BACTERIA CHLAMYDIA TRACHOMATIS

Bacteria Chlamydia Trachomatis

Bacteria Chlamydia Trachomatis

What is Chlamydia trachomatis?

Chlamydia trachomatis is a small bacterium that cannot grow outside a living cell. In this respect it resembles a virus, but it is actually a very sophisticated organism. There are two other related organisms: Chlamydia psittaci is widespread in animals and can be transmitted to humans.

This organism in humans is an uncommon cause of severe pneumonia particularly when acquired from infected birds of the parrot (Psittacine) family, and occasionally of abortion following contact with infected sheep. The more recently described Chlamydia pneumoniae (also known as the TWAR agent - Taiwan Acute Respiratory, after the designations of the first two isolates), may prove to be a frequent cause of upper and lower respiratory infection transmitted from person to person by infected droplets (Budai, 2007).

History and Biological Background

Chlamydia is caused by the bacterium Chlamydia trachomatis. The word chlamys is Greek for "cloak draped around the shoulder." This describes how the intracytoplasmic inclusions caused by the bacterium are "draped" around the infected cell's nucleus. Because the symptoms of the disease resemble other pathologies, chlamydia was not recognized as a sexually transmitted disease until recently. Isolation from embryonated eggs in 1957 and from cell culture in 1963 confirmed its existence as a bacterium. However, since the organism is an obligate intracellular parasite that exclusively infects humans (it cannot synthesize its own ATP or grow on artificial medium), it was once thought to be a virus. Because of Chlamydia's unique developmental cycle, it was taxonomically classified in a separate order.

It can thus be found with the other well-known intracellular parasites, rickettsiae, in diagnostic manuals. Chlamydia has a genome size of approximately 500-1000 kilobases and contains both RNA and DNA. The organism is also extremely temperature sensitive and must be refrigerated at 4 C as soon as a sample is obtained (Fredlund, 2004).

Virulence Factors

There are numerous factors that contribute to the pathogenicity of Chlamydia trachomatis. Colonization of Chlamydia begins with attachment to sialic acid receptors on the eye, throat, or genitalia. It persists at body sites that are inaccessible to phagocytes, T-cells, and B-cells. It also exists as 15 different serotypes. These serotypes cause four major diseases in humans: endemic trachoma (caused by serotypes A and C), sexually transmitted disease and inclusion conjunctivitis (caused by serotypes D and K), and lymphogranuloma venereum (caused by serotypes L1, L2, and L3). Endemic trachoma leads to blindness, whereas inclusion conjunctivitis is associated with the sexually transmitted form and does not lead to blindness (Fredlund, 2004).

Its unique cell wall structure is another virulence factor. Studies reveal that Chlamydia, because of its cell wall, is able to inhibit phagolysosome fusion in phagocytes. The cell wall is proposed to be gram-negative in that it contains an outer lipopolysaccharide membrane, but it lacks peptidoglycan in its cell wall. This lack of peptidoglycan is shown by the inability to detect muramic acid and antibodies directed against it. It may, however, contain a carboxylated sugar other than muramic ...