**3. Conclusion**

*Chlamydia* spp. are the culprit of many human infections with severe complications, especially involving human eye, reproductive system, and lungs. Many virulence factors of the bacterium have been described in literature. Those virulence factors facilitate invasion in human tissues and provide the microorganism with the ability to hide from immune system and use the host cell mechanisms in its favor. The cell wall structure, Type III secretion systems, chlamydial proteins present in the cytosol of infected cells, induction of antiapoptotic activity of infected host cells, chlamydial cryptic plasmid, protein CT135, silencing of the NF-κB inflammatory pathway, Translocated actin recruiting protein (TarP), chlamydial polymorphic outer membrane proteins (Pmps), are some of them. Elucidation of the mechanisms of pathogenicity may lead to the development of new ways to face this major pathogen.
