Discovery and characterization of an essential Francisella tularensis protein required for tularemia disease development (538.5)

Potential bioterrorism agent Francisella tularensis subspecies tularensis ( F. tularensis ) causes tularemia; a disease that can cause up to 60% mortality. An essential step to developing tularemia is the ability of F. tularensis to escape the vacuole that it initially occupies to replicate in the cytosol of epithelial cells. We hypothesize F. tularensis possesses virulence factors (VFs) that facilitate this process. In this study, we identified a crucial VF for tularemia development. To identify this VF, we screened a 3,050 Francisella mutant library for microbes deficient in bacterial replication once inside host cells. By using subsequent bioinformatics analysis we identified proteins in a subset of mutated bacteria that fit traits of VFs and we tested their ability to cause tularemia‐induced death in mice. Mice infected with bacteria inactivated in 1 novel gene appeared uninfected whereas wild‐type infected mice died within 2 days. Electron and immunofluorescence micrographs of infected hepatocytes showed that this gene aids the bacteria in exiting lysosome‐associated membrane protein‐1 (LAMP‐1) positive membrane vacuoles leading to bacterial replication in the cytosol. Our findings demonstrate this novel VF enables F. tularensis to escape into the cytosol and ultimately cause disease.