FIG. 8.

A model of growth-phase-dependent cytolysis of mammalian cells by L. pneumophila upon termination of intracellular bacterial replication to egress from the spent host cell. During early stages of formation of the mitochondria and rough endoplasmic reticulum-surrounded phagosome (A) and during exponential intracellular replication (B), expression of the pore-forming activity is turned off, but caspase-3-mediated apoptosis is triggered. Upon transition to the postexponential phase of growth, expression of the pore-forming activity is triggered, which results in insertions of pores in the phagosomal membrane first (C), leading to its disruption (D). This is followed by insertions of the pores in the plasma membrane (E), leading to osmotic lysis of the cell and release of the intracellular bacteria.