SALMONELLA-ENTERITIDIS HAS A HOMOLOG OF TOLC THAT IS REQUIRED FOR VIRULENCE IN BALB C MICE/

The ability of Salmonella to invade tissue culture cells is correlated with virulence. Therefore, the tissue culture invasion model has been used extensively to study this process and to identify the bacterial genes involved and their products, Described here is the further chara cterization of a Salmonella enteritidis mutant (SM6T) originally ident ified as non-invasive for tissue culture cells. A chromosomal DNA frag ment complementing this defect was cloned and sequenced. The derived p rotein sequence is 89% identical to TolC from Escherichia coli, an out er membrane protein required for the signal peptide-independent transp ort of alpha-haemolysin and colicin V. Therefore, sinA was renamed tol C and is referred to in this text as tolC(s) to distinguish it from to lC of E. coli. TolC(s) and TolC are functionally similar since tolC ca n complement the invasion-defective phenotype of a tolC(s) mutant, and tolC(s) is required for export of alpha-haemolysin by Salmonella. The tolC(s) mutant is avirulent for mice when administered by the oral ro ute, suggesting that the gene is important for virulence, Further char acterization of the tolC(s) mutant indicated that like tolC mutants it is more sensitive than the wild-type strain to various detergents, an tibiotics and dyes. This mutant is more sensitive to Triton X-100 only when associated with the monolayer, and the invasion defective phenot ype appears to be an artifact of this sensitivity. In addition, the to lC(s) mutant is more sensitive to the bactericidal activity of human s erum, Therefore, the avirulent phenotype could be the result of an ina bility to secrete a necessary virulence factor, or an increased sensit ivity to complement and detergents as a result of a subtle alteration in the lipopolysaccharide (LPS) associated with tolC mutations.