Mycobacteria tuberculosis Flashcards
Biology?
- Obligate Aerobic bacilli
- Acid-fast bacteria (red)
- Mycolic acid cell wall
- very fastidious
how does M. tuberculosis appear in a sputum smear stained with the Ziehl-Neelsen stain?
bright red bacilli
what is mycobacterias wall made of?
Mycolic acid & Lipid-Rich Wall
M. tuberculosis can be cultured on what medium?
Lowenstein-Jensen (LJ) Media (Typical small, buff coloured colonies of)
Transmission?
Human-to-human aerosol
when is there High mortality with Mycobacteria tuberculosis?
HIV co-infection
what are the virulence factors?
Mycolic acids
Cord factor
Lipoarabinomannan (LAM)
Mycolic acids are responsible for what?
protects against free radicals
prevents complement activation.
what will Cord factor do?
Prevents phagosome fusion with lysosome
what will Lipoarabinomannan (LAM) do?
Inhibits macrophage activation and prevents phagosome fusion
what are the minor virulence factors?
Superoxide Dismutase & Catalase
PDIM
19 kDa lipoprotein
Superoxide Dismutase & Catalase does what?
Neutralizes ROS (Reactive Oxygen Species) inside macrophages
PDIM does what?
Helps multi-cellular macrophage fusion (Giant Cell)
19 kDa lipoprotein does what?
Suppresses pro-inflammatory cytokines
Pathogenesis?
Primary infection:
- tuberculosis are engulfed by alveolar macrophages (survive and multiply). Non-resident macrophages attracted.
- fusion of macrophages to form Langhans giant cells.
- If bacterial load is high, dendritic cells transport Mtb antigens via lymphatics to hilar lymph nodes.
- Cell Mediated Immune (CMI*) Response is stimulated.
- Th1 cells migrate to lungs to activate uninfected macrophages and surround the infected macrophages and free bacteria via granuloma formation.
what leads to formation of “tubercles/granulomas” which encase live Mycobacteria tb and prevent further disease progression?
CMI
how do Large granuloma, associated with disease look like?
Necrotic caseous core with fibrin and liquid
what If host immune response is weakened at a later point in time (ex. AIDS)?
cavitation, or bursting of contained Mtb in granuloma, will occur, causing re-activated Tuberculosis disease.
what are the symptoms of Primary Tuberculosis?
usually asymptomatic
Produces a calcified granuloma or area of scar tissue
(May be a origin for reactivation or Secondary TB)
** Progressive Primary TB may be symptomatic**
what is Pulmonary Tuberculosis?
Persistent cough with mucous; sometimes with blood
- Chest pain
- Dyspnea
- Weight loss
Primary tuberculosis Occurs in what individuals?
individuals lacking previous contact with tubercle bacilli
what is seen in the Sub-pleural location in pulmonary TB?
Ghon focus (granuloma): 1-1.5 cm gray white area of caseous necrosis in sub-pleural location.
(Tubercle bacilli then drain to the regional lymph nodes)
what is the Ghon complex?
combination of Ghon focus and Hilar lymph node involvement
what symptoms are seen in Chronic state Pulmonary tuberculosis?
Fibrosis, scaring
Calcification
Persist for life
Show up as radio-opaque nodules
identify?
ghon complex
identify
ghon focus
what is secondary TB?
- Reactivation of dormant Mtb,
- Original granuloma bursts or cavitates
- Usually at the apex of the lung
- Frequently, its a consequence of impaired immunity
- Involves one or both apices in upper lobes (Ventilation (oxygenation) is greater in upper lobes)
Clinical findings of secondary TB?
Cough, Fever, drenching night sweats, weight loss and hemoptysis.
what is Miliary Tuberculosis?
- disseminated TB
- particularly immunocompromised
- Can occur after primary exposure or re-activated secondary TB.
- Spreads via blood stream in macrophages
- Tubercles found in many tissues
- Cancer-like wasting*
what are the complications of miliary TB?
- Miliary spread in lungs due to invasion into the bronchus or lymphatics
- Miliary spread to extra-pulmonary sites
- Due to invasion of pulmonary vein tributaries
- Kidney is the MC extra-pulmonary site
what is the skin test for M tuberculosis?
Mantoux tuberculin test
- CMI response to PPD
how is a diagnosis with M. Tb confirmed? what does this do?
QuantiFERON-TB Test; Test quantitates Interferon γ production by pre-sensitizes cells
how is TB treated?
Isoniazid (Mycolic acid)
Rifampin (RNA Pol)
Pyrazinamide (cell wall)
Ethambutol (membrane)
how do you treat multi-drug resistant TB?
Pyrazinamide
Ethambutol
what vaccine is used to prevent TB?
BCG Vaccine (Bacillus Calmette-Guérin)
