L6 Pathogenesis, Resistance, & Transmission of TB Flashcards
What are the most common symptoms of TB ?
- Hemoptysis
- B symptoms
- fever
- weight loss
- drenching night sweats
What are the M. Tuberculosis complex ? What are the members ?
It causes TB
Members are :
- M. tuberculosis
- M. bovis
- M. africanum
- M. canettii
- M. microti.
What is the structure of Cell wall of M. tuberculosis ?
- Mycolic acid :
- complex hydroxylated ( branched chain fatty acid ) with increases carbon number - Glycolipids :
- responsible of ( the cord formation bacteria ) clump like serpents in liquid medium
Why M. Tuberculosis when stained appears as Gram-positive ?
Mycolic acid causes resistance to de-staining by acid-alcohol after being stained by aniline dyes
What is the shape of M. Tuberculosis after staining with Acid fast stain ?
Pink-staining bacilli
What are the types of media for M. Tuberculosis?
- SOLID ( egg-based medium )
* Lowenstein-Jensen (LJ) medium
* agar-based medium
* Middlebrook 7H10 agar
Require 3-4 weeks to see growth - LIQUID ( BACTEC )
Takes 2 weeks to see the growth
What are the shape of The colonies on Lowenstein-Jensen medium ?
Brown granular colonies
What are the outcomes of exposure to MTB ?
- Immediate clearance of organism
- Rapidly progressive active disease (primary disease)
- Latent infection
- Active disease many years after infection (reactivation disease)
What are the site of primary lung tuberculosis ?
lower part of upper lobe or upper part of lower lobe as it is obligate aerobic and these area have high oxygen tension
What is the mechanism of primary TB ?
- Inhaled bacilli implant in lower part of upper lobe or upper part of lower lobe
- Engulfed by alveolar macrophages in which they multiply causing inflammation and consolidation (Ghon focus)
- Spread of bacilli to regional lymph nodes … Ghon complex or primary complex
What are the cells that you can find in granuloma ?
- Epitheloid cells ( activated microphages )
- Giant cells
- T cells
What is the cause of the induration in mountoux tuberculin test ?
Tissue Infiltration by :
- Lymphocytes
- Mononuclear macrophages
How can miliary TB spread ?
- By blood
- By lymphatics
- By direct spread through swallowing saliva
Where you can find the lesion in primary and secondary TB ?
In primary : upper part of lower lobe or lower part of upper lobe
In secondary : apical sites of the lung
What are the virulent factors of MTB ?
- Mycolic acid glycolipids + trehalose dimycolate»_space;> granuloma formation
- Lipoarabinomannan (LAM)»_space;> produce cytokines that will inhibit oxidative stress
- Sulfatides»_space;> released from the phagosome to inhibit phagosome-lysosome fusion
- Cell wall»_space;> prevent degradation by lysosome if the fusion occur
What are the first and second line treatment of TB ?
- First line :
Sterilizing > rifampicin and pyranizamide
Bactericidal > isonazide and streptomycin and ethambutol - Second line:
* polypeptides
* floroquinlones
* amino-glycoside
* cycloserine
* thionamides
What is most widely used regimen ?
- initial intensive phase of rifampicin, isoniazid, pyrazinamide and ethambutol for 2 months
- rifampicin and isoniazid for 6 months.
What are the types of drug resistance of TB ?
- Mono-resistant TB: Resistant to anyone first-line drug
- Poly-resistant TB: Resistant to at least any 2 first-line drugs (but not both isoniazid and rifampin)
- Multi-drug resistant TB (MDR-TB): Resistant to at least isoniazid + rifampin, possibly additional chemotherapeutic agents.
- Extensively drug resistant TB (XDRTB): Resistant to
* isoniazid + rifampin
* at least one of three injectable second-line drugs (capreomycin, kanamycin, amikacin)
* a fluoroquinolone.
What are the organs that are affected in M. Bovis ?
- Intestine
- Mesenteric lymph node
- Cervical lymph node»_space; scrofula
- Tonsils
What is scrofula ?
It is cervical tuberculosis lymphadenopathy
