Abstract: The invention provides a system for creating recombinant agfA fimbrin genes and performing chromosomal gene replacements within Salmonella, creating Salmonella strains which carry the recombinant agfA genes at the native position in the chromosome. One embodiment of the invention is exemplified by the expression of a model epitope (PT3) obtained from the GP63 protein of Leishmania major, by formation of recombinant agfA genes encoding PT3 fusion proteins recombined at 10 different sites throughout the agfA gene. These fusions are shown to be expressed in the thin aggregative fimbriae on the surface of bacterial cell. The agfA fimbrin of Salmonella (CsgA for E. coli) provides a flexible and stable vehicle for the expression of foreign epitopes in enterobacteriaceae and the subsequent thin aggregative fimbriae (curli) expression product provide an ideal organelle for presentation of the foreign epitopes at the cell surface.

Abstract: An isolated nucleic acid molecule comprising the agfA gene of Salmonella. Methods and compositions suitable for diagnostic tests utilizing the isolated gene, and protein therefrom, to give highly specific diagnostic assays to Salmonella, and/or enteropathogenic bacteria of the family Enterobacteriaceae.