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Chlamydia (bacterium)
Encyclopedia
Chlamydia is a genus
of bacteria
that are obligate intracellular parasite
s. Chlamydia infections are the most common bacterial sexually transmitted infections in humans and are the leading cause of infectious blindness worldwide.
The three Chlamydia species
include Chlamydia trachomatis
(a human pathogen), Chlamydia suis
(affects only swine
), and Chlamydia muridarum
(affects only mice
and hamster
s). Prior to 1999, the Chlamydia genus also included the species that are presently in the genus Chlamydophila
: Two clinically relevant species, Chlamydophila pneumoniae
and Chlamydophila psittaci
were moved to the Chlamydophila genus.
Chlamydia is part of the Chlamydiales order, Chlamydiaceae family, along with Chlamydophila genus. As of March 2008, a new chlamydial agent has been proposed to be introduced into the Chlamidiaceae family, namely Candidatus Clavochlamydia salmonicola.
and DNA
.
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.
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.
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
).
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
that are obligate intracellular parasite
Obligate intracellular parasite
Intracellular parasites are parasitic microorganisms - microparasites that are capable of growing and reproducing inside the cells of a host.-Facultative:...
s. Chlamydia infections are the most common bacterial sexually transmitted infections in humans and are the leading cause of infectious blindness worldwide.
The three Chlamydia species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
include Chlamydia trachomatis
Chlamydia trachomatis
Chlamydia trachomatis, an obligate intracellular human pathogen, is one of three bacterial species in the genus Chlamydia. C. trachomatis is a Gram-negative bacteria, therefore its cell wall components retain the counter-stain safranin and appear pink under a light microscope.The inclusion bodies...
(a human pathogen), Chlamydia suis
Chlamydia suis
Chlamydia suis is a member of the genus Chlamydia. C. suis has only been isolated from swine, in which it may be endemic. Glycogen has been detected in Chlamydia suis inclusions in infected swine tissues and in cell culture. C...
(affects only swine
Pig
A pig is any of the animals in the genus Sus, within the Suidae family of even-toed ungulates. Pigs include the domestic pig, its ancestor the wild boar, and several other wild relatives...
), and Chlamydia muridarum
Chlamydia muridarum
Chlamydia muridarum is an intracellular bacterial species that at one time belonged to Chlamydia trachomatis. However, C. trachomatis naturally only infects humans and C...
(affects only mice
Mouse
A mouse is a small mammal belonging to the order of rodents. The best known mouse species is the common house mouse . It is also a popular pet. In some places, certain kinds of field mice are also common. This rodent is eaten by large birds such as hawks and eagles...
and hamster
Hamster
Hamsters are rodents belonging to the subfamily Cricetinae. The subfamily contains about 25 species, classified in six or seven genera....
s). Prior to 1999, the Chlamydia genus also included the species that are presently in the genus Chlamydophila
Chlamydophila
Chlamydophila is a bacterial genus belonging to the family Chlamydiaceae, order Chlamydiales, class/phylum Chlamydiae.-Taxonomy:Chlamydophila was recognized in 1999, with six species in Chlamydophila and three in the original genus, Chlamydia...
: Two clinically relevant species, Chlamydophila pneumoniae
Chlamydophila pneumoniae
Chlamydophila pneumoniae is a species of Chlamydophila, an obligate intracellular bacteria that infects humans and is a major cause of pneumonia....
and Chlamydophila psittaci
Chlamydophila psittaci
Chlamydophila psittaci is a lethal intracellular bacterial species that may cause endemic avian chlamydiosis, epizootic outbreaks in mammals, and respiratory psittacosis in humans. Chlamydophila psittaci is transmitted by inhalation, contact or ingestion among birds and to mammals...
were moved to the Chlamydophila genus.
Classification
Because of Chlamydia's unique developmental cycle, it was taxonomically classified in a separate order.Chlamydia is part of the Chlamydiales order, Chlamydiaceae family, along with Chlamydophila genus. As of March 2008, a new chlamydial agent has been proposed to be introduced into the Chlamidiaceae family, namely Candidatus Clavochlamydia salmonicola.
Genome structure
Chlamydia has a genome size of approximately 500-1000 kilobases and contains both RNARNA
Ribonucleic acid , or RNA, is one of the three major macromolecules that are essential for all known forms of life....
and DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
.
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
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
. 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
Cell wall
The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds some types of cells. It is located outside the cell membrane and provides these cells with structural support and protection, and also acts as a filtering mechanism. A major function of the cell wall is to...
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
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
). 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
Cytoplasm
The cytoplasm is a small gel-like substance residing between the cell membrane holding all the cell's internal sub-structures , except for the nucleus. All the contents of the cells of prokaryote organisms are contained within the 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
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
, 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.
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.
Pathology
Most commonly, chlamydial infections 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
Leukocyte esterase
Leukocyte esterase is a urine test for the presence of white blood cells and other abnormalities associated with infection.White blood cells in the urine usually indicate a urinary tract infection. The leukocyte esterase test detects esterase, an enzyme released by white blood cells. Positive...
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
Urine
Urine is a typically sterile liquid by-product of the body that is secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream...
).