Conserved type III secretion system exerts important roles in Chlamydia trachomatis.

Upon infection, Chlamydiae alter host cellular functions in a variety of ways. Chlamydial infection prevents host cell apoptosis, induces re-organization of the actin cytoskeleton and alters host cellular signaling mechanisms. Chlamydia is among the many pathogenic Gram-negative bacteria that employ the type III secretion system (T3SS) to overcome host defenses and exploit available resources. T3SS are used by many Gram-negative bacterial pathogens to manipulate eukaryotic host cells through the delivery of effector proteins into their cytosol and membranes. T3SS is an evolutionarily refined, virulence determinant of Gram-negative bacteria where more than 20 proteins form an apparatus, generally termed injectisome, to achieve the vectorial secretion and translocation of anti-host effector proteins. This review describes challenges and recent advances that have revealed how Chlamydia trachomatis utilizes diversification to produce a conserved T3SS that exerts an important role in Chlamydia trachomatis.