MICR 420

Emerging and Re-EmergingInfectious Diseases

Lecture 7:C. trachomatis

Dr. Nancy McQueen & Dr. Edith Porter

Overview C. trachomatis The genus Chlamydia

Morphology Growth and metabolic

characteristics Virulence factors Diseases Diagnosis

Direct antigen test Culture PCR Immune response

Therapy Threats:

Apparently under control

Chlamydia Obligate gram-negative intracellular bacteria

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 Small elementary bodies (EB)

Survives outside host cells Transferred to new host Similar in function to a spore

RNA:DNA = 1:1 Larger reticulate bodies (RB)

Grow within cells RNA:DNA = 3:1

Do not survive outside host

Elementary

Reticulate

Chlamydia Developmental Cycle

48h – 72h

Persistent Forms

EB attach to epithelial host cell Endocytosis Prevention of fusion with

lysosome Development into RB RB proliferation, formation of

large inclusion bodies Visible in light microscope

Development into EB Rupture of host cell and

release of EB

Chlamydia Species C. pneumoniae

World wide ~ 10% of pneumonias and 5% of all

bronchitis cases C. psittaci

Psittacosis Zoonotic pneumonia Inhalation of droppings from infected

birds Category B biological weapon

C. trachomatis Various serotypes

Eye infections STI

Inclusion conjunctivitis Transmitted to newborn's eyes during passage

through the birth canal Preventive erythromycin

Spread through swimming pool water Treated with tetracycline

Trachoma Greatest cause of blindness worldwide

Chlamydia Infection of the Eyes

Trachoma World wide ~ 80 (150?) million people infected and

~ 6 million blind 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%20Borne%20Diseases/Trachoma.jpg

Simplified WHO System to Assess Trachoma

(from Matthew J. Burton, British Medical Bulletin, 2007)

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

Pathogenesis of C. trachomatis

(A) Chlamydia elementary bodies (EB) translocate Tarp into an associated cell to orchestrate rearrangement of host cell actin. The C-terminal 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)

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 NFB signal transduction, a key pathway of the acute inflammatory and innate immune response.

Immune Response to C. trachomatis

Not well understood Infection controlled by cell mediated immune

response However: contributes also to the scarring

Antibodies are formed Tear IgG actually enhance uptake Tear IgA appear to be protective

(Matthew J. Burton, British Medical Bulletin, 2007)

Diagnosis of Trachoma No “gold standard” test Direct antigen test PCR ELISA to measure patient antibodies against outer

membrane proteins, conserved heat shock proteins Culture

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 Eyelid surgery Antibiotics to treat the infection

Tetracycline Azithromycin

Education about facial cleanliness and personal hygiene

Environmental improvements

WHO’s Global Alliance for the Elimination of Blinding Trachoma by

2020

Take Home Messages

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

http://www.who.int/topics/trachoma/en/ http://www.cdc.gov Textbooks

Microbiology: A clinical Approach (2010) Garland Science

Prescott’s Principles of Microbiology (2009) McGraw-Hill Microbiology: An Evolving Science (2009) Norton

Primary literature Betts et al., Current Opinion in Microbiology, 2009, 12:81–87 Matthew J. Burton, British Medical Bulletin, 2007