Micro: Tuberculosis

Question 1

Mycobacterium tuberculosis is extracellular or intracellular ?

Answer 1

Intracellular.

Question 2

What constituent of M.tuberculosis cell wall (yes there is a cell wall) makes a Gram stain unlikely ?

Answer 2

Mycolic acid !

Question 3

What protective purpose does mycolic acid serve ?

Answer 3

resistant to detergents and common antibiotics

Protects the cell from desiccation (does not dry out)

Question 4

What culture media will M.tuberculosis grow on ?

Answer 4

Lowenstein-Jensen Agar (gold standard for diagnosis but not practical due to long growth period)

Question 5

What diagnostic stain is used to identify M.tuberculosis ?

Answer 5

Acid Fast (Ziehl Nelson stain)

Question 6

What is Cord Factor ?

Answer 6

surface glycolipid which blocks macrophage activation by IFN-γ, induces secretion of TNFα and causes Mycobacterium tuberculosis to form cords in vitro

Allows for anti-microbial resistance to many antibiotics.

Question 7

What causes tissue necrosis in TB ?

Answer 7

Host immune response

Question 8

Describe the signs and symptoms associated with TB

Answer 8

Mild fever , chest pain, cough (productive and often bloody), Fatigue, malaise, weight loss and sweating.

Question 9

Where is M.tuberculosis endemic to ?

Answer 9

Southeast asia
Sub-saharan africa
Eastern Europe

Question 10

Primary tuberculosis

Answer 10

Initial cause of tuberculosis disease

Question 11

Secondary tuberculosis

Answer 11

reactivation of a latent infection

Question 12

Disseminated tuberculosis

Answer 12

involves many (milliary spread)

Question 13

What cells does m.tuberculosis infect intracellularly ?

Answer 13

Alveolar macrophages (much like legionella)

Question 14

Activation and recruitment of alveolar macrophages leads to the formation of …

Answer 14

Tubercle (Granuloma)

Question 15

Caseous lesion

Answer 15

Cheese like interior to a granuloma

Question 16

Ghon complex

Answer 16

Calcified casesou lesion (show up in chest x rays well)

Question 17

Tuberculous cavities

Answer 17

Tubercle that has liquified and formed and air-filled cavity in which bacteria can spread from

Reactivation tuberculosis (secondary)
Aspergillus likes these cavities !

Question 18

Screening

Answer 18

Tuberculin (Mantoux Test)

Question 19

+ Tuberculin. Whats next ?

Answer 19

Chest X-ray for signs of tubercles

Microscopy of sputum (Acid Fast staining of sputum)

Question 20

3rd step is TB diagnosis (not entirely necessary)

Answer 20

Culture on Lowenstein Jensen.

Specific but extremely slow .

Question 21

What are the 4 main drugs used in treatment of tuberculosis ?

Answer 21

Isoniazid
Rifampin
Ethambutol
Pyrazinamide

Question 22

Describe the “Preferred” Regimen for treating TB

Answer 22

Initial: Daily INH, RIF, PZA and EMB for 56 doses (8 weeks)

COntinuation: Daily INH and RIF for 126 doses (18 weeks)

Question 23

Describe the Alternative Regimen for TB treatment

Answer 23

Intial : Daily INH, RIF, PZA and EMB for 14 dosed (2 weeks) the twice weekly for 12 doses (6 weeks)

Continuation: Twice weekly INH and RIF for 36 doses (18 weeks)

Question 24

MDR-TB

Answer 24

Multi-drug resistant TB –> Resistant to Isoniazid and Rifampin ! (Uh Oh)

Question 25

XDR-TB

Answer 25

Extremely drug resistant TB--> Resistant to isoniazid , rifampin and at least one of the other two (ethambutol or pyrazinamide)

Question 26

DOTS

Answer 26

Directly Observed Treatment Short Course

Question 27

Why do we not give out the Bacille Calmette Guerin vaccine in the US ?

Answer 27

We have such a low occurrence of TB and the vaccine would render the Mantoux test ineffective for screening. BCG is a mycobacterium bovis strain.

Question 28

Describe Micobacterium Avium Complex

Answer 28

Mixture of : Mycobacterium Avium and Mycobacterium Intracellulare Weakly G+ Acid Fast Aerobic Rods (Mycolic acid in cell wall)

Question 29

Who typically contracts MAC ?

Answer 29

Immunocomrpromised patients | Chronic Pulmonary disease.

Question 30

Primary MAC

Answer 30

Similar to primary TB

Question 31

Secondary MAC

Answer 31

Dissemination to all organs and blood stream !

Question 32

Who typically get s 2nd MAC ?

Answer 32

AIDS patients with low CD4+ T-Cell counts ( <50 Cells/ml)

Question 33

How do you prevent MAC infection in AIDS patients ?

Answer 33

Constant prophylaxis with Clarithromycin Azithromycin

Question 34

Describe the lab diagnostics of Nocardia

Answer 34

Gram +, Aerobic Weakly Acid fast Branching Filaments (Branched long Rods) Normally found in the soil CUlture: BLood or Chocolate Agar

Question 35

Who is at risk for nocardiosis ?

Answer 35

Immunocompromised | Renal transplants

Question 36

Where does nocardia spread to after forming lung abscesses ?

Answer 36

Brain and kidney (renal patients at increased risk)

Question 37

TOC for Nocardia

Answer 37

IV Trimethoprim-sulfonhexamide (Bactrim) | Linezolid