A Primary Investigation On The Intracellular Interaction Between Edwardsiella Tarda And Macrophge Cell

Edwardsiella tarda is an intracellular bacterial pathogen. It could reside and replicate in macrophage, which is important for its pathopoiesis. However, the intracellular process and mechanism of E. tarda interacting with macrophage is largely unknown. In this work, we demonstrated that E. tarda resided and replicated within a membrane-bound vacuole, named by the Edwardsellia-containing vacuole (ECV). Internalized Edwardsellia tarda displayed heterogeneous replication, with a subpopulation of E. tarda hyper-replicating in less than30%macrophage cells. Hyper-replicated E. tarda induced an inflammatory cell death characterized by caspase-1activation and the release of IL-1β, and the important outcome was the release of free E. tarda from the confine of the macrophage. Interestingly, unlike the in vitro cultured bacteria, the macrophage-escaped E. tarda induced a rapid cell death dependent on capspase-3and cathepsin B/D in a secondary infection, and resisted extensive host-killing mechanisms including reactive oxygen species (ROS), acidic environment, serum complements and polymorphonuclear leukocyte or neutrophils (PMNs). Further in vivo assays demonstrated that macrophage-escaped E. tarda built a commanding lead over the in vitro cultured E. tarda in co-infected mice model, and were highly lethal to infected mice. These results indicated that E. tarda released from macrophage were invasion-primed. Subsequent transcriptional profile comparison revealed that virulence-related type III secretion system, type VI secretion system and other stress resistance-associated genes were obviously induced in macrophage-escaped E. tarda, which could be responsible for the output of invasion-priming. Taken together, our work elucidated that E. tarda utilized macrophage as a niche for replication and invasion-priming, which could serve as a reservoir for dissemination.