Salmonella enterotoxin, Stn, regulates membrane composition and integrity

Abstract

Summary The mechanism of action of Salmonella enterotoxin (Stn) as a virulence factor in disease is controversial. Studies of Stn have indicated both positive and negative effects on Salmoenlla virulence. In this study, we attempted to evaluate Stn function and its effects on Salmonella virulence. To investigate Stn function, we first performed in vitro and in vivo analysis using mammalian cells and a murine ileal loop model. In these systems, we did not observe differences in virulence phenotypes between wild-type Salmonella and an stn gene-deleted mutant. We next characterized the phenotypes and molecular properties of the mutant strain under various in vitro conditions. The proteomic profile of total Salmonella cell membranes was remarkable for the absence of a protein in the mutant strain, which was identified as OmpA. By Far-Western blotting, OmpA interacted directly with Stn. To verify this result, the morphology of Salmonella was examined by transmission electron microscopy, with OmpA localized by immuno-gold labeling compared to wild-type Salmonella, the mutant strain had a different pole structure and a thin periplasminc space; OmpA was not seen in the mutant. These results indicate that Stn, via regulation of OmpA membrane localization, functions in the maintenance of membrane composition and integrity.