**2. Structure, life cycle**

Chlamydia cell wall is rich in lipids like gram-negative bacteria. It does not contain typical bacterial peptidoglycan. It contains N-acetylmuramica acid. They exist in two forms in their life cycle. Elementary body (EC) is the form that is metabolically inactive, resistant to environmental conditions and infective. Reticular Body (RC) is the metabolically active, intracellular proliferative and non-infective form. Elementary bodies show a high affinity for host epithelial cells. Bacterial major outer membrane proteins (major outer membran protein-MOMP, OmcB, PmpD), on the surface of *Chlamydia trachomatis* interact with host cell receptors (heparan sulfate, proteoglycans, mannase-6-phosphate receptors, and growth factor such as receptors) and enter the cell rapidly. They are then taken up into the cell by receptor-mediated endocytosis or pinocytosis. Meanwhile, they are protected from the environment by inhibiting lysosome fusion. In the cell, the EC transforms into a reticular body. The reticular bodies are larger in size and multiply by dividing each into two, forming an intracytoplasmic inclusion. They leave the cell to infect new cells. This cycle takes 24–48 h [10].
