TB - microbiology, pathophysiology

Question 1

What micro-organism causes TB?

Answer 1

Mycobacterium tuberculosis

Question 2

What shape is mycobacterium tuberculosis?

Answer 2

Rod-shaped

Question 3

How does mycobacterium tubercolusis react to oxygen?

Answer 3

Obligate aerobe

meaning it requires oxygen to survive

Question 4

What is the cell wall of mycobacterium tuberculosis made up of?

Answer 4

Rich in lipids

e.g. mycolic acid

Question 5

What is the importance of the structure of the cell wall of mycobacterium tuberculosis?

Answer 5

Gram stains cannot pass through cell wall

Resistance against breakdown

Question 6

What is the virulence factor of mycobacterium tuberculosis?

Answer 6

Its cell wall being rich in lipids e.g. mycolic acid

Question 7

How long does mycobacterium take to divide?

Answer 7

15-20 hours

Question 8

What is the importance of mycobacterium tuberculosis taking so long to divide?

Answer 8

Takes a long time to culture

Longer course of antibiotic treatment for TB

Question 9

How is TB transmitted?

Answer 9

Infected person releases respiratory droplets containing mycobacterium TB when they cough, sneeze
these droplets are in the air
Non-infected person inhales these droplets

Question 10

What is the relative infectious dose of TB?

Answer 10

Low infectious dose

meaning few mycobacterium TB microbes required to cause TB

Question 11

What is the relative amount of contact required between people for TB to spread between them?

Answer 11

A lot of contact

significant number of hours per day

Question 12

Where is mycobacterium TB carried to when it is inhaled?

Answer 12

All the way to the alveoli

Question 13

What happens to mycobacterium TB in the alveoli?

Answer 13

Macrophages attempt to phagocytose it
engulf it into phagosome
lysosome fuses to form phagolysosome

Question 14

What happens to mycobacterium TB in the phagolysosomes of macrophages?

Answer 14

Enzymes and ROS released into phagolysosome to destroy mycobacterium TB
but it resists breakdown because of its lipid-rich cell wall

Question 15

What does mycobacterium TB itself do in the phagolysosomes of macrophages?

Answer 15

Replicates within the phagolysosome

killing the macrophages

Question 16

Where do the macrophages containing mycobacterium TB travel to?

Answer 16

Draining lymph nodes

Question 17

What other type of immune cell is involved in defence against mycobacterium TB? Why this type of immune cell?

Answer 17

T cells

because mycobacterium TB is an intracellular pathogen, within macrophages specifically

Question 18

What do new macrophages migrating to the granuloma do?

Answer 18

Fuse with infected macrophages

to form giant cells, Langhans cells

Question 19

What do macrophages and T cells fighting against mycobacterium TB form?

Answer 19

Granuloma

Question 20

What is the name of the granuloma formed in the primary infection?

Answer 20

Ghon’s focus

Question 21

What is the name of the granuloma formed in the primary infection along with the involvement of the draining lymph nodes?

Answer 21

Primary complex

Question 22

What happens to the primary infection with TB? Which is more common?

Answer 22

Becomes latent infection - more common

Becomes primary disease

Question 23

What is the latent infection of TB?

Answer 23

Primary infection is contained but not cleared

meaning immune response prevents mycobacterium TB from replicating and damaging lung tissue, but does not kill it

Question 24

What is the primary disease of TB?

Answer 24

Primary infection is not contained

mycobacterium TB replicates and damages lung tissue

Question 25

How severe is the primary disease of TB?

Answer 25

Not severe | patients don't have many symptoms

Question 26

What determines whether the primary infection of TB becomes latent infection or primary disease of TB?

Answer 26

Infectious dose Mycobacterium TB strain Immune response to mycobacterium TB

Question 27

What causes the primary infection of TB to become primary disease of TB?

Answer 27

High infectious dose More virulent mycobacterium TB strain Defective macrophage and T cell immune response to mycobacterium TB

Question 28

What happens to the latent infection of TB? Which is more common?

Answer 28

Heals itself - more common Becomes post-primary disease of TB

Question 29

What happens when the latent infection of TB heals itself?

Answer 29

Immune response destroys all mycobacterium TB | clearing the infection

Question 30

What is the post-primary disease of TB?

Answer 30

Mycobacterium TB start replicating | severe damage lung tissue

Question 31

How severe is the post-primary disease of TB? Why?

Answer 31

Severe because mycobacterium TB is more aggressive immune response is more aggressive because fighting against mycobacterium TB for second time gives symptoms

Question 32

How else can a person get post-primary disease of TB, aside from the latent infection?

Answer 32

If had latent infection which healed itself | then get re-infected with TB

Question 33

What are the risk factors for post-primary disease of TB?

Answer 33

HIV infection Immunosuppressed e.g. corticosteroid drugs, organ transplant Haematological cancer Diabetes

Question 34

How does HIV infection increase risk of post-primary disease of TB?

Answer 34

Low T cell count | poor immune response against mycobacterium TB

Question 35

How long after the primary infection of TB does post-primary disease of TB occur?

Answer 35

More than 5 years later