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Self-Study STD Module - Chlamydia

Pathogenesis and Microbiology

Classification of Chlamydia Species

Chlamydia trachomatisis a member of the Chlamydiaceae family. There is one genus Chlamydia containing three species that infect humans: C. pneumoniae, C. psittaci,and C. trachomatis.

C. pneumoniae and C. psittaci cause pneumonia. C. trachomatis causes trachoma in all ages, genital infections, lymphogranuloma venerum (LGV), and conjunctivitis in adults, and conjunctivitis and pneumonia in neonates.


Chlamydiae are obligate intracellular bacteria with a Gram-negative-like cell wall. Chlamydia generally infects the columnar epithelial cells and often becomes chronic, lasting months to more than a year if untreated.

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Life Cycle of Chlamydia

Life Cycle

The life cycle of C. trachomatisis 72 hours. It requires that the bacteria live within a host cell and that they survive by replication that results in the death of the cell.

More specifically, the life cycle is as follows:

  • The elementary body (EB), a small infectious particle found in secretions, attaches to and enters a cell such as an endocervical or urethral cell.
  • Within eight hours, the EB transforms into a reticulate body (RB), which begins to multiply within an isolated area called an inclusion.
  • Within 24 hours, some RBs reorganize back to EBs, and, as the cell wall bursts, the EBs are released to infect adjacent cells or to be transmitted to and infect another person.

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Page last modified: December, 2009
Page last reviewed: December, 2009

Content Source:Division of STD Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention

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