Francisella bacteria encode genes required for efficient invasion and intracellular replication in hepatocytes

Abstract

Francisella tularensis is a bacterium that can cause up to 60% mortality in humans. These microbes carry a cluster of conserved genes present in all F. tularensis subspecies called the Francisella pathogenicity island (FPI). Within the FPI, iglB, iglC, pdpA and vgrG genes are important for intracellular macrophage survival and virulence; yet, their role in epithelial cell infections, a major contributor to the progression of disease, is unclear. Given that F. tularensis uses dissimilar mechanisms to enter different cell types, we hypothesized that FPI genes play a crucial role in bacterial entry into epithelial cells. To test this hypothesis, BNL CL.2 hepatocytes were infected with F. novicida for up to 48 h. Detailed microscopic examination and gentamicin protection assay revealed that ΔiglB, ΔiglC, ΔvgrG, ΔpdpA Francisella mutants were invasion and replication deficient. We showed that gene complementation restored intracellular growth. Our data suggest that IglB, IglC, PdpA and VgrG are important for hepatocyte infections, as they are vital for efficient invasion and intracellular proliferation.Grant Funding Source: NSERC, CIHR