Chlamydia - Classification, Morphology, Pathogenesis, Medically Important Species
Classification of Chlamydia
On the basis of phenotypic characteristics, Chlamydia can be classified as:
Domain: Bacteria
Phylum: Chlamydiota
Class: Chlamydiia
Order: Chlamydiales
Family: Chlamydiaceae
Genus: Chlamydia
Introduction to Chlamydia
The Chlamydia genus contains one of the most common pathogens associated with STI. i.e. Chlamydia trachomatis. They are obligate intracellular parasites with an affinity for squamous epithelial cells of GI and RT.
The genus-specific LPS is present in the cell wall which can be detected by Complement Fixation Test (CFT). The species-specific and strain-specific major outer membrane protein (MOMP). On the basis of MOMP, 18 different serovars were associated with different primary clinical syndromes.
C. trachomatis also associated with infertility, and ectopic pregnancy, sometimes they are asymptomatic- resulting in inadvertent transmission. It occurs in two morphology/different forms:
Elementary form (EB)
Reticulate body (RB)
Morphology, Forms of Chlamydia
The morphology of Chlamydia exists in two forms:
Elementary form (EB)
Reticulate body (RB)
Elementary form (EB)
Elementary form (EB) is a small, round, extracellular, infective form
measures 300-400 nm in size
do not multiply in EB form but are infectious
cause infection by binding to receptors on the epithelial cells and stimulate uptake of bacteria by infiltration
Reticulate body (RB)
Reticulate body (RB) is large, 500-1000nm in size, non-infectious form
metabolically active, replicating form
Pathogenesis of Chlamydia
Elementary form (EB) cells of Chlamydia attach to microvilli of susceptible epithelial cells followed by penetration into the host cell. Inside host cells, EB remains within the cytoplasmic phagosomes in which EBs begin to multiply.
The formation of phagolysosomes is prevented. Thus, the intracellular killing of EB is inhibited. Within 6-8 hours, EBs are transformed into metabolically active reticulate bodies (RB).
RBs of Chlamydia multiply by binary fission, which continues for 12-24 hours. The RBs then revert to EB. The developing phagosome with accumulated reticulate bodies within the host cell is called the inclusion body. The mature inclusion body contains nearly 100-500 EBs which are released when the host cell ruptures and are marked by the presence of a scar which is one of the pathological changes in the infection.
Medically important species
Some medically important Chlamydia species includes:
Chlamydia trachomatis
Chlamydia pneumoniae
Chlamydia psittaci
Chlamydia abortus