| Chlamydia | |
|---|---|
| C. trachomatis inclusion bodies (brown) in a McCoy cell culture. | |
| Scientific classification | |
| Domain: | Bacteria |
| Class: | Chlamydiae |
| Order: | Chlamydiales |
| Family: | Chlamydiaceae |
| Genus: | Chlamydia[1]Jones et al. 1945 emend. Everett et al. 1999 |
| Species | |
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Chlamydia muridarum Everett et al. 1999 |
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Chlamydia is a genus of bacteria that are obligate intracellular parasites. Chlamydia infections are the most common bacterial sexually transmitted infections in humans and are the leading cause of infectious blindness worldwide.[2]
The three Chlamydia species include Chlamydia trachomatis (a human pathogen), Chlamydia suis (affects only swine), and Chlamydia muridarum (affects only mice and hamsters).[3]
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Because of Chlamydia's unique developmental cycle, it was taxonomically classified in a separate order.[4] Chlamydia is part of the Chlamydiales order, Chlamydiaceae family. As of March 2008, a new chlamydial agent has been proposed to be introduced into the Chlamidiaceae family, namely Candidatus Clavochlamydia salmonicola.[5]
Chlamydia has a genome size of approximately 500-1000 kilobases and contains both RNA and DNA.[4]
Chlamydia may be found in the form of an elementary body and a reticulate body. The elementary body is the non-replicating infectious particle that is released when infected cells rupture. The elementary body is responsible for the bacteria's ability to spread from person to person. This form is analogous to a spore. The elementary body may be 0.25 to 0.3 μm in diameter, and it mainly consists of C. trachomatis, C. pneumoniae and C. psittaci. This form is covered by a rigid cell wall and contains a DNA genome with a molecular weight of 66 × 107 (about 600 genes, one-quarter of the genetic information present in the DNA of Escherichia coli). It also contains a cryptic DNA plasmid with 7,498 base pairs. It also contains an open reading frame for a gene involved in DNA replication. In addition, the elementary body contains an RNA polymerase responsible for the transcription of the DNA genome after entry into the host cell cytoplasm and the initiation of the growth cycle. Ribosomes and ribosomal subunits are found in these bodies. The elementary body induces its own endocytosis upon exposure to target cells. It is estimated that one phagolysosome usually produces 100-1000 elementary bodies.
Chlamydia may also take the form of a reticulate body, which is in fact an intracytoplasmatic form, highly involved in the process of replication and growth of these bacteria. The reticulate body is slightly larger than the elementary body and may reach up to 0.6 μm in diameter with a minimum of 0.5 μm. It does not present a cell wall. When stained with iodine, reticulate bodies appear as inclusions in the cell. The DNA genome, proteins, and ribosomes are retained in the reticulate body. This occurs as a result of the development cycle of the bacteria. The reticular body is basically the structure in which the chlamydial genome is transcribed into RNA, proteins are synthesized, and the DNA is replicated. The reticulate body divides by binary fission to form particles which, after synthesis of the outer cell wall, develop into new infectious elementary body progeny. The fusion lasts about 3 hours and the incubation period may be up to 21 days. After division, the reticulate body transforms back to the elementary form and is released by the cell by exocytosis.[4]
Studies on the growth cycle of C. trachomatis and C. psittaci in cell cultures in vitro reveal that the infectious elementary body develops into a noninfectious reticulate body (RB) within a cytoplasmic vacuole in the infected cell. After the elementary body enters the infected cell, an eclipse phase of 20 hours occurs while the infectious particle develops into a reticulate body. The yield of chlamydial elementary bodies is maximal 36 to 50 hours after infection.[6]
Most commonly, chlamydial infections[7] do not cause symptoms. Usually, people who engaged in sexual activities with potentially infected individuals may request several tests to diagnose the condition.
Chlamydia can be detected through culture tests or non-culture tests. The main non-culture tests include Fluorescent Monoclonal Antibody Test, enzyme immunoassay, DNA probes, rapid Chlamydia tests and leukocyte esterase tests. Whereas the first test can detect the major outer membrane protein or the LPS, the second detects a colored product converted by an enzyme linked to an antibody. The rapid Chlamydia tests use antibodies against the LPS, the leukocyte esterase tests detect enzymes produced by leukocytes containing the bacteria in urine [4]).
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