Bacteria wield all sorts of molecular weapons that allow them to infiltrate their hosts. But one microbe – Salmonella enterica – has a particularly devious trick. It uses weapons that arm themselves by manipulating the host’s own proteins. When this bacterium infects cells, it turns them into accomplices to their own downfall.

One of these injected weapons is known appropriately enough as SipA, or Salmonella invasion protein A. It has two business ends, both of which pose a threat to a host cell. One of them causes a host protein called actin to clump together into long filaments. These act as guide ropes that help to draw Salmonella into the cell. The other end of SipA causes white blood cells to