Survival strategies of intracellular bacterial pathogens

The common false dichotomy is that bacteria grow either intracellularly or extracellularly, and though there are some bacteria that have an almost viral-like dependency on host cells for metabolites, most can exploit both replicative niches. The facultative intracellular pathogens that preferentially replicate inside cells have evolved mechanisms that defeat or suppress the natural antibacterial cell biology processes associated with endosomal or phagosomal residency, and the nutritional limitations that might be brought about by entrapment within a lipid-bounded vacuole. This chapter describes how bacteria have adapted to intracellular replication and how they use sophisticated protein secretion apparatus and effector molecules, trigger uptake into cells, prevent killing by natural antibacterial processes, subvert host immunity, and replicate to cause some of the most important diseases of humankind, such as tuberculosis and dysentery.