**5. Classification**

The genus Chlamydia has been described in the Chlamydiaceae family of the order Chlamydiales. Chlamydiae are classified according to their antigenic structures, sulfonamide resistance, host differences, and the diseases they cause. Characteristics of three species infecting humans have been identified:

*Chlamydia trachomatis* has intracytoplasmic inclusion bodies containing glycogen. They are inhibited by sulfonamides. They cause eye and genital infections in adults and conjunctivitis and pneumonia in infants.

*Chlamidiae (Chlamydophila) pneumoniae* have intracytoplasmic inclusion bodies that lack glycogen. It is generally resistant to sulfonamides. It causes respiratory tract infections in humans.

*Chlamidiae (Chlamydophila) psittaki,* contain dense intracytoplasmic inclusions devoid of glycogen. It is generally resistant to sulfonamides. It causes psittacosis in humans and ornithosis in birds [11].
