Impacts of a Poultry Processing Plant on the Diversity of Escherichia coli Populations and Transferability of Tetracycline Resistance Genes in an Urban Stream in South Carolina

Anderson, Brent W.; McCauley, Steve; Lewis, Gregory P.; Liao, Min-Ken

Impacts of a Poultry Processing Plant on the Diversity of Escherichia coli Populations and Transferability of Tetracycline Resistance Genes in an Urban Stream in South Carolina

2014

Anderson, Brent W. | McCauley, Steve | Lewis, Gregory P. | Liao, Min-Ken

Poultry feed is often supplemented with low dosages of antibiotic to promote growth, making farms and animal processing facilities potential point sources of antibiotic-resistant fecal bacteria to aquatic ecosystems. In 2010 and 2011, we detected high concentrations of fecal indicator bacteria (FIB) in effluent released from a poultry processing plant into a headwater stream in Greenville, South Carolina. The FIB pollution became undetectable in 2012 with the plant under new management. To determine the plant’s impacts on the stream, we compared the genetic variations of Escherichia coli populations from upstream and downstream of the plant and from reference streams in the same watershed by classifying each isolate into an E. coli reference collection (ECOR) phylogenetic group. For tetracycline-resistant E. coli isolates, we analyzed the resistance genes, minimum inhibitory concentrations (MICs), gene transferability, and plasmid incompatibility groups (Inc). Distributions of ECOR groups upstream and downstream of the plant differed significantly in 2011 but not in 2012. The resistance genes tet(A) and tet(B) were prevalent, with tet(A) more likely to be found on the promiscuous IncP plasmid. A higher percentage of isolates having both tet(A) and tet(B) was found downstream in 2011 than in 2012. Dual-gene isolates did not have higher MICs than single-gene isolates but were more likely to transfer tet(A) on IncP. We propose that the processing plant acted not only as a point source of FIB but also as a factor influencing gene transferability. Additionally, given the results from 2012, the FIB impacts of the processing plant appeared to be reversible.

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