Small molecule inhibitors of type III secretion in Yersinia block the Chlamydia pneumoniae infection cycle.

Intracellular parasitism by Chlamydiales is a complex process involving transmission of metabolically inactive particles that differentiate, replicate, and re-differentiate within the host cell. A type three secretion system (T3SS) has been implicated in this process. We have here identified small molecules of a chemical class of acylated hydrazones of salicylaldehydes that specifically blocks the T3SS of Chlamydia. These compounds also affect the developmental cycle showing that the T3SS has a pivotal role in the pathogenesis of Chlamydia. Our results suggest a previously unexplored avenue for development of novel anti-chlamydial drugs.