Chlamydia Bacteria Overview

Study Notes

Chlamydia are Gram-negative, non-motile bacteria, coccoid in shape, and very small, usually around 350nm in diameter.
They have a peptidoglycan-free cell wall.
They require a host cell for energy production; they lack cytochromes and flavoproteins.
They have a unique developmental cycle with two forms: an elementary body (EB) that is metabolically inactive and infectious, and a reticular body (RB) that is metabolically active and non-infectious.

Primarily infects humans.
Divided into biovars (trachoma, lymphogranuloma venereum) and serovars based on MOMP proteins.
Specific serovars are associated with specific diseases.
Biovar A, B, Ba, C cause trachoma.
Biovar D-K cause urogenital tract disease.
Biovar L1, L2, L2a, L2b, L3 cause lymphogranuloma venereum.

Lack of peptidoglycan in their cell wall makes them resistant to some antimicrobials (e.g., beta-lactams).
Outer membrane contains LPS and MOMP proteins (major outer membrane proteins). MOMP proteins are species and type-specific antigens, and the antibody against them can neutralize the pathogen. Chlamydia are distinguished by antigenic differences in MOMP protein sequences.

The life cycle alternates between elementary bodies (EB) and reticular bodies (RB).
EBs are infectious, and they attach to host cells.
Inside the host cells, EBs develop into RBs.
RBs multiply and differentiate back into new EBs.
This process results in the formation of inclusions inside the host cells.

Trachoma: Chronic keratoconjunctivitis, causing scarring and the eyelids turning inward (entropion), leading to corneal abrasion and vision loss.
Urogenital Tract Infection: Urethritis in men (urethral discharge or dysuria), cervicitis, endometritis in women, and can lead to chronic pelvic inflammatory disease (PID), causing fertility problems.
Lymphogranuloma Venereum (LGV): Primary lesion appears at the site of infection on genitals, causing inflammation and swelling of the lymph nodes, particularly inguinal lymph nodes.

Culture: HeLa cells are used to cultivate Chlamydia to identify their antigen using immunological methods.
Nucleic Acid-Based Tests (PCR): Detect chlamydia genomes for diagnosis using samples like urine or genital swabs.
Serology: Detect antibodies (IgM, IgG, IgA) in serum samples by ELISA.

Chlamydia are not susceptible to drugs acting on peptidoglycan synthesis, such as beta-lactams.
First-line treatment includes antibiotics that target protein synthesis (e.g., macrolides and tetracyclines).
No vaccines are available. Common recommended regimens include: Azithromycin 1 gram orally in a single dose or Doxycycline 100 mg orally twice a day for 7 days.