Several pathogenic or opportunistic bacteria can induce or inhibit host cell apoptosis. The modulation of cellular pathways that results in the induction or delay of host cell apoptosis is an important mechanism of bacterial virulence. These processes can be mediated by various host cell signaling pathways that are subverted by the bacteria. Pathogens can activate apoptotic proteins such as caspases, inactivate anti-apoptotic proteins such as NFκB and mitogen-activated protein kinases, or up-regulate the endogenous receptor/ligand system that induces apoptosis, generally when the bacteria are bound to the host cell surface. Bacteriainduced apoptotic or anti-apoptotic processes are often related to the ability of the bacteria to reach the host tissues. However, since apoptosis is also involved in host defense mechanisms against infectious agents, this phenomenon apparently plays a central role in host-pathogen interactions.