Tuberculosis Flashcards
what stain is used to detect mycobacterium tuberculosis
acid-fast
shape
- rods (bacilli)
- gram-positive cell wall structrue but stain very weakly with gram stain
complex cell wall rich in lipids called
mycolic acids
the acid-fast cell wall has a resistance to
detergents, many antibiotics, and drying conditions
acid fast cell wall functions
protection from lysis after phagocytosis
* blocks fusion of phagosome with lysosome
* masks PAMPS on the bacterial surface
* capacity for intracellular growth within macrophages –> “facultative intracellular pathogen”
reservoir
human
transmission
respiratory droplet nuclei
high or low infectious dose
low
high or low infectious dose
low
populations at greatest risk for TB
- HIV+
- diabetics
- substance abusers
- low body weight/malnourishment
- immunocompromised
pathogenesis (steps 1-3)
- acid fast bacilli are inhaled and spread to alveoli
- phagocytized by alveolar marcophages
- M. tuberculosis capsule and waxy mycoliv acids block pahgosome form fusing with lysosome to avoid destruction within macrophages
pathogenesis (steps 4-6)
- Mycobacteria mulitply in macrophages (intracellular pathogen). Inflammatory response –> other phagocytes are attracted to the site
- macrophages fuse together to form giant multinelceated cells
- A granuloma (aka a tubercle) forms
active secondary TB disease (step 7 of pathogenesis)
suppressed cell mediated immunity –> macrophages in tubercle die –> mycobacteria, enzymes, cytokines released –> forming area of necrosis
* tubercle ruptures, releases live mycobacteria into airways
* causes large defect called tuberculous cavity
* can be transmitted by coughing
active TB signs and symptoms
- chronic cough
- bloody rust-colored sputum
- high fever
- night sweats
- weight loss
- fatigue
miliary TB
when TB gets into ciruclation and spreads systemiclaly to all parts of the body
2 ways TB can develop in HIV-infected person
- pesron with LTBI becomes infected with HIV and then develops TB disease as the immune system is weakened
- person with HIV becomes infected with M. tuberculosis and then rapidly develops TB disease
Skin test for exposure to TB
tuberculin (Mantoux)
what does the tuberculin test do
purified protein derivatives from the Mtb bacterium are inserted intradermaly and read 48-72 laters
lab detection of mycobacteria
acid-fast bacilli (AFB) in sputum
* slow growth, 4-6 weeks
prevention
BCG TB vaccines
BCG TB vaccine
contains a live attenuated BCG strain
* Bacille Calmatte-Guerin
* BCG is a strain of mycobacterium bovis
treatment
- people w/ LTBI can be given treatment to prevent them from developing TB disease
- combination of antibiotic therapy taken everyday for 6 months for uncomplicated TB, otherwise 12-18 months is standard and even longer if MDR-TB strain
