Project Summary. The Gram-negative bacterium Acinetobacter baumannii is a leading cause of infections in both the hospital setting and in injured military personnel. The goal of this Research Career Scientist Award is to continue addressing the mechanisms that regulate virulence and β−lactam resistance in A. baumannii. A high-frequency switch that regulates the transition between virulent (opaque) and avirulent (translucent) forms of A. baumannii will be studied using a combination of genetic and biochemical approaches. We have identified a central role for a family of TetR-type transcriptional regulators in controlling the virulence switch. The regulatory network controlling these TetR regulators will be studied. In addition, we have genetically locked strains in the avirulent state and demonstrated that they serve as a highly effective live attenuated vaccine. My lab will address the immunologic parameters that make our vaccine more effective than a heat killed vaccine. In a second project, our work has found that β-lactamase expressing A. baumannii exhibit changes in cell wall structure and this results in new collateral vulnerabilities in the cell. We have identified genes that now become essential only in β-lactamase expressing cells and identified a small molecule that specifically kills β-lactamase expressing bacteria. The above gene products represent an entirely new set of bacterial targets for the development of novel antimicrobials. These research projects are highly collaborative and involve VA investigators at both the Atlanta VAMC and the Louis Stokes VAMC in Cleveland, OH. This project will continue to foster these collaborations and allow for the development of new projects. This project will also have an important training component, where the mentoring of three CDA-2-funded VA investigators will be provided. Lastly, student and postdoctoral training will continue to be an integral component of this research plan, with the goal of developing the next generation of VA scientists.