Abstract: Compositions, methods and kits are provided for identifying at least one virulence factor of a Gram-negative bacterial strain, and for preparing attenuated bacterial strain vaccines or a modulator that selectively binds to or inhibits expression of the virulence factor. The Gram-negative bacterial strain is a short facultatively aerobic or micro-aerobic rod or an enteric strain including at least one pathogen selected from the group of: Salmonella, Escherichia, Yersinia, Klebsiella, Shigella, Enterobacter, Serratia, Pseudomonas, and Citrobacter. Novel genes encoding virulence factors are identified, so that non-virulent mutant strains are available for vaccine development.

Abstract: Novel methods and microorganisms are provided, where novel genetic mammalian cell invasive capability is imparted to a microorganism by the introduction of an exogenous inv gene. The resulting organisms are then capable of binding to mammalian cells and are transferred to the cytoplasm. Other novel genetic capabilities may be imparted to the unicellular microorganism, which may serve as a vaccine for one or more pathogens or may introduce genetic capabilities or foreign molecules into a mammalian host cell. The sequences may be used for an in vitro screen for pathogenicity.

Abstract: Novel methods and microorganisms are provided, where novel genetic mammalian cell invasive capability is imparted to a microorganism by the introduction of an exogenous inv or ail gene. The resulting organisms are then capable of binding to mammalian cells and are transferred to the cytoplasm. Other novel genetic capabilities may be imparted to the unicellular microorganism, which may serve as a vaccine for one or more pathogens or may introduce genetic capabilities or foreign molecules into a mammalian host cell. The sequences may be used for an in vitro screen for pathogenicity.

Abstract: An export sequence of export DNA can be identified by transforming a population of cells with a vector having a transposon that includes a structural gene encoding a detectable compound, positioned between insertion sequences. The structural gene encodes a detectable compound that, in wild-type organisms, is translated with an export peptide effective to export the compound. Since the transposon lacks DNA coding for an export sequence capable of exporting the detectable gene product, transformants that export the gene product include a DNA fusion of the transposon to export DNA from the parent cell, in a position to allow expression of the fused DNA. The transformants are analyzed to locate the export DNA or a gene comprising it, and the position of the export DNA in the cell's genome is determined; the orientation of the insertion also is determined.