Abstract: Attenuated strains of Gram negative bacteria carrying a mutation in one or more ysc genes or homologs are provided, as are methods of use for immunization against infection with a pathogenic strain and for delivery of a therapeutic agent.

Abstract: Attenuated strains of Gram negative bacteria carrying a mutation in one or more ysc genes or homologs are provided, as are methods of use for immunization against infection with a pathogenic strain and for delivery of a therapeutic agent.

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 ail or hil 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. Mutant microorganisms having an attenuated invasive phenotype are also disclosed wherein one or more invasive genes have been modified.

Abstract: Nucleic acids encoding all or part of a Yersinia ail gene are provided. The nucleic acid comprises at least 50 base pairs of a Yersinia ail gene in isolated form or consists or a fragment consisting essentially of at least 50 base pairs but not more than 50 kilo base pairs of a Yersinia ail gene. Such nucleic acids can also be operably linked to transcriptional and translational initiation and termination sequences which are functional in a microorganism host.