The pef fimbrial operon of Salmonella typhimurium mediates adhesion to murine small intestine and is necessary for fluid accumulation in the infant mouse

We investigated the role of the pef operon, containing the genes for plasmid-encoded (PE) fimbriae of Salmonella typhimurium, in adhesion to the murine small intestine. In an organ culture model, a mutant of S. typhimurium carrying a tetracycline resistance cassette inserted in pefC was found to be associated in lower numbers with murine small intestine than the wild-type. Similarly, heterologous expression of PE fimbriae in Escherichia coli increased the bacterial numbers recovered from the intestine in the organ culture model. Adhesion to villous intestine mediated by PE fimbriae was further demonstrated by binding of an E. coli strain expressing PE fimbriae to thin sections of mouse small intestine. The contribution of pef-mediated adhesion on fluid accumulation was investigated in infant mice. Intragastric injection of S. typhimurium 14028 and SR-11 caused fluid accumulation in infant mice. In contrast, pefC mutants of S. typhimurium 14028 and SR-11 were negative in the infant mouse assay. Introduction of a plasmid containing pefBACD and orf5, the first five genes of the pef operon, into the pefC mutant complemented for fluid accumulation in the infant mouse assay. However, heterologous expression of PE fimbriae in E. coli did not result in fluid accumulation in the infant mouse, suggesting that factors other than fimbriae are involved in causing fluid accumulation.