Identification of genes essential for Francisella invasion of non‐phagocytic cells

Abstract

The intracellular bacterium Francisella tularensis subspecies tularensis (F. tularensis) is the causative agent of tularemia, a disease that can result in 30–35% mortality if left untreated. F. tularensis host cell invasion is crucial for their pathogenesis as without invasion disease does not occur. Upon host entry, the bacteria colonize both macrophages and epithelial cells. We hypothesize F. tularensis possesses unique virulence factors specific for the invasion of epithelial cells. To identify F. tularensis genes involved in this process, we utilized both in vitro and in vivo experimental approaches using a biosafety level 2 bacterial surrogate, F. tularensis subspecies novicida (F. novicida). A F. novicida mutant library was screened for bacteria with reduced invasion and intracellular growth using gentamycin‐based survival assays in hepatocytes in vitro. Select candidate mutants were tested in mice for their ability to colonize murine livers. We discovered that bacteria containing mutations in at least 6 previously uncharacterized genes had significantly reduced bacterial loads, resulting in mice that survived for extended durations as compared to wild‐type infections. Our findings demonstrate that novel bacterial proteins are crucial for Francisella virulence and these findings open a new door to the discovery of novel targets for the development of therapeutics and prophylactics.Grant Funding Source : NSERC and CIHR