Salmonella survives the macrophage's acid attack

Macrophages destroy bacteria by engulfing them in intracellular compartments, which they then acidify to kill or neutralize the bacteria. However, some pathogenic bacteria, such as Salmonella enterica, have evolved to exist and even grow while within these acidified compartments. Yet, how Salmonella responds to the acidic environment and how that environment affects the virulence of this pathogen are unclear. New research reveals that Salmonella fights acid with acid, by lowering the pH of its own interior in response to the acidification of the Salmonella-containing compartment by the macrophage, and by using that low pH as a signal to turn on genes needed to establish an infection.

To investigate the effect of the acidic environment on Salmonella, the authors used a biosensor, called an I-switch, which allowed for measurements of pH within a single cell. Using the I-switch, the authors found that the Salmonella cytoplasm acidifies rapidly after being engulfed and exposed to the acidic environment of the macrophage interior. Interestingly, they found that the Salmonella actively, as opposed to passively, acidify their cytoplasm.

Researchers found that bacteria can survive a cytoplasmic pH of 5.6 and that they even use this to signal expression of virulence genes. The research shows that low pH activates an intracellular signalling cascade, which induces the formation of a nanomachine called the type III secretion system. This nanomachine is composed of a needle complex used to inject bacterial virulence proteins into the host cell.

For further details, see Phys.Org.

Posted by Tim Sandle