Recovery of Virulent Salmonella from Sediment Samples Collected from the North River.

Pathogenesis of Salmonellosis depends upon a large number of factors controlled by an array of genes that synergize into the actual virulence of Salmonella. Survival and growth of Salmonella outside of host cells are important aspects of the potential environmental impacts of bacterial virulence. The distribution of four virulence genes, HilA, invA, spvC, and sirA in Salmonella isolates (n = 80) obtained from stream sediments were investigated by polymerase chain reaction (PCR). Sediment samples were collected from 8 locations along the North River in Carteret County, NC. The hilA gene encodes an OmpR/ToxR family transcriptional regulator that activates the expression of invasion genes in response to both environmental and genetic regulatory factors. The Salmonella invasion gene invA, is the first gene in an operon which is thought to trigger the internalization of S. typhimurium in cultured epithelial cells. The sirA gene which is known to regulate the hilA and hilC genes and also regulates horizontally acquired virulence genes. Finally the isolates were also evaluated for the spvC gene that is encoded by the Salmonella virulence plasmid. The Salmonella isolates were identified by conventional serotyping.  More than four serotypes were found and these serotypes may be good indicators of specific contamination sources. All (n =80) were positive for the invA gene sequence and less than 10% were positive for the spvC gene. Varying distribution patterns of sirA and hilA were observed among the isolates.  These findings indicate that virulent Salmonella persist in sediments and therefore their presence in environmental waters may be of epidemiological significance.