Chlamydia & Rickettsia
MLAB 2434: Microbiology
Keri 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.