Transcript MICR420 S2010 Lec 7 CT - Cal State LA

MICR 420
Emerging and Re-Emerging
Infectious Diseases
Lecture 7:
C. trachomatis
Dr. Nancy McQueen & Dr. Edith Porter
Overview
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C. trachomatis
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The genus Chlamydia
Morphology
Growth and metabolic
characteristics
Virulence factors
Diseases
Diagnosis
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Direct antigen test
Culture
PCR
Immune response
Therapy
Threats:
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Apparently under control
Chlamydia
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Obligate gram-negative intracellular bacteria
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No peptidoglycan layer
Major outer membrane protein accounts for 60% of
all surface protein
Small genome (~1.0 Mb)
Depend on host molecules for replication
Limited or no ATP synthesis
Two forms exist
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Small elementary bodies (EB)
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Survives outside host cells
Transferred to new host
Similar in function to a spore
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RNA:DNA = 1:1
Larger reticulate bodies (RB)
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Grow within cells
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RNA:DNA = 3:1
Do not survive outside host
Reticulate
Elementary
Chlamydia Developmental Cycle
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EB attach to epithelial host cell
Endocytosis
Prevention of fusion with
lysosome
Development into RB
RB proliferation, formation of
large inclusion bodies
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48h – 72h
Visible in light microscope
Development into EB
Rupture of host cell and
release of EB
Persistent
Forms
Chlamydia Species
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C. pneumoniae
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C. psittaci
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World wide
~ 10% of pneumonias and 5% of all
bronchitis cases
Psittacosis
Zoonotic pneumonia
Inhalation of droppings from infected
birds
Category B biological weapon
C. trachomatis
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Various serotypes
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Eye infections
STI
Chlamydia Infection of the
Eyes
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Inclusion conjunctivitis
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Transmitted to newborn's eyes during passage
through the birth canal
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Spread through swimming pool water
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Preventive erythromycin
Treated with tetracycline
Trachoma
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Greatest cause of blindness worldwide
Trachoma
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World wide ~ 80 (150?) million people
infected and ~ 6 million blind
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Mostly in developing countries
3% of cause of all blindness world wide
Transmitted eye-hand-eye, eye-fomite-eye,
flies
Infection occurs usually during childhood
Chronic follicular conjunctivitis
inversion
of eyelashes
irritation of cornea
corneal ulcerations, scarring
vision loss
typically at age 30 – 40
Trachoma
Histopathology of Trachoma
http://www.lenntech.com/images/Water%2
0Borne%20Diseases/Trachoma.jpg
Simplified WHO System to
Assess Trachoma
Grade
Description
TF
Trachomatous inflammation—Follicular: The presence of
five or more follicles (>0.5 mm) in the upper tarsal
conjunctiva
TI
Trachomatous inflammation—Intense: Pronounced
inflammatory thickening of the tarsal conjunctiva that
obscures more than half of the deep normal vessels
TS
Trachomatous scarring: The presence of scarring in the
tarsal conjunctiva
TT
Trachomatous trichiasis: At least one lash rubs on the
eyeball
CO
Corneal opacity: Easily visible corneal opacity over the pupil
(from Matthew J. Burton, British Medical Bulletin, 2007)
Pathogenesis of C. trachomatis
(A) Chlamydia elementary bodies (EB) translocate Tarp into an associated cell to orchestrate rearrangement of host cell actin. The Cterminal domain of Tarp directly nucleates small actin filaments followed by hostmediated signaling involving tyrosine phosphorylation
(*P) cascades and ultimately Arp2/3 to mobilize actin assembly necessary for invasion. (B) Throughout development, chlamydial
inclusions intercept host-derived vesicles via recruitment of Rab GTPases (Rabs 1, 4, 10, and 11) and SNARE (Vamp 3, 7, and 8)
molecules through interactions with Inc proteins. (C) Established inclusions are able to interfere with NF-kB (p50 and RelA) activation
through ChlaDub1-mediated prevention of IkBa ubiquitination (*Ub) or CT441-mediated degradation of RelA. This would be predicted to
interfere with proinflammatory signals originating from ligand binding to TNF family (TNFR) or pattern recognition (PRR) receptors.
Virulence Factors of C. trachomatis (CT)
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Contribute to intracellular survival and proliferation
In part secreted via Type III secretion apparatus
Tarp (Translocated actin recruiting phosphoprotein):
effects actin rearrangement and endocytic uptake of
CT
CT inserts proteins (Inc and others) in inclusion
(endosome) membrane that prevent fusion of host
lysosomes
CT releases proteins (ChlaDub1, CT441) into the
cytoplasma that interfere with NFkB signal
transduction, a key pathway of the acute
inflammatory and innate immune response.
Immune Response to C.
trachomatis
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Not well understood
Infection controlled by cell mediated immune
response
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However: contributes also to the scarring
Antibodies are formed
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Tear IgG actually enhance uptake
Tear IgA appear to be protective
(Matthew J. Burton, British Medical Bulletin, 2007)
Diagnosis of Trachoma
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No “gold standard” test
Direct antigen test
PCR
ELISA to measure patient antibodies against
outer membrane proteins, conserved heat shock
proteins
Culture
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inoculating specimens onto cell culture monolayers
Visualization of inclusion bodies after 48 – 72 h using
fluorescent labeled monoclonal antibodies against CT
LPS or MOMP
Therapy and Prophylaxis of
Trachoma
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Eyelid surgery
Antibiotics to treat the infection
Tetracycline
WHO’s Global Alliance
 Azithromycin
for the Elimination of
 Education about
facial
Blinding
Trachoma by
2020
cleanliness and personal
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hygiene
Environmental improvements
Take Home Messages
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Chlamydia are obligate intracellular bacteria that have a
unique life cycle alternating between infectious
elementary bodies and proliferative reticulate bodies.
Pathogenic factors include rearrangement of
cytoskeleton promoting uptake, inhibition of fusion of
lysosomes with endosomes and inhibition of NfkB
activation.
C. trachomatis serotypes A-C (-K) cause trachoma, a
chronic conjunctivitis leading to blindness.
Trachoma is diagnosed by direct antigen and nucleic
acid based test and treated with tetracyline and
azithromycin.
Resources
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http://www.who.int/topics/trachoma/en/
http://www.cdc.gov
Textbooks
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Microbiology: A clinical Approach (2010) Garland
Science
Prescott’s Principles of Microbiology (2009) McGrawHill
Microbiology: An Evolving Science (2009) Norton
Primary literature
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Betts et al., Current Opinion in Microbiology, 2009, 12:81–87
Matthew J. Burton, British Medical Bulletin, 2007