Law H T, Sriram Aarati, Fevang Charlotte, Nix Eli B, Nano Francis E, Guttman Julian Andrew
Department of Biological Sciences, Simon Fraser University, Burnaby, British Columbia, Canada.
Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada.
PLoS One. 2014 Aug 12;9(8):e104881. doi: 10.1371/journal.pone.0104881. eCollection 2014.
The highly infectious bacteria, Francisella tularensis, colonize a variety of organs and replicate within both phagocytic as well as non-phagocytic cells, to cause the disease tularemia. These microbes contain a conserved cluster of important virulence genes referred to as the Francisella Pathogenicity Island (FPI). Two of the most characterized FPI genes, iglC and pdpA, play a central role in bacterial survival and proliferation within phagocytes, but do not influence bacterial internalization. Yet, their involvement in non-phagocytic epithelial cell infections remains unexplored. To examine the functions of IglC and PdpA on bacterial invasion and replication during epithelial cell infections, we infected liver and lung epithelial cells with F. novicida and F. tularensis 'Type B' Live Vaccine Strain (LVS) deletion mutants (ΔiglC and ΔpdpA) as well as their respective gene complements. We found that deletion of either gene significantly reduced their ability to invade and replicate in epithelial cells. Gene complementation of iglC and pdpA partially rescued bacterial invasion and intracellular growth. Additionally, substantial LAMP1-association with both deletion mutants was observed up to 12 h suggesting that the absence of IglC and PdpA caused deficiencies in their ability to dissociate from LAMP1-positive Francisella Containing Vacuoles (FCVs). This work provides the first evidence that IglC and PdpA are important pathogenic factors for invasion and intracellular growth of Francisella in epithelial cells, and further highlights the discrete mechanisms involved in Francisella infections between phagocytic and non-phagocytic cells.
高传染性细菌土拉弗朗西斯菌可定殖于多种器官，并在吞噬细胞和非吞噬细胞内复制，从而引发兔热病。这些微生物含有一组保守的重要毒力基因簇，称为弗朗西斯菌致病岛（FPI）。两个最具特征的FPI基因iglC和pdpA在吞噬细胞内细菌的存活和增殖中起核心作用，但不影响细菌的内化。然而，它们在非吞噬性上皮细胞感染中的作用仍未得到探索。为了研究IglC和PdpA在上皮细胞感染期间对细菌侵袭和复制的功能，我们用新凶手弗朗西斯菌和土拉弗朗西斯菌“B型”活疫苗株（LVS）缺失突变体（ΔiglC和ΔpdpA）及其各自的基因互补体感染肝和肺上皮细胞。我们发现，任一基因的缺失均显著降低了它们在上皮细胞中的侵袭和复制能力。iglC和pdpA的基因互补部分挽救了细菌的侵袭和细胞内生长。此外，在长达12小时的时间内都观察到大量LAMP1与这两种缺失突变体相关联，这表明IglC和PdpA的缺失导致它们从LAMP1阳性含弗朗西斯菌液泡（FCV）解离的能力存在缺陷。这项工作首次证明IglC和PdpA是弗朗西斯菌在上皮细胞中侵袭和细胞内生长的重要致病因素，并进一步突出了吞噬细胞和非吞噬细胞之间弗朗西斯菌感染所涉及的不同机制。
