Chlamydiae Classification and Overview

Chlamydiae Classification

• Chlamydia are obligate intracellular pathogens
• They are classified as:
  • Phylum: Chlamydiae
  • Class: Chlamydiae
  • Order: Chlamydiales
  • Family: Chlamydiaceae
  • Genus: Chlamydia
  • Species: C. trachomatis, C. psittaci, C. pneumoniae

Chlamydia Overview

• Chlamydia are small, round to oval bacteria
• They were initially thought to be large viruses
• They possess a cell wall lacking peptidoglycan, similar to Gram-negative bacteria.
• They contain both RNA and DNA.
• They are susceptible to some antibacterial agents such as tetracyclines and erythromycin.
• Chlamydia lack the necessary energy machinery for independent existence.
• They cannot synthesize ATP or oxidize NADH.
• They reproduce through a replicative cycle, followed by binary fission.
• They are highly infectious and many species produce heat-labile toxins.

Chlamydia Morphology and Life Cycle

• Chlamydia exist in two forms:
  • Elementary bodies (EB): Extracellular, infectious, invasive stage, metabolically inert. They enter the body through endocytosis, a process similar to phagocytosis.
  • Reticulate bodies (RB) or initial bodies (IB): Intracellular, non-infectious, metabolically active. When EB undergo a transformation, they reorganize into RB which are less dense. They obtain energy (ATP) from the host cell and this transformation takes approximately 24-72 hours. RB undergo binary fission within the host cell's intracytoplasmic vacuole/phagosome. Host cell rupture releases daughter EB, allowing the infection to spread.

Chlamydia Species

• The three main species of Chlamydia can be distinguished by several parameters:
  • C. psittaci: Contains glycogen in intracytoplasmic inclusion body, sensitive to sulfonamide. Causes psittacosis in birds and humans.
  • C. trachomatis: Lack glycogen in intracytoplasmic inclusion body, resistant to sulfonamide. Causes trachoma, inclusion conjunctivitis, and various genital infections.
  • C. pneumoniae: Lack glycogen in intracytoplasmic inclusion body, resistant to sulfonamide. Causes atypical pneumonia, bronchitis, and sinusitis.

Chlamydia trachomatis Infections

• Ocular Infections:

  • Trachoma: Caused by serotypes A, B, and C. It is a chronic keratoconjunctivitis that is a leading cause of preventable blindness globally. Transmission occurs through direct contact, indirect contact via fomites, and during childbirth.
  • Inclusion Conjunctivitis: Caused by serotypes D-K. It is an acute suppurative disease of the conjunctiva. Occurs in infants and adults and has an incubation period of 2-5 days. Transmission is by direct or indirect contact.

• Genital Infections: Caused by serotypes D-K. It is a common cause of sexually transmitted infections (STIs) worldwide.

  • Non-gonococcal urethritis (NGU) is common, particularly among young adults.
  • Other genital infections include cervicitis, epididymitis, salpingitis, endometritis, pelvic inflammatory disease (PID), proctitis, pharyngitis, and Reiter's syndrome.
  • Chlamydial infections can lead to infertility and sterility.

Chlamydia psittaci Infections

• Pathogen: Primarily infects birds, particularly psittacine birds (e.g., parrots), and other avian species.
• Transmission: Humans get infected by inhaling bacteria from infected bird droppings.
• Disease: It causes psittacosis (ornithosis) in humans, a zoonotic disease of the lower respiratory tract. Symptoms range from mild to severe pneumonia and meningo-pneumonitis.

Chlamydia pneumoniae Infections

• Prevalence: Highly common worldwide, with 30-50% of the population having antibodies to C. pneumoniae.
• Transmission: Spread through airborne transmission. No known animal reservoir.
• Disease: Most infections are asymptomatic. It can cause upper and lower respiratory tract infections (URTI and LRTI), including atypical pneumonia, bronchitis, sinusitis, and pharyngitis. It can also exacerbate asthma.

Chlamydia Diagnosis

• Clinical diagnosis: Based on patient history and clinical symptoms.
• Laboratory diagnosis:
  • Specimens: Post-voidal urine, urethral swab, endometrial scraping, culdocentesis, conjunctival scraping, posterior nasopharyngeal swab, tracheal/bronchial aspirates.
  • Methods:
    • Urine tests: Detect C. trachomatis genes, results in 24 hours.
    • Culture: In McCoy cells,takes 3 days or more. Requires expertise and experience.
    • DFA test: Direct fluorescent antibody test.
    • Enzyme immunoassay:

Chlamydia Treatment and Prevention

• Treatment: Early detection and treatment are crucial.
  • Antibiotics: Tetracycline, doxycycline, minocycline, erythromycin, and azithromycin.
• Complications: HIV/AIDS, PID, subfertility, infertility.
• Prevention and Control:
  • Prophylactic treatment: Use of prophylactic ophthalmic eye drops for newborns, oral tetracycline or sulfonamides.
  • Hygiene: Personal and family hygiene.
  • Trachoma clinics: Establishment of dedicated clinics in endemic areas.

Lymphogranuloma Venereum (LGV)

• Caused by: Unique serovars of Chlamydia trachomatis (L1, L2, L3). These serovars differ from those causing urethritis, cervicitis, and proctitis (D-K).
• Presentation: Varies depending on the site of infection.
• Incubation period: 3 days to 1 month after exposure.
• Progression: It is an invasive, systemic infection that progresses in three stages:
  • Primary (Ulcer) stage: Painless vesiculo-papular ulceration at the site of inoculation, resembling a herpes lesion. Ulcer heals on its own in a few days.
  • Secondary stage: Developing weeks to months later, symptoms include inguinal lymphadenopathy, buboes, and fever. Buboes can become fluctuant and drain.
  • Tertiary stage: May occur months to years later, characterized by inflammatory strictures in the rectum, urethra, or vagina.

Dive into the fascinating world of Chlamydia with this quiz. Learn about their classification, morphological characteristics, and unique life cycle. Understand their role as obligate intracellular pathogens and their significance in infectious diseases.