A complete overview of the genus Chlamydia, its classification, and key species (Chlamydia trachomatis, Chlamydia pneumoniae, etc.), emphasizing its unique features as an obligate intracellular bacterium.
Explore the mechanisms of Chlamydia infection, including how it invades host cells, evades ...
Chlamydiaceae/Rickettsiae (1)
• Both pathogens can survive and reproduce at the hostile environment (extreme conditions)
Chlamydiaceae: Phylogeny
Family which once included 2 genera, Chlamydia and Chlamydophila
Single genus: Chlamydia
Egs:
- C.trachomatis, ocular, genital
- C.psittaci: psittacosis (affect the lungs and may cause inflammatory illness of the lungs
(pneumonia))
- C.pneumoniae (10-20% CAP, cardiovascular disease)
• One can get infected by chlamydia through non-sexual contact as well as sexual contact.
Psittacosis—also known as parrot fever, is a zoonotic infectious disease in humans caused by a
bacterium called Chlamydia psittaci and contracted from infected parrots, such as macaws,
cockatiels and even from other birds with poor hygiene.
• Chlamydia psittaci which has different serotype to the sexually transmitted chlamydia, and this
can be transmitted from flies and parasites.
• You can also get chlamydia transmitted through swimming pools too, although it is quite rare.
Majority of koala bears carry chlamydia species.
Chlamydia is elementary
These bacteria are obligate intracellular pathogens, meaning that they require host cell to survive
intracellularly and complete their life cycle. Chlamydia were first described by Sir Samuel Bedson
(1886-1969), he was studying a human cell that was infected with chlamydia psittaci. He noted two
different forms of the bacteria.
One being small elementary body which then changed into a large form. He believed it to be a virus.
But it was a bacteria.
Chlamydial Morphologies
C. pneumoniae growth consists of two alternating forms: elementary and reticulate bodies.
Elementary bodies (EB):
This is the electro dense, infectious form of chlamydia and it can be taken up by the host endothelial
cell. Elementary bodies are metabolically inactive. They infect the host when cells ingest the
elementary bodies through the process of receptor-mediated endocytosis.
○ Infectious form (highly/resistant)
○ Electro-dense nucleoid (Hc1 histone)
○ Granular cytoplasm
○ Spherical, about 0.2-0.3 micrometre in diameter
○ Metabolically inactive
Reticular bodies (RB):
○ Non-infectious
○ Metabolically active
○ Intracellular reproductive form
○ Chromatin is dispersed due to transcription
○ About 0.5 to 2.0 micrometre in diameter
○ Has the ability to split by binary fission resulting in new RBs
Once inside the cell, the elementary bodies differentiate into reticulate bodies, which are
metabolically active but non-infectious. The reticulate bodies rely on the host cell for adenosine
triphosphate (ATP) synthesis. The reticulate bodies divide by binary fission and induce a host
Chlamydia Page 1
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