title: Use of a Salmonella typhimurium hilA fusion strain to assess effects of environmental fresh water sources on virulence gene expression.
abstract: Many fruits and vegetables are irrigated with water from rivers, lakes and even wastewater systems. Irrigation may be a route for the introduction of Salmonella. Our objectives in this study were to determine survivability and virulence expression in a strain of Salmonella typhimurium when exposed to environmental water sources. Virulence expression was measured using a beta-galactosidase assay on a hilA:lacZY fusion strain of S. typhimurium. Water samples for environmental impact studies were taken from a local pond and specific sites along the Rio Grande River, which serves as a source of irrigation water in southern Texas. There was a significant difference (p<0.05) of virulence expression among the water sites. Certain regions along the Rio Grande River yielded greater amounts of beta-galactosidase activity than others. All sites yielded at least a two-fold greater virulence response than S. typhimurium grown in brain heart infusion. Salmonella survivors were enumerated as colony forming units (CFU)/ml as plated on a selective medium for the duration of 1 week and beta-galactosidase assays were performed to determine a possible correlation between culturable cells and virulence gene expression. Bacterial cells remained viable but decreased after 7 days incubation. In conclusion, water sampled at specific locations and at different times water samples exhibited differences in virulence expression in S. typhimurium.
authors.affiliation: Poultry Science Deptartment, Texas A and M University, MS 2472 TAMU, College Station, TX 77843, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Nutt
authors.forename: S D
authors.initials: SD
authors.lastname: Pillai
authors.forename: C L
authors.initials: CL
authors.lastname: Woodward
authors.forename: K L
authors.initials: KL
authors.lastname: Sternes
authors.forename: I B
authors.initials: IB
authors.lastname: Zabala-Díaz
authors.forename: Y M
authors.initials: YM
authors.lastname: Kwon
authors.forename: S C
authors.initials: SC
authors.lastname: Ricke
mesh_terms: D000383:Agriculture; D001426:Bacterial Proteins / Q000096:biosynthesis; D001681:Biological Assay; D004269:DNA, Bacterial / Q000032:analysis; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D005506:Food Contamination; D005638:Fruit; D015964:Gene Expression Regulation, Bacterial; D012486:Salmonella typhimurium / Q000235:genetics* / Q000472:pathogenicity*; D016019:Survival Analysis; D015534:Trans-Activators / Q000096:biosynthesis; D014675:Vegetables; D014774:Virulence; D014881:Water Supply; D001616:beta-Galactosidase
chemical_list: D001426:Bacterial Proteins; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; C102236:HilA protein, Salmonella; D015534:Trans-Activators; D001616:beta-Galactosidase