|Chee Sanford, Joanne|
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2001
Publication Date: N/A
Citation: Interpretive Summary: Low-level (subtherapeutic) concentrations of antibiotics are routinely administered in animal feed to promote growth and prevent disease. Growers commonly use lagoons to hold the large amount of animal waste generated, and there is concern over environmental contamination with antibiotic resistant bacteria due to lagoon seepage or leaks. Bacteria that contain a specific antibiotic resistance gene have the ability to resist that specific drug. Antibiotic resistance genes can potentially be transferred between bacteria, creating a chain for mobilizing resistance genes. In addition, residues of the drugs in the environment may also promote the acquisition of resistance genes in natural soil bacteria. These effects may have a direct impact on human and animal health, where there is heightened concern over the future impact on effective treatment for bacterial-borne diseases using antibiotics. In this study, we detected tetracycline resistance genes in groundwater located beneath two large swine farms. Tetracycline was routinely used at these farms and groundwater was used as the drinking water supply to one of the farms. The same tetracycline resistance genes were present in gastrointestinal bacteria and in natural soil bacteria. Significant findings in this study were 1) groundwater contamination occurred, 2) groundwater can mobilize the genes a large distance, and 3) animal agriculture can be a source of the contamination. Evaluations can be made on the possible link between subtherapeutic antibiotic use in animal agriculture and on increasing reservoir of resistance genes among bacteria. These data will contribute to our overall understanding of the ecology of antibiotic resistance genes.
Technical Abstract: In this study, we used PCR typing methods to assess the presence of tetracycline resistance determinants conferring ribosomal protection in waste lagoons and in groundwater underlying two swine farms. All eight classes of genes encoding this mechanism of resistance [tet(O), tet(Q), tet(W), tet(M), tetB(P), tet(S), tet(T), and otrA] were found in total DNA extracted from water of two lagoons. These determinants were found to be seeping into the underlying groundwater and could be detected as far as 250 m downstream from the lagoons. The identities and origin of these genes in groundwater were confirmed by PCR-denaturing gradient gel electrophoresis and sequence analyses. Tetracycline-resistant bacterial isolates from groundwater harbored the tet(M) gene, which was not predominant in the environmental samples and was identical to tet(M) from the lagoons. The presence of this gene is some typical soil inhabitants suggests that the vector of antibiotic resistance gene dissemination is not limited to strains of gastrointestinal origin carrying the gene but can be mobilized into the indigenous soil microbiota. This study demonstrated that tet genes occur in the environment as a direct result of agriculture and suggested that groundwater may be a potential source of antibiotic resistance in the food chain.