Bacterial Injection Machines

The delivery of virulence factors directly into host cells is a fascinating aspect of pathogenesis. For Gram-negative bacteria to translocate virulence factors into host cells, at least three membranes must be passed (two bacterial and a host plasma membrane). Bacterial injection machines deliver virulence factors to a specific cellular location where they intersect and influence host mechanisms. This minireview focuses on the Gram-negative bacterial translocation systems that mediate type III and type IV secretion.