Flashcards in Infection & Immunology Julie Letchford Deck (141)
What microorganism is TB caused by? Which organ does it infect preferentially?
TB is a major opportunistic infection in ___ patients
HIV and Aids patients
The incidence of Tb is increasing by __% each year
It kills ___ million each year
Mycobacterium tuberculosis. Fast or slow growing? What kind of bacteria?
Slow growing so takes a while to develop the infection
The mycobacterium tuberculosis cell wall is rich in lipids. What does this result in?
Very hydrophobic therefore resistant to drying and to weak disinfectants
What's the mycobacterium tuberculosis complex?
And M microti
A group of genetically related mycobacterium species that can cause tuberculosis
What is stage 1 of the progression of primary TB?
Bacilli is inhaled in droplets (respiratory droplets from someone)
Then phagocytosed by macrophages non specifically
These do not destroy the bacilli!
What is stage 2 of the progression of primary TB?
Mycobacterium TB multiplies inside macrophages for 7-21 days
Other macrophages may phagocytose the released TB
What happens at stage 3 of the progression of primary TB?
Cell mediated response initiated
T cells and B cells and collagen fibres (show up well on X-ray) all accumulate
Tubercules form with a caseous necrosis centre of dead matter
Once the Tubercules are formed at stage 3 of TB progression, what three ways may the infection now go?
Infection cleared away by immune system
Infection lies dormant and deactivates at later date (latent)
What happens at stage 4 of TB progression?
Bacteria multiply inside macrophages and there's uncontrolled lysis (bursting)
Enzymes get released and destroy local tissue forming lesions
What can we see on an X-ray of TB?
White lesions formed from enzymes from broken down macrophages replace alveoli with scar tissue.
Collagen fibres show up well
What is the tuberculin skin test?
Tuberculin is injected into forearm
A positive result: skin lesion (red region) over 10mm diameter forms after 48-72 hours.
Tuberculin is a protein derived from the TB bacteria
To treat TB first line we tend to treat with ____ antibiotic drugs in one go
Stops all the bacteria becoming resistant as there's so many, if we used just one could easily become resistant
What are the four first line anti TB drugs?
Describe the effects of rifampicin on TB
Bactericidal- kills off dividing cells, inhibits RNA polymerase
Taken orally, fully absorbed
Decreased effects by food.
What are the side effects of rifampicin?
Decreased activity of other drugs
Red coloured body fluids (red wee)
Describe the characteristics of anti TB drug Isoniazid
Bactericidal or bacteriostatic
It's a prodrug
Decreases synthesis of mycolic acid
Usually oral, but can be IV or IM
What are the side effects of anti TB isoniazid
Decreased effects of hormonal contraceptives
Describe anti TB pyrazinamide
Decreases synthesis of mycolic acid
Damages the bacterial membrane
This is the only drug that can truly kill dormant bacteria
Well absorbed orally
What are the side effects of anti TB drug pyrazinamide?
How does anti TB drug ethambutol work?
Increases permeability of bacterial cell walls
Orally well absorbed
50% excreted unchanged in urine
What are the side effects of anti TB drub Ethambutol?
Optic neuritis (blurring, but reversible)
Not used in under 5s
Streptomycin and capreomycin are both amino glycosides. They are ___ line anti TB drugs
Cycloserine, Ciprofloxacin and azithromycin are examples of?
Second line anti TB drugs
What would be a treatment regimen for active TB (ripe)?
Rifampicin and isoniazid for 6-9 months
Pyrazinamide for 2 months plus ethambutol
What would be a treatment regimen for latent TB?
Treat with immuno suppressants
Rifampicin for 6 months
Or rifampicin and isoniazid for 3 months
Why do we need a long duration of therapy for treating TB?
Bacteria in macrophages and Tubercules: hard for drug to penetrate
Rupturing of lesions: renewed infection
Drugs are only bactericidal against actively growing organisms, not dormant ones
What does MDR-TB mean?
Moderate drug resistance in TB
Strains are resistant to 2 or more first line drugs