Chlamydia: Types, Infection & Lifecycle

• Chlamydia are Gram-negative, non-motile, obligate aerobic bacteria.
• These bacteria are obligate intracellular.
• Chlamydia lacks a typical peptidoglycan layer in the rigid cell wall.
• The cell wall resembles that of Gram-negative bacteria but lacks muramic acid.
• Asymptomatic infections are a major factor in Chlamydia trachomatis transmission.
• Chlamydia trachomatis targets epithelial cells of the cervix and upper genital tract in women and the urethra and rectum in both men and women.
• Elementary bodies infect host cells and convert to non-infectious reticulate bodies.
• Reticulate bodies undergo binary division, resulting in numerous reticulate bodies that transition back into elementary bodies
• Infected cells eventually burst, releasing elementary bodies to infect other cells.

Chlamydia psittaci

• Causes psittacosis, infecting the lungs.
• Symptoms range from asymptomatic to high fever, cough, dyspnea, myalgia, headache, and pneumonia.
• Can disseminate to the liver (hepatomegaly, jaundice), heart (myocarditis, pericarditis), and nervous system (hearing loss, transverse myelitis, encephalitis).

Diagnosis

• Collect samples from the urethra and cervix for genitourinary infections and the conjunctiva for ocular diseases.
• Direct fluorescent antibody staining shows characteristic intracellular cytoplasmic inclusions.
• Gram stain of urethral discharge shows neutrophils, but no Gram-negative diplococci, suggesting chlamydia infection.
• Tissue culture in human cell lines can culture Chlamydia.
• Nucleic acid amplification tests (NAATs) are the test of choice.
• First voided urine or urethral discharge works for NAATs.
• Serologic testing is not useful for diagnosing Chlamydia trachomatis urogenital infections because it cannot differentiate between current or past infections.
• Antibody tests for Chlamydia psittaci and Chlamydia pneumoniae can be helpful.
• The site of replication appears as an inclusion body in the cytoplasm.
• Urinalysis may show pyuria with a negative Gram stain and culture.

Treatment

• Azithromycin is the drug of choice for Chlamydia trachomatis sexually transmitted diseases.
• Patients diagnosed with gonorrhea must also be treated for chlamydia trachomatis with azithromycin.
• Oral erythromycin is preferred for neonatal inclusion conjunctivitis and pneumonia.
• Doxycycline or tetracycline is the drug of choice for Chlamydia psittaci and lymphogranuloma venereum (LGV).
• Elementary bodies (EB) are the infectious, extracellular form.
• Reticulate bodies (RB) are the intracellular, metabolically active form.
• The reticulate body undergoes repeated cycles of binary fission, producing elementary bodies.
• Sexually transmitted diseases caused by Chlamydia trachomatis are common globally.
• It is the most common bacterial cause of sexually transmitted diseases in the U.S.
• Trachoma is most frequent in developing countries like North Africa.
• Trachoma is a leading cause of blindness in those regions.
• Chlamydia pneumoniae transmits person-to-person by aerosol.
• Trachoma transmits via finger-to-eye or eye-to-eye contact.
• Chlamydia psittaci infects birds, and humans contract it by inhaling aerosolized organisms, usually from dried bird feces.
• Chlamydia trachomatis divides into 15 serotypes.
• Serotypes A-C cause trachoma, a chronic eye infection that often results in blindness due to permanent opacities of the corea and distortion of eyelids.
• Serotypes D-K cause genital infections, like chlamydia.
• Serotypes L1-L3 cause lymphogranuloma venereum (LGV).

Chlamydia trachomatis: Male Symptoms

• A common cause of non-gonococcal urethritis, characterized by dysuria and watery, non-purulent urethral discharge.
• Urethral discharge is typically white, gray, or sometimes clear, only evident after penile “stripping” or during morning hours.
• Infection may progress to epididymitis, prostatitis, or proctitis.

Chlamydia trachomatis: Female Symptoms

• About 70% are asymptomatic or have mild symptoms such as vaginal discharge, bleeding, abdominal pain, and dysuria.
• A minority of women will have mucopurulent discharge with easily induced endocervical bleeding.
• Some women may experience postcoital or intermenstrual bleeding.
• It can present as dysuria and be mistaken for a urinary tract infection (UTI).

Infant Symptoms

• Infant pneumonia presents with rhinitis followed by a distinct staccato cough with the child remaining afebrile.
• It can also cause neonatal conjunctivitis (ophthalmia neonatorum) characterized by eyelids swelling, hyperemia, and copious purulent discharge, conjunctival scarring, and corneal vascularization.

Lymphogranuloma Venereum (LGV)

• Primary stage: Occurs 3-30 days after exposure with a painless genital ulcer or papule (1-6 mm). Sores can also be present in the mouth or throat.
• Secondary stage: Development of unilateral or bilateral inguinal or femoral lymphadenopathy, and an anal syndrome with proctitis or proctocolitis.
• Late stage: Occurs if untreated, characterized by necrosis and rupture of lymph nodes, anal-genital fibrosis, anal fistula, and genital elephantiasis.
• Chlamydia pneumoniae causes upper and lower respiratory tract infections, especially bronchitis and pneumonia.
• Infections are usually mild or asymptomatic, resembling other atypical pneumonias.
• Chlamydia pneumoniae infects primarily the lungs, causing high fever and pneumonia, and can also cause extrapulmonary infections.
• Chlamydia pneumoniae causes atypical pneumonia.
• Chlamydia trachomatis also causes trachoma (keratoconjunctivitis), nongonococcal urethritis (dysuria and urethral discharge), neonatal conjunctivitis (ophthalmia neonatorum), and adult inclusion conjunctivitis.