Chlamydia trachomatis


Chlamydia Trachomatis is the organism responsible for diseases such as trachoma and the STD Chlamydia. Chlamydia is the most common STD in the United States, with about 4 million new cases diagnosed every year.

The Organism & Life Cycle 

Chlamydia are obligate intracellular parasites, and are among the smallest living organisms. There are two stages in the life of Chlamydia: elementary bodies and reticulate bodies. Another feature of Chlamydia is that they are unable to synthesize their own energy (ATP) and are completely dependent on their host for energy. The organism is in the elementary stage of its life when it encounters its host and is taken up by phagocytosis. It prevents the fusion of the phagosome and lysosome; this is what normally kills pathogens. Once the phagolysosome formation is stopped, the bacteria secrete glycogen and transform into the reticulate body. Reticulate bodies obtain their energy by sending forth “straw-like” structures into the host cell cytoplasm, and they divide by binary fission. Each phagolysosome produces about 100-1000 reticulate bodies.

Virulence Factors

chlamydiaThe cell wall of Chlamydia has been characterized as gram negative with a notable difference: it lacks muramic acid that is found in the cell walls of most other bacteria. This makes Chlamydia resistant to _-lactam antibiotics such as penicillin, because such antibiotics disrupt the “typical” cell wall, which includes muramic acid. Being gram-negative, it also contains LPS, which helps cause damage to the host’s body(mainly due to the host’s immune response). Once inside the host, chlamydia bind sialic acid receptors, which are usually found in mucous-rich environments. Antigenic variation is also an important factor, with 15 known serotypes. A disadvantage to humans is that as many as 75% of the infections may be sub-clinical and asymptomatic, but infectious nonetheless.

Encounter, Diseases and Epidemiological Data

The most common way to get Chlamydia is through sexual intercourse with an affected individual. Newborns may get infected by affected mothers during childbirth. Typically, it causes pelvic inflammatory disease (PID) in women, which is a result of the host’s inflammatory response. Other diseases include ocular infections such as conjunctivitis and blindness. Neonates are especially vulnerable to conjunctivitis and pneumonia if the mother is infected. Trachoma is a disease that is caused by inflammation in the conjunctiva and subsequent scarring of the cornea, which could lead to blindness.
A more serious disease called lymphogranuloma venereum (when Chlamydia cause lesions in the genital mucosa and enter it) is also caused by Chlamydia, but it is not endemic in the developed world. People with Gonorrhoea are susceptible to a chlamydial infection. Females aged 15-24 (USA) are most susceptible to Chlamydia. Incidence rate and prevalence are highest among blacks.


The most important form of treatment is prevention, which can be done by discouraging multiple sexual partners, and possibly abstinence from sex for those who are known to be infected. Other forms of prevention would include setting up information programs, especially in inner-city communities, where prevalence of Chlamydia is very high. Chlamydia is difficult to eradicate because it is an intracellular parasite, which means that any administered antibiotic must cross the host cell membrane and kill the bacterium without damaging the host cell. The drugs of choice are tetracyclines, erythromycin and sulfonamides. These drugs should be administered not only to the infected person, but also all of their sexual partners. For pregnant women and neonates (that are infected with Chlamydia), erythromycin is the drug of choice. Chlamydia may be difficult to completely eradicate, but in the past few years, the incidence rates have been steady, and with planning and spreading information about it, we can attack the overwhelming incidence rate and curb the spread of Chlamydia.


1) CDC. Recommendations for the Prevention and Management of Chlamydia trachomatis Infections, 1993

2) Schaechter, Engleberg, Eisenstein, and Gerald Medoff (1999). Mechanisms of 
Microbial Disease. Third Edition. Lippincott Williams and Wilkins, Philadelphia.

3) MedlinePlus Medical Encyclopedia.