Breaking and exiting

Abstract

Some bacteria, including Salmonella and Shigella spp., can take up residence within vacuoles inside mammalian host cells. To gain access to the nutrient-rich host cytosol, the internalized bacteria must break out from their vacuole, but how? Ellison et al. used super-resolution live-cell imaging and correlative light and electron microscopy to characterize this process. They developed a reporter for the host lipid sphingomyelin, which is normally found on extracellular-facing membranes. The authors found that sphingomyelin became exposed to the cytosol on bacteria-containing vacuoles. This exposure occurred just before the vacuoles ruptured, releasing the bacteria into the cytosol. Sphingomyelin exposure can thus be used as an early indicator of bacterial invasion and potentially more widely as an indicator of membrane damage that threatens the integrity of the cytosol.