Chlamydia Origin and Evolution

Recent phylogenetic studies have shown that Chlamydia and cyanobacteria, the community that includes the endosymbiont ancestor to modern plants' chloroplasts, have a shared ancestor. As a result, Chlamydia maintains unusual plant-like characteristics, both genetically and physiologically. The enzyme L, L-diaminopimelate aminotransferase, which is involved in plant lysine processing, is also involved in the formation of chlamydial cell walls. Plants, cyanobacteria, and Chlamydia all have remarkably similar genetic encoding for enzymes, indicating a nearly shared ancestor.

What is the Chlamydia Causative Agent?

The bacterium Chlamydia trachomatis is the chlamydia causative agent, which is a sexually transmitted infection. The majority of people who are infected show no signs or symptoms. When signs do emerge, they can appear just a few weeks after infection; the incubation period between exposure and the ability to infect others is estimated to be two to six weeks.

Chlamydia Classification

  • Domain: Bacteria

  • Phylum: Chlamydiae

  • Class: Chlamydiae

  • Order: Chlamydiales

  • Family: Chlamydiaceae

  • Genus: Chlamydia

Chlamydiae were once thought to be viruses because of their reliance on host biosynthetic machinery; however, they have a cell wall and contain DNA, RNA, and ribosomes, so they are now known as bacteria that causes chlamydia. Chlamydia is the only genus in the group (order: Chlamydiales, class: Chlamydiaceae). The species C. trachomatis and C. psittaci belong to the chlamydia genus, as does a new organism, the TWAR organism, which was recently proposed as a third species (C. pneumoniae). Human disease is caused by all three animals. Chlamydia psittaci infects a wide range of birds and rodents, while Chlamydia trachomatis is primarily found in humans.

Chlamydia Organism Developmental Cycle

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An elementary body and a reticulate body are two forms of Chlamydia bacteria. The nonreplicating infectious particle produced when infected cells rupture is known as the elementary body. It is similar to a spore and is responsible for the bacteria's ability to spread from person to person. The diameter of the elementary body can range from 0.25 to 0.30 m. A rigid cell wall protects this type (hence the combining form chlamyd- in the genus name). When exposed to target cells, the elementary body causes its own endocytosis. Typically, one phagolysosome creates 100–1000 elementary bodies.


Chlamydia may also take the form of a reticulate body, which is an intracytoplasmic form that plays an important role in the bacteria's replication and development. The reticulate body is significantly larger than the elementary body, with a maximum diameter of 0.6 m and a minimum diameter of 0.5 m. It is devoid of a cell wall. Reticulate bodies behave as inclusions in the cell when stained with iodine. The reticulate body stores the DNA genome, proteins, and ribosomes. This happens as a part of the bacteria's growth cycle. The reticular body is the structure where the chlamydial genome is translated into RNA, proteins are synthesised, and DNA is replicated.


The fusion lasts about three hours, with a 21-day incubation period possible. The reticulate body reverts to its elementary form after division and is released by the cell through exocytosis.


The infectious elementary body (EB) grows into a noninfectious reticulate body (RB) inside a cytoplasmic vacuole in the infected cell, according to studies on the growth cycle of Chlamydia trachomatis and Chlamydia psittaci in cell cultures in vitro. After the infectious particle enters the infected cell, there is a 20-hour eclipse period during which the infectious particle transforms into a reticulate body. After 36 to 50 hours after infection, the yield of chlamydial elementary bodies reaches its peak.


HctA and HctB, two histone-like proteins, play a part in regulating the differentiation of the two cell types. Until late RB to EB re-differentiation, the expression of HctA is tightly regulated and repressed by IhtA, a small non-coding RNA. Across Chlamydia species, the IhtA RNA is conserved.

Chlamydia Genus Symptoms and Pathology

Chlamydia genus symptoms: The majority of chlamydial infections are asymptomatic. Men, on the other hand, are more likely to experience a burning sensation while urinating. Odour and itching are two potential symptoms for women. As the infection progresses, both sexes may experience increased sebum development, which results in greasy sweat, an oilier skin, and can be misdiagnosed as acne eruptions rather than the body's secret battle to protect itself from an STD. Anyone who has had sexual contact with a possibly infected person could be given one of many tests to diagnose the disease.


Culture tests and nonculture tests can also be used to diagnose Chlamydia. Fluorescent monoclonal antibody tests, enzyme immunoassays, DNA probes, rapid Chlamydia tests, and leukocyte esterase tests are the most popular nonculture tests. The first test detects the main outer membrane protein (MOMP), while the second detects a coloured substance that has been transformed by an enzyme-linked to an antibody. Antibodies against the MOMP are used in rapid Chlamydia tests, while enzymes released by leukocytes containing the bacteria in the urine are detected in leukocyte esterase tests.

Chlamydia Bacteria Diseases

  • Ocular Infections: Trachoma and inclusion conjunctivitis are caused by Chlamydia trachomatis. The growth of follicles and inflamed conjunctivae are hallmarks of trachoma. Repeated infections can cause the cornea to become cloudy and vascularized, resulting in blindness. Inclusion conjunctivitis is a less severe inflammatory conjunctivitis that produces a purulent discharge.

  • Genital Infections: Nongonococcal urethritis in men and acute salpingitis and cervicitis in women are both infections caused by C trachomatis strains. Other strains cause lymphogranuloma venereum, a venereal disease characterised by genital lesions and involvement of regional lymph nodes (buboes).

  • Respiratory Infections: Psittacosis is an influenza-like illness caused by Chlamydia psittaci. In humans, Chlamydia pneumoniae (the TWAR organism) causes atypical pneumonitis.

Chlamydia Examples of Signs and Symptoms

  1. Genital Diseases 

    1. Women - 

      1. Chlamydial infection of the cervix (womb's neck) is a sexually transmitted infection that affects about 70% of women without causing any symptoms. The infection is spread through vaginal, anal, or oral sex. About half of those that have an asymptomatic infection that goes unnoticed by their doctor will experience pelvic inflammatory disease (PID), a term for infection of the uterus, fallopian tubes, and/or ovaries. 

      2. PID can cause scarring of the reproductive organs, which can lead to serious complications such as constant pelvic pain, inability to conceive, ectopic (tubal) pregnancy, and other severe pregnancy complications.

      3. Abnormal vaginal bleeding or discharge, stomach pain, painful sexual intercourse, fever, painful urination, or the need to urinate more often than usual are some of the signs and symptoms (urinary urgency). Screening is recommended for sexually active women who are not pregnant, particularly those under the age of 25 and those who are at risk of infection. 

      4. A history of chlamydial infection or another sexually transmitted infection, new or multiple sexual partners, and inconsistent condom usage are all risk factors. 

    2. Men -

      1. In around half of all cases, men with a chlamydial infection experience signs of infectious urethral inflammation. A painful or burning feeling when urinating, an irregular discharge from the penis, testicular pain or swelling, or a fever are all possible symptoms. 

      2. Chlamydia in men can spread to the testicles, causing epididymitis, which can lead to sterility in extreme cases if not treated. Chlamydia can also cause prostatic inflammation in men, but the exact role it plays in prostatitis is difficult to determine due to urethritis contamination.

  2. Eye Diseases

Chlamydia trachomatis causes trachoma, a chronic conjunctivitis. Fingers, mutual towels or cloths, coughing and sneezing, and eye-seeking flies may all spread the infection from one eye to the next. Mucopurulent ocular discharge, itching, redness, and lid swelling are all symptoms. Childbirth can also cause chlamydia eye infection in newborns. 

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  1. Joints

In young men, chlamydia can cause reactive arthritis (the triad of arthritis, conjunctivitis, and urethral inflammation).  It can affect both men and women, but it is more common in men.

  1. Infants

Half of all children born to chlamydia-positive mothers would be infected with the disease. Chlamydia can cause spontaneous abortion, premature birth, conjunctivitis, which can cause blindness, and pneumonia in children. When compared to chemical causes (within hours) or gonorrhoea (2–5 days), conjunctivitis caused by chlamydia usually occurs one week after birth.

Chlamydia Diagnosis

The polymerase chain reaction (PCR), transcription-mediated amplification (TMA), and DNA strand displacement amplification (SDA) are now the mainstays of nucleic acid amplification studies (NAAT). NAAT for chlamydia may be done on swabs taken from the cervix (women) or the urethra (men), self-collected vaginal swabs, or voided urine. Regardless of whether a cervical swab or a urine specimen is used, NAAT has been estimated to have a sensitivity of around 90% and a specificity of around 99%.

Chlamydia Treatment

Antibiotics can effectively treat C. trachomatis infection. Azithromycin, doxycycline, erythromycin, levofloxacin, or ofloxacin are recommended by the guidelines. Doxycycline (100 mg twice a day for 7 days) is possibly more effective in men than azithromycin (1 g single dose), but evidence for antibiotics' relative efficacy in women is sketchy. Erythromycin or amoxicillin are two antibiotics that are prescribed during pregnancy.


Patient-delivered partner therapy (PDT or PDPT) is a treatment choice for sexual partners of those with chlamydia or gonorrhoea. It is the method of treating the sex partners of index cases by giving the patient prescriptions or medications to provide to his or her partner without the health care provider first testing the partner.

FAQs (Frequently Asked Questions)

1. How Does Chlamydia Spread? What Is Chlamydiasis Causative Agent?

Ans) If you have vaginal, anal, or oral sex with someone who has chlamydia, you will get chlamydia. And if your sex partner does not ejaculate, you will still contract chlamydia. Even if you've already been infected with chlamydia and received treatment, you can become infected again. The chlamydiasis causative agent is usually C. trachomatis bacterium in humans.

2. What are the Early Signs of a Chlamydia Infection?

Ans) Some common signs of chlamydia infection are; Vaginal discharge that is abnormal, yellowish or has a strong odour. Swelling in the vaginal area/painful sex; When you pee, you can experience pain or a burning sensation. The need to pee more often than normal.