Mycobacterium TB

Question 1

What type of bacteria is mycobacterium tb?

Answer 1

Obligate aerobe. It is an acid fast bacilli (somewhere between Gram +tve and -tve)

Question 2

What are the 3 different types of TB?

Answer 2

Primary TB Post primary TB Milliary TB

Question 3

What is primary TB?

Answer 3

Usually symptomless- possible cough or wheeze Small transcient pleural effusion may occur 25-30% of people have latent TB in their granalomas (symptomless and dormant)

Question 4

What is post-primary TB?

Answer 4

Onset of symptoms over weeks/months Symptoms include weight loss, fever, blood-stained spit, plueral effusion

Question 5

What is miliary TB?

Answer 5

Wide dissemination of TB from the lymph nodes via hematogenous dissemination (the blood) Spreads throughout entire body, fatal without treatment >1.5% of cases are miliary

Question 6

Where does TB first enter in its pathogenesis?

Answer 6

TB enters via the airways into the alveolar sacs, in which it will be engulfed by alveolar macrophages

Question 7

What happens after TB is engulfed by macrophages?

Answer 7

It will reside in macrophage and replicate intracellularly by inhibiting the fusion of phagosomes with lysosomes

Question 8

What will happen to the infected macrophages in primary (latent) TB?

Answer 8

Pro-inflammatory responses (recruitment of additional monocytes and lymphocytes) will causes wbcs to assemble around the macrophage, forming a granuloma

Question 9

What is a granuloma wrt TB?

Answer 9

Granuloma is the hallmark of TB, and can arrest TB growth (causing it to be latent TB)

Question 10

What can happen to infected macrophages in post-primary/miliary TB?

Answer 10

Infected cells will migrate to local draining lympth nodes, allowing TB to infect other regions of the lung (or body in miliary TB)

Question 11

What can happen to the granulomas over time?

Answer 11

If the immune system weakens, necrosis of macrophages in granuloma may allow TB to grow and spread

Question 12

What is a calcified granuloma?

Answer 12

Over time calcium deposits can build up in granulomas, causing them to harden; this may result in the eradication of TB from the body

Question 13

What are 3 important virulence factors for TB?

Answer 13

ESX-1 secretion system
LAM glycolipid
Mycolic acids

Question 14

How does ESX-1 secretion system act as a virulence factor?

Answer 14

Crucial for secretion of proteins like ESAT-6, which is known to (sometimes in conjunction with CFP-10) modulate host immune response to help survival and proliferation of TB

Question 15

How do LAM glycolipids act as a virulence factor?

Answer 15

It is found in the cell wall of M. tb, and inhibits the fusion of phagosomes with lysosomes in macrophages, preventing destruction of TB

Question 16

How do mycolic acids act as a virulence factor?

Answer 16

Major component of TB cell wall. They provide a barrier that grants protection to bacteria from host immunomodulatory molecules and antibiotics.
Cord factor consists of two mycolic acid molecules, and has been shown to induce formation of granulomas, which helps TB persist in host

Question 17

What are two tests for TB?

Answer 17

Mantoux tuberculin skin test
Interferon gamma release assay