micro 4 (TB)

Question 1

General characteristics of Mycobacteria (5)

Answer 1

1- aerobic, non-spore-forming, immotile
2- gram-positive
3- high in mycolic acid (hydrophobic)
4- slow growth rate
5- grows on Lowenstein-jenson media

Question 2

what are the main virulence factors of TB? (2)

Answer 2

1- Prevention of phagosome fusion with lysosomes
2- Catabolism of oxidants thus preventing the formation of superoxide anions

Question 3

what is the tissue morphology of TB?

Answer 3

visible tissue necrosis with granulomatous caseating necrosis

Question 4

in primary TB, what is ‘Ghon complex’?

Answer 4

Ghon focus (visible calcification of the lung parenchyma) + hilar LN

Question 5

what is the ‘tuberculin skin test’ (Mantoux test) and what does it indicate?

Answer 5

its the intradermal injection of PPDs (purified protein derivatives) extracted from M. tuberculosis. if there is a skin reaction, then this indicates primary tuberculosis

Question 6

what are the features of progressive TB?

Answer 6

• middle and lower lobes are affected
• hilar lymphadenopathy > obstruction
• segmental TB: due to the progression of Ghon focus
• hemorrhage
• bacteremia and ‘miliary TB’

Question 7

in what case does tuberculin test render false positive?

Answer 7

if the patient is vaccinated with BCG

Question 8

what do macrophages secrete in response to TB? (2)

Answer 8

IL-12: secrete IFNγ. → enhances the
fusion of phagosomes with lysosomes.
* TNFα: act on the macrophages themselves to stimulate the formation of the reactive nitrogen intermediates

Question 9

what does TB spread through the pulmonary vein cause?

Answer 9

systemic military TB or single organ involvement

Question 10

what does TB spread through the pulmonary arteries cause?

Answer 10

localized pulmonary miliary TB

Question 11

what route of spread can cause diffuse pulmonary miliary TB?

Answer 11

through the lymphatic system

Question 12

what is the most accurate immunodiagnosis technique for TB? give one example

Answer 12

IFNγ-release assays (IGRAs): such as QuantiFERON-TB Gold

Question 13

what are the primary stains used to detect mycobacteria under the microscope? (2)

Answer 13

A. Carbol fuchsin: ‘Ziehl-Neelsen’ technique or the cold ‘Kinyoun’ technique before examination under the brightfield microscope.
B. auramine-rhodamine: under
fluorescent microscope, → more sensitivity

Question 14

what is MDR-TB resistant to?

Answer 14

Resistance to isoniazid and rifampicin

Question 15

what are three examples of rapidly growing mycobacteria?

Answer 15

M. fortuitum, M. chelonae. & M. abscessus

Question 16

what is the C/P of rapidly growing mycobacteria?

Answer 16

multilobar, cavitation, and associated with bronchiectasis