New Bacterial Exit Strategy

Microbes that cause tuberculosis, as well as many other bacterial pathogens, like to grow and replicate inside the cells of their mammalian hosts, far from the immune system's reach. But when the time comes for a young bacterium to venture out and infect a new host cell, the bug's exit strategy must be carefully considered. If the bacterium breaks apart the cell to escape, then the host's immune system will be tipped off. A team of cell biologists led by Thierry Soldati of the University of Geneva is now reporting a newly discovered stealth departure route for Mycobacterium tuberculosis (Science 2009, 323, 1729). As the TB bacterium exits amoeba cells, which are a model for the human cells infected by the pathogen, Soldati and colleagues found that it orchestrates the construction of a so-called ejectosome, a barrel-shaped pore across the cell membrane. The pore allows the bacterium to squeeze out without causing damage or setting off an immune-system alarm. The ejectosome consists of proteins secreted by the bacterium along with actin proteins found in the host cell. Understanding this tuberculosis exit strategy is expected to offer ways to thwart it.