TB - microbiology, pathophysiology Flashcards
What micro-organism causes TB?
Mycobacterium tuberculosis
What shape is mycobacterium tuberculosis?
Rod-shaped
How does mycobacterium tubercolusis react to oxygen?
Obligate aerobe
meaning it requires oxygen to survive
What is the cell wall of mycobacterium tuberculosis made up of?
Rich in lipids
e.g. mycolic acid
What is the importance of the structure of the cell wall of mycobacterium tuberculosis?
Gram stains cannot pass through cell wall
Resistance against breakdown
What is the virulence factor of mycobacterium tuberculosis?
Its cell wall being rich in lipids e.g. mycolic acid
How long does mycobacterium take to divide?
15-20 hours
What is the importance of mycobacterium tuberculosis taking so long to divide?
Takes a long time to culture
Longer course of antibiotic treatment for TB
How is TB transmitted?
Infected person releases respiratory droplets containing mycobacterium TB when they cough, sneeze
these droplets are in the air
Non-infected person inhales these droplets
What is the relative infectious dose of TB?
Low infectious dose
meaning few mycobacterium TB microbes required to cause TB
What is the relative amount of contact required between people for TB to spread between them?
A lot of contact
significant number of hours per day
Where is mycobacterium TB carried to when it is inhaled?
All the way to the alveoli
What happens to mycobacterium TB in the alveoli?
Macrophages attempt to phagocytose it
engulf it into phagosome
lysosome fuses to form phagolysosome
What happens to mycobacterium TB in the phagolysosomes of macrophages?
Enzymes and ROS released into phagolysosome to destroy mycobacterium TB
but it resists breakdown because of its lipid-rich cell wall
What does mycobacterium TB itself do in the phagolysosomes of macrophages?
Replicates within the phagolysosome
killing the macrophages
Where do the macrophages containing mycobacterium TB travel to?
Draining lymph nodes
What other type of immune cell is involved in defence against mycobacterium TB? Why this type of immune cell?
T cells
because mycobacterium TB is an intracellular pathogen, within macrophages specifically
What do new macrophages migrating to the granuloma do?
Fuse with infected macrophages
to form giant cells, Langhans cells
What do macrophages and T cells fighting against mycobacterium TB form?
Granuloma
What is the name of the granuloma formed in the primary infection?
Ghon’s focus
What is the name of the granuloma formed in the primary infection along with the involvement of the draining lymph nodes?
Primary complex
What happens to the primary infection with TB? Which is more common?
Becomes latent infection - more common
Becomes primary disease
What is the latent infection of TB?
Primary infection is contained but not cleared
meaning immune response prevents mycobacterium TB from replicating and damaging lung tissue, but does not kill it
What is the primary disease of TB?
Primary infection is not contained
mycobacterium TB replicates and damages lung tissue
How severe is the primary disease of TB?
Not severe
patients don’t have many symptoms
What determines whether the primary infection of TB becomes latent infection or primary disease of TB?
Infectious dose
Mycobacterium TB strain
Immune response to mycobacterium TB
What causes the primary infection of TB to become primary disease of TB?
High infectious dose
More virulent mycobacterium TB strain
Defective macrophage and T cell immune response to mycobacterium TB
What happens to the latent infection of TB? Which is more common?
Heals itself - more common
Becomes post-primary disease of TB
What happens when the latent infection of TB heals itself?
Immune response destroys all mycobacterium TB
clearing the infection
What is the post-primary disease of TB?
Mycobacterium TB start replicating
severe damage lung tissue
How severe is the post-primary disease of TB? Why?
Severe
because mycobacterium TB is more aggressive
immune response is more aggressive because fighting against mycobacterium TB for second time
gives symptoms
How else can a person get post-primary disease of TB, aside from the latent infection?
If had latent infection which healed itself
then get re-infected with TB
What are the risk factors for post-primary disease of TB?
HIV infection
Immunosuppressed e.g. corticosteroid drugs, organ transplant
Haematological cancer
Diabetes
How does HIV infection increase risk of post-primary disease of TB?
Low T cell count
poor immune response against mycobacterium TB
How long after the primary infection of TB does post-primary disease of TB occur?
More than 5 years later
