Chlamydia

Chlamydia is small obligate intracellular parasite.

Although Chlamydia can synthesize most of their metabolic intermediates, it is unable to synthesize its own ATP. This may be a reason for Chlamydia to be a intracellular parasitic microbe.

Generally Chlamydia is considered to belong to bacteria.

Chlamydia has DNA, RNA and ribosomes. It proliferates by binary fission. It possesses an inner and outer membrane similar to Gram-negative bacteria.It has lipopolysaccharide but not peptidoglycan. It is sensitive to many antibiotics.

Chlamydia has two unique forms when it proliferates in host cells:

elementary body (EB)reticulate body (RB)

◇ EB: is smaller (0.25 to 0.3 µm in diameter), and has dense structure, and infectivity.

◇ RB: is larger (0.5 to 0.6 µm in diameter), and has loose structure, and no infectivity.

EB and RB

Chlamydia only has one genus with three species and all the species can cause human diseases:

•C. trachomatis: causes trachoma ( 沙眼 ), urogenital infections, conjunctivitis ( 结膜炎，红眼睛 ), pneumonia and lympho-granuloma venereum (LGV, 性病淋巴肉芽肿 ). Humans are the only natural host.

•C. pneumoniae: causes bronchitis, pneumonia and sinusitis. Humans are the only natural host.

•C. psittaci: causes pneumonia (psittacosis).

Developmental cycle

Staining methods

Gram-negative but Gram stain is not used for identification.

Giemsa stain is often used. EB is purple while RB is blue.

Staining methods

Immunofluorescence usin

g specific antibodies can sta

in the inclusion body brightl

y.

I. Chlamydia trachomatis

• Chlamydia trachomatis has 3 serotypes: trachoma, LGV and mouse pneumonia.

• According to the antigenic difference of MOMP (major outer membrane protein), C. trachomatis subsp. trachoma has 14 serotypes and C. trachomatis subsp. LGV has 4 serotypes.

• Chlamydia trachomatis has endotoxin-like substance and the MOMP can block the fusion of chlamydial endosome and cellular lysosome.

Among the 14 serotypes of

C. trachomatis subsp. trachoma: • 4 serotypes cause trachoma

– the first cause of blindness in the world – Transmitted by eye-hand-eye pattern through direct or i

ndirect (e.g., towel and toy) contact

• 12 serotypes cause inclusion conjunctivitis (e.g., swimming pool conjunctivitis) and non-gonococcal urethritis (NGU) – NGU is a common STD with or without clinical symptom

s

• 10 serotypes cause infant pneumonia

Chlamydia trachomatis subsp. LGV

◇ LGV serotype can cause lympho-granuloma venereum, a STD that is prevalent in Africa, Asia and South America.

◇ Occasionally, LGV serotype can cause conjunctivitis. ◇ Humans are the only natural host.

◇Culture is the most specific method. Specimens are inoculated to susceptible cells and then the infected cells are examined for the presence of inclusion bodies after staining. ◇Microscopy: directly examine in the sample smear.◇Serological examination: Due to its parasitic character, its specific antibody is usually low and do not distinguish between current and past infections. So serological examination is of little clinical importance. ◇ PCR and Southern hybridization.

Laboratory diagnosis

Treatment and prevention

◇ Tetracyclines and erythromycin are used for treatment.◇ No vaccine is practically used for prevention.

II. Chlamydia pneumoniae

◇ Chlamydia pneumoniae only has one serotype and named as TWARThe name comes from the combination of names of the two original isolates with the same serological examination results: strain TW-183 from Taiwan in 1965 and strain AR-39 from America in 1983.

◇ This microbe is transmitted person-to-person by respiratory droplets.◇ Chlamydia pneumoniae is the causative agent of atypical pneumonia.

◇ In addition, it can cause a pharyngitis, bronchitis and si

nusitis.

◇ Culture is difficult so the serological tests are most com

monly used. A four-fold rise in specific antibody titers in p

aired serum samples indicates the infection.

◇ Tetracycline and erythromycin are the choice of antibio

tics. No vaccine is available.

III. Chlamydia psittaci

◇ Chlamydia psittaci is firstly isolated from parrot. Later many birds are found to be able to carry the microbe. In birds, C. psittaci causes inapparent infection.

◇ C. psittaci can cause human disease called parrot fever (psittacosis) with fever, chill, cough and headache, which can develop into a mild pneumonia.

◇ Laboratory diagnosis is based on serological tests.

◇ Tetracycline or erythromycin are the choice of curative antibiotics. No vaccine is available.