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 p lasmid-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 p efC was found to be associated in lower numbers with marine small inte stine than the wild type. Similarly, heterologous expression of PE fim briae in Escherichia coli increased the bacterial numbers recovered fr om the intestine in the organ culture model, Adhesion to villous intes tine 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 accumul ation was investigated in infant mice, Intragastric injection of S. ty phimurium 14028 and SR-11 caused fluid accumulation in infant mice, In contrast, pefC mutants of S. typhimurium 14028 and SR-11 were negativ e in the infant mouse assay, Introduction of a plasmid containing pefB ACD and orf5, the first five genes of the pef operon, into the pefC mu tant complemented for fluid accumulation in the infant mouse assay, Ho wever, heterologous expression of PE fimbriae in E. coli did not resul t in fluid accumulation in the infant mouse, suggesting that factors o ther than fimbriae are involved in causing fluid accumulation.