Spreading of a virulence lipid into host membranes promotes mycobacterial pathogenesis

Several lipids of the pathogen Mycobacterium tuberculosis are known to promote virulence at various stages of disease. However, the inability to probe these lipids during in vivo infection makes elucidation of their pathogenic mechanisms difficult. Using chemical extraction and reconstitution methods, we were able to define the lipid composition of the outer mycomembrane of Mycobacterium marinum prior to infection. Combining this approach with the synthesis of clickable, semi-synthetic lipids, we introduced a chemically tractable, biologically active variant of the virulence lipid phthiocerol dimycocerosate (PDIM) into the mycomembrane. We find that following infection of zebrafish larvae, PDIM spreads away from bacterial surfaces into the membranes of both macrophage and epithelial cells that it contacts. This spreading facilitates PDIM’s role in preventing bacterium-detrimental immune activation at the site of infection.