Chlamydiae are obligatory, aerobic, intracellular parasites of eukaryotic cells.Chlamydiae are obligatory, aerobic, intracellular parasites of eukaryotic cells.They are small gram- negative cocci or rod- shaped, non- motile bacteria.Chlamydiae exhibits intermediate characteristics between bacteria and viruses.They are widespread in the natural world and are parasites of people, animals and tropical birds for squamous epithelial cells and macrophages of the respiratory and gastrointestinal tract.
The following properties it recognized as bacteria
- It has both DNA and RNA
- It has cell walls( like Gram Negative Bacteria) and ribosomes.
- It also replicate by binary fission
- Susceptible to antibiotics
There are three existing species thus : C. trachomatis, Chlamydophila psittaci, Chlamydophila pneumoniae. Chlamydia trachomatis has two biovars; TRIC and LGV.
Structure of Chlamydiae
Chlamydiae have a cytoplasmic membrane and an external membrane similar to Gram- negative bacteria, but lack a peptidoglycan cell wall.Chlamydiae can not synthesize their own ATP and require intracellular residence to remain viable.Chlamydiae exist in two forms: the elementary body and the reticular body.Both play a pivotal role in the life cycle of chlamydia.Although Gram negative, Chlamydiae stains better with Castaneda, Macchiavello or Gimenez stains.
Elementary body (EB)
The elementary body is the dispersal form, analogous to a spore. This dispersal shape is about 0.3 μm or 200- 300 nm in diameter. It is the extracellular infectious form. It induces its own endocytosis when exposed to target cells.
Reticulate body (RB)
The intracellular, multiplicative form is the reticulate body. It represents the non- infectious form of growth.
Life cycle of Chlamydiae
The life cycle of Chlamydia trachomatis consists of two stages: the elementary body and the reticulate body.After endocytosis into the host cell, EB prevents phagolysosomal fusion that enables the bacteria to survive intracellularly.Once inside the endosome, the elementary body becomes the larger reticulate body( 500 – 1000 nm) as a result of the glycogen produced.The reticular body is the reproductive form.It divides by binary fission approximately 2- 3 hours per generation.It does not contain a cell wall and is detected as an inclusion in the cell arranged as a mantle around the nucleus.The inclusion bodies are basophilic.They can also be stained with Lugol’s iodine because of the presence of the glycogen matrix.After division, the reticulate body returns to the elementary form and is released by exocytosis by the cell.A phagolysosome usually produces 100- 1000 elementary bodies. The whole process takes 24 – 48 hours. The EB can infect new cells and the cycle continues.
Antigenic structure of chlamydiae
Chlamydia antigen consists of 3 groups: genus- specific antigen, species specific protein antigen, serotype- specific. The serotype antigens are located on MOMP and are divided into many serovars or serotypes on the basis of this chlamydia.
How to isolate or culture chlamydiae
Chlamydiae can be isolated using the following methods:
Mice can be inoculated intranasally, intraperitoneally or intracerebrally. Mice die in 10 days. Smears made of lung, spleen, brain or peritoneal exudate show elementary bodies.
Organisms can be isolated by egg yolk inoculation of the specimen. Impression smears can be stained by Giemsa or Gimenez.
McCoy cells treated with cycloheximide are the most commonly used cell lines. Irradiated or metabolically inhibited cell lines can also be used for isolation of chlamydia. Inclusion bodies can be visualized by staining the cell lines.
What are the diseases caused by Chlamydia
Chlamydia trachomatis serotype A, B, Ba, C- is the world’s leading cause of preventable blindness( caused by a chlamydia infection called trachoma). Other diseases produced include conjunctivitis( serotype D to K) and ophthalmia neonatorum.
Chlamydia trachomatis is also the world’s leading cause of sexually transmitted diseases.It is associated with non- gonococcal urethritis and lymphogranuloma venereum( L1, L2, L3 serotype).Chlamydia trachomatis is one of the main causes of pelvic inflammatory disease( PID) and infertility in women
C. Pneumoniae causes pneumonia. Psittaci causes psittacose.
Laboratory diagnosis of chlamydia
Specimens should be collected by scraping the mucosa.Discharge should not be collected.Depending on the infection site, ocular, urethral, cervical, sputum, respiratory secretions can be collected.In suspected psittacosis, blood and sputum are collected for microscopy, culture and serum for serology.
Direct detection of antigen
Antigen detection is a rapid method of diagnosing chlamydial infection.Example includes
Chlamydia trachomatis inclusion bodies can be detected by staining with Lugol’s iodine. Iodine may be used because the inclusion bodies contain a glycogen matrix. The Giemsa, Castaneda, Machiavello and Gimenez methods are better and can be used to stain ocular, cervical or urethral specimens
Direct fluorescent antibody test detects major external membrane proteins. It is considered the method of choice
Antigen and antibodies may be detected by ELISA. Antigen detection is more specific than antimicrobial detection.
Mice, fertilized egg hen and tissue cultures can be used to isolate chlamydia. The clinical specimen can be inoculated in the yolk bag of 6 to 8 day old eggs. The preferred isolation method is irradiated or cycloheximide treated McCoy cell culture.
Polymerase chain reaction, ligase chain reaction, can be used to detect chlamydia
Treatment of Chlamydia infection
Sulfonamides and tetracycline are the drugs of choice. Azithromycin is the drug of choice for non- gonococcal urethritis.