Chlamydia & Rickettsia

MLAB 2434: MicrobiologyKeri Brophy-Martinez

General Characteristics

• Obligate intracellular organisms• Can not be cultured on agar plates• Dependant on a host for survival

Chlamydia Characteristics

• Unique growth cycle because they are deficient in independent energy metabolism

• Replication involves elementary body (EB) and reticulate body (RB)– EB’s are infectious and non-

metabolically acitve– RB’s are noninfectious and

metabolically active

Life Cycle of Chlamydia

Chlamydia pneumoniae

• Important respiratory pathogen (acute respiratory disease, pneumonia, and pharyngitis)

• Common (50% of adults have antibodies)

• College age students most susceptible

• Implicated in asthma• Risk factor for Guillain-Barre’ syndrome

Chlamydia pneumoniae (cont’d)

• Reinfection common• Biphasic clinical picture–Prolonged sore throat and

hoarseness, followed by flu-like lower respiratory symptoms–Pneumonia and bronchitis

Chlamydia trachomatis

• Most commonly sexually transmitted bacterial pathogen in U.S.– Only HPV is a more commonly sexually

transmitted disease–Major cause of sterility in U.S.–May be transmitted to newborns during

delivery• Results in conjunctivitis

Chlamydia trachomatis (cont’d)

• Other sites of infection– Trachoma – infection of the conjunctiva,

resulting in scarring and blindness (Mostly in India and Egypt)

– Lymphogranuloma venereum• Infects lymph nodes• STD found in immigrants from the tropics

Chlamydia psittaci

• Causes psittacosis (parrot fever)• Identification based on history of

close contact with birds and serologic evaluation

Laboratory Diagnosis

• If cultured, must be in cells • Direct microscopic examination to find

EB’s– visualized with fluorescein-conjugated

antibodies

• Enzyme immunoassay• Nucleic acid probes with and without

amplification (PCR)• Serologic tests are method of choice for

detection (Four-fold rise in titer)

Rickettsia

• Intracellular, gram negative organism

• Requires host to replicate and survive

• Cause febrile illness through the bite of an arthropod

• Patient often presents with a rash• Posses a cell wall

Rickettsia and Related Organisms

Disease Agent Arthropod Vector

Rocky Mountain spotted fever

Rickettsia rickettsii Wood tick

Rickettsial pox Rickettsia akari House mouse mites

Murine typhus Rickettsia typhii Rat flea

Epidemic typhus Rickettsia prowazekii Human body louse

Scrub typhus Orientia tsutsugamushi Chigger mites

Ehrlichiosis Ehrlichia chaffeenis Lone star tick

Q fever Coxiella burnetti None- spead by inhalation

Laboratory Diagnosis of Rickettsial Disease

• Immunohistochemical detection• Serological tests• PCR

References

• Kiser, K. M., Payne, W. C., & Taff, T. A. (2011). Clinical Laboratory Microbiology: A Practical Approach . Upper Saddle River, NJ: Pearson Education.

• Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.