FITNESS AND PATHOGENICITY OF OUTBREAK CAUSING Salmonella UPON SHORT-TERM EXPOSURE TO GROUNDWATER WITH RESIDUAL ANTIBIOTICS

Abstract

The changes in survival and pathogenicity of three Salmonella enterica subsp. enterica serotypes upon short term exposure to groundwater with residual antibiotics have been studied in relationship to overall microbial fitness. A wild type flagellated Salmonella enterica ser. Typhimurium outbreak strain, a mutant Salmonella enterica ser. Typhimurium strain, and a wild type avian disease-causing Salmonella enterica ser. Pullorum strain were exposed to a range of ionic strength (3-30 mM) groundwater with residual antibiotics for 6-24 hours. Exposed organisms’ pathogenicity was tested in vitro exposure to a human epithelial cell line (HEp2). Resistance profiles against 10 common antibiotics were also tested and compared to unexposed controls. Results show minor antibiotic resistance changes for S. enterica ser. Typhimurium strains in response to some antibiotic classes mediated with active efflux pumps. This trend was not observed for S. enterica ser. Pullorum, suggesting that resistance found in groundwater exposed organisms might be strain-dependent. In vitro epithelial cell invasion assays showed bacterial invasion of HEp2 cells initially decreases with time and increases after 24 hours. It is concluded that S. enterica serotypes reaching groundwater environments in the presence of residual antibiotics may exhibit increased levels of pathogenicity, strain-dependent resistance to antibiotics, and sustained levels of viability.