Mycoplasmal, chlamydial, rickettsial, and ehrlichial pneumonias

Mycoplasmas and the various obligate and facultative intracellular bacteria that cause significant clinical pulmonary injury are quite diverse from the point of view of microbial genetics and phenotypes. Molecular analysis of the genetic similarity reveals that Rickettsia species of the typhus and spotted fever groups and Ehrlichia and Anaplasma species are relatively closely related and that Coxiella burnetii and Legionella pneumophila are genetically related to one another.1 However, Rickettsia and Coxiella species are only distantly related to one another and are even more distant from the genetically diverse Chlamydia and Mycoplasma.