erm (35)) and tetracycline (tet (36)) resistance genes have been recently identified in the isolates. The tet (36) gene has been identified in Gram-positive and Gram-negative isolates, suggesting that the gene is being transferred between microorganisms. The finding of a high number of identified and unidentified AR eubacteria and gene classes in swine feces and manure storage pits suggests that these ecosystems may serve as reservoirs of antibiotic resistance genes. The influence of feeding antibiotics on the levels of AR resistance in these populations has yet to be ascertained.