Chlamydia

Abstract This chapter focuses on the important human pathogens within the genus Chlamydia , as well as on Parachlamydia acanthamoebae , Waddlia chondrophila , and Simkania negevensis , for which evidence gathered over the past 20 years supports possible pathogenicity in humans. The taxonomy of Chlamydiales is rapidly evolving and progressively moving from a purely phenotypic taxonomy to a polyphasic taxonomy combining phenotypic, molecular, and phylogenetic characteristics. Chlamydia , Parachlamydia , Waddlia , and Simkania all present biphasic developmental stages with elementary body and reticulate body formation. Chlamydia trachomatis is the most common bacterial agent of sexually transmitted infection in the world. Chlamydia psittaci causes a wide variety of clinical conditions in humans, ranging from asymptomatic infection to severe, even fatal pneumonia and systemic infections. For Chlamydia trachomatis , one effective method for identification of the organism in cell culture is to stain the monolayers with species‐specific fluorescein‐conjugated monoclonal antibodies.