Virulence ‐associated protein A from Rhodococcus equi is an intercompartmental pH‐neutralising virulence factor

AbstractProfessional phagocytic cells such as macrophages are a central part of innate immune defence. They ingest microorganisms into membrane ‐bound compartments (phagosomes), which acidify and eventually fuse with lysosomes, exposing their contents to a microbicidal environment. Gram‐positiveRhodococcus equi can cause pneumonia in young foals and in immunocompromised humans. The possession of a virulence plasmid allows them to subvert host defence mechanisms and to multiply in macrophages. Here, we show that the plasmid ‐encoded and secreted virulence‐associated protein A (VapA) participates in exclusion of the proton‐pumping vacuolar‐ATPase complex from phagosomes and causes membrane permeabilisation, thus contributing to a pH‐neutral phagosome lumen. Using fluorescence and electron microscopy, we show t hat VapA is also transferred from phagosomes to lysosomes where it permeabilises the limiting membranes for small ions such as protons. This permeabilisation process is different from that of known membrane pore formers as revealed by experiments with artificial lipid bilayers. We demonstrate that, at 24 hr of infection, virulentR.  equi is contained in a vacuole, which is enriched in lysosome material, yet possesses a pH of 7.2 whereas phagosomes containing avapA deletion mutant have a pH of 5.8 and those with virulence plasmid ‐less sister strains have a pH of 5.2. Experimentally neutralising the macrophage endocytic system allows avirulentR.  equi to...
Source: Cellular Microbiology - Category: Microbiology Authors: Tags: RESEARCH ARTICLE Source Type: research