They are Gram – negative eubacteria that are obligate intracellular parasites and that like Coxiella, have a life cycle that includes a resistant stage that mediates transmission. 

Chlmydia are obligate intracellular bacterial parasite of humans, animals and birds with tropism for squamous epithelial cells and macrophages of the respiratory and gastrointestinal tracts. 

They possess both DNA and RNA, have cell wall and ribosomes, they replicate by binary fission without an eclipse phase and are susceptible to the usual antibiotics and chemotherapeutic agents.

Chlamydias alternate between two distinct stages:

  • A small metabolically active, infectious form called the elementary body that is released by the infected host cell, and
  • A large non infectious, actively dividing form called the reticulate body that grows within the host cell vacuoles. This terminology was devised prior to the full realization of the bacterial nature of the chlamydias.

Elementary bodies are tiny, dense spheres shielded by a rigid, impervious envelope that ensures survival outside the eukaryotic host cell. Reticulate bodies are finely granulated and have thin cell walls.

To emphasize the homologous of cellular processes in the chlamydias and other bacteria, we shall call the actively growing cell (reticulate body) – vegetative cell and the infectious form (elementary body).


The chlamydiospores is small, with a rigid cell wall; they lack detectable metabolic activity. When it contacts a host cell, it includes phagocytosis by the host cell; the rest of the life cycle occurs within the phagosome.

Some component of the chlamydiospores inhibits the fusion of phagosome with lysosomes; presumably there are other changes in the phagosomes membrane that allow permeation by host metabolites needed by the parasite. The chlamydiospores enlarges; loses its rigidity, and begins macromolecular synthesis. Since the chlamydiospores enlarges; loses its rigidity, and begins macromolecular synthesis. 

Since the chlamydiospores is very low in RNA, particular rRNA, initial protein and RNA synthesis is probably devoted to increasing the number of ribosomes.

The genus Chlamydia contains four species: C. trachomatis; C. psittaci, C. pneumoniae which can affect humans, and the fourth species C. pecorum created recently to include some strains affecting ruminants.

Diseases of Chlamydia trachomatis

The reservoir of pathogenic strains of Clamydia trachomatis is the human body. The microbe shows astoundingly broad distribution within the population, often being carried with no symptoms. Elementary bodies are transmitted in infectious secretions, and although infection can occur in all age groups, disease is most severe in infants and children.

Chlamydias Disease of The Eye

The two forms of chlamydias eye disease, ocular trachoma and inclusion conjunctivitis, differ in their patterns of transmission and ecology. Ocular trachoma, an infection of the epithelial cells of the eye, is an ancient disease and a major cause of blindness in certain parts of the world.

The first signs of infectious are a mild conjunctival exudates and slight inflammation of the conjunctiva. This is followed by marked infiltration of lymphocytes and macrophages into the infected area.

Transmission is favored by contaminated fingers, fomites, flies, and a hot, dry climate.

Nihal Sharma

Assistant Editor

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