ARS | Publication request: The swine gastrointestinal tract and stored manure: reservoirs of antibiotic resistance?

Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: May 27, 2010
Publication Date: May 27, 2010
Citation: Whitehead, T.R., Cotta, M.A. 2010. The swine gastrointestinal tract and stored manure: reservoirs of antibiotic resistance?. American Society for Microbiology. Paper No. Z-978.

Technical Abstract: Antimicrobial compounds have been commonly used as feed additives for domestic animals to reduce infection and promote growth. Recent concerns have suggested such feeding practices may result in increased microbial resistance to antibiotics, which can have an impact on human health. While many investigations have centered on antibiotic resistance in coliforms and other aerobic bacteria, less attention has been directed towards investigating antibiotic resistance in the commensal microflora found in the feces and stored manure of domestic animals. These ecosystems may serve as reservoirs of antibiotic resistance genes. Our laboratory has been studying the predominant commensal bacterial populations present in both pig feces and manure storage pits in relation to odor production from swine facilities. Results of pure culture isolation and direct 16S rDNA sequence analyses indicate that the bacterial populations of both ecosystems are predominantly composed of anaerobic, low mol% G+C, Gram-positive bacteria, most of which represent novel genera and species. As part of this study, we investigated the potential antibiotic resistance in the commensal bacterial populations. Pure cultures were isolated following plating on anaerobic media containing tetracycline, tylosin, or erythromycin. Polymerase chain reaction (PCR) analyses using primers based on a variety of antibiotic resistance genes was carried out with both pure culture isolates and total deoxyribonucleic acid (DNA) from swine feces and stored manure. Results of these studies demonstrated the presence of a variety of tet (e.g., tetK, tetO) and erm (e.g., ermA, ermC, ermG) resistance gene classes in both pure cultures and total DNA, and the identification of novel bacteria containing new resistance genes. Comparison of DNA sequences suggests that horizontal transfer of resistance genes between bacterial strains has also occurred. The data indicate that both the swine gastrointestinal (GI) tract and stored swine manure may serve as reservoirs of known and novel antibiotic resistant bacteria and resistance genes.