Introduction image

Chlamydia considers as the obligate parasites and sometimes refers as “Large viruses”. These are true bacteria and differ from the virus by many ways. Like bacteria, chlamydia also possesses both DNA and RNA. These multiply by binary fission, whereas viruses never do so.

Chlamydia possesses bacterial cell type incorporated with peptidoglycan probably containing mumaric acid. It also comprises of ribosomes, whereas viruses never do.

Content: Chlamydia

  1. Definition
  2. Features
  3. Uniqueness
  4. Taxonomy
  5. Life Cycle
  6. Pathogenicity
  7. Diagnosis
  8. Treatment
  9. Significance


Chlamydiae can define as the gram-negative bacteria that go through a complex life-cycle with different forms of intracellular multiplication. These are having a variety of metabolically active enzymes. Many antimicrobial drugs can inhibit their growth. Chlamydiae reproduce via binary fission, and complete their biphasic developmental cycle within 40-60 hours.


  • Gram reaction: These give negative gram reaction.
  • Motility: Chlamydiae are generally non-motile.
  • Shape: Chlamydiae are roughly spherical.
  • Size: It considers as one of the smallest prokaryotic organism whose size ranges between 0.2-1.5 µm.
  • Capsule: It is absent in chlamydia.
  • Cytoplasmic membrane: It lies under the cell wall and contains high lipid content.
  • Genome: The DNA appears as an irregular mass inside the cytoplasm without a nuclear membrane. Chlamydia possesses a genome size of 4-6X108 Daltons and 41-44% of G+C content.
  • Ribosomes: These are diffused structures in the cytoplasm.
  • Nature: These behave as an obligate intracellular parasite.
  • Reproduction: Chlamydia reproduces only in the cytoplasmic vesicles of the living cells of their host.
  • Chemical nature: These contain high lipid content, especially phospholipid.
  • Staining: Chlamydiae can be stained by Giemsa’s stain and Macchiavello’s stain.


Chlamydiae share some of the unique attributes that make it different from the other.

Energy parasite: Microbiologist considers Chlamydiae as “Energy parasite” because of the fact they lack ATP generating system of their own but can obtain ATP from the host cell.

Enzyme system: Chlamydiae comprise few enzymes for the synthesis of peptidoglycan. The chlamydial cell wall is devoid of peptidoglycan, but the enzymes involved in the synthesis of peptidoglycan accounts for the penicillin effect that disrupts peptidoglycan synthesis and inhibits chlamydial growth.

FtsZ gene: Chlamydia lack FtsZ gene, which is necessary for all the bacteria and archaea to form septum during the cell division.


Based on the pathogenicity and clinical symptoms, there are two ecological groups of chlamydia.

taxonomy of chlamydia

Group-A includes C. trachomatis that primarily cause trachoma, inclusion conjunctivitis, lymphogranuloma venerum in man only.
Group-B includes C. pneumonia and C. psittaci that mainly infects birds which can be transmitted to the men by causing zoonotic infections.

Life Cycle

Chlamydia possesses a very complex growth and multiplication cycle, where it goes through different phases. The growth, reproduction and maturation of chlamydia usually take 48 hours. Its life cycle exists between two morphologically distinct forms or cell types.

life cycle of chlamydia

Elementary body: It also refers as “Chlamydiospore”. These are the small, rigid-walled, infectious particles that remain alive after its release from the host cell.

Reticulate body: It also refers to as “Initial body” that appears larger, thin-walled, non-infectious particles that undergo cell division via binary fission.

PropertiesElementary bodyReticulate body
Size0.3 µ0.5-1.0 µ
RNA to DNA ratio1:13:1
RoleAdapted for extracellular survivalAdapted for intracellular growth
EndocytosisIt can induce endocytosisIt does not
Metabolic activityIt is metabolically inactiveIt is metabolically active

Stages of Growth and Multiplication

Chlamydia goes through a series of developmental stages that are given below:

Attachment: First, the small cell type (highly infectious) attaches to the cell surface of the host cell and enters inside it. Here, a small cell type is mainly known as “Elementary body”.

Ingestion: Then the elementary body is ingested by the host cell employing an endocytic process known as “Phagocytosis”.

Differentiation: After entering into a host cell, the elementary body will tend to retain its structural integrity inside the membrane-bound vesicles. During this stage, there is no eclipse (where a cell loses its infectious ability). In this stage, the small cell type or elementary body morphologically changes into a large cell type, and the cell now refers as a “Reticulate body”.

Cell division: The reticulate body continuously enlarges in size and multiplies by the repeated binary fission after (10-15 hours) of infection.

Differentiation: Then, the reticulate body tends to decrease in size and become a typical elementary body to complete the developmental cycle. It involves reorganization of the large cell types into small ones.

Cell lysis: The infected host cell undergo cell lysis after 42 hours of infection as a result of inclusion membrane rupture.

Host cell lysis: Finally, the host cell ruptures after 48 hours of infection and release elementary body, which may cause new disease in a healthy cell.


C. trachomatis predominantly affects the mucus membrane of the eye, a genitourinary tract of humans.
C. pneumonia and C. psittaci primarily infects the bird and can be transmitted to man where they can cause lung infection.


The diagnosis of a person infected by the chlamydia sp. involves the following serological tests:
Microimmunoflourescent test can be employed for the patient with an eye infection. The direct immunofluorescent test can be employed for the patients suffering from neonatal conjunctivitis and early trachoma. Frei test (type IV hypersensitivity test) used to kill organisms in the genitourinary tract.


The patients infected by C. trachomatis can be treated by the antibiotics (doxycycline or azithromycin). Doxycycline or azithromycin or erythromycin can be given to the patients infected by C. pneumonia, while doxycycline and erythromycin can be given to the patients infected by C. psittaci.

The diseaes caused by chamydiae are relatively easy to treat, but has two problems:

  • Latency of infection: The infection may remain latent or sub-clinical for years.
  • The susceptibility of the compromised host to reinfection.


These are only species of genus chlamydia are recognized, C trachomatis, C. psittaci and C. pneumonia. C trachomatis is the causative agent of two prevalent human diseases; the genitourinary tract disease (Lymphogranuloma venerum), and the conjunctivitis infection (trachoma).

C. psittaci causes “Psittacosis” disease in birds that occasionally transmit to human and causes pneumonia-like symptoms. C. pneumonia is the causal organism of a variety of respiratory syndromes in humans.

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