Infection & Immunology Julie Letchford Flashcards
TB is a major opportunistic infection in ___ patients
HIV and Aids patients
What microorganism is TB caused by? Which organ does it infect preferentially?
Myobacterium tuberculosis,
The lungs
The incidence of Tb is increasing by __% each year
It kills ___ million each year
5%
3 million
Mycobacterium tuberculosis. Fast or slow growing? What kind of bacteria?
Slow growing so takes a while to develop the infection
Bacillus
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?
M tuberculosis
M bovis
M africanum
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
Macrophages burst
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)
Progressive infection
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
FOUR
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?
Rifampicin
Isoniazid
Pyrazinamide
Ethambutol
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?
Liver damage Hypersensitivity 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
Hypersensitivity
Peripheral neuropathy
Liver toxicity
Decreased effects of hormonal contraceptives
Describe anti TB pyrazinamide
Bactericidal prodrug 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?
Joint pain
Liver damage
Hypersensitivity
How does anti TB drug ethambutol work?
Bacteriostatic
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) Joint pain Not used in under 5s
Streptomycin and capreomycin are both amino glycosides. They are ___ line anti TB drugs
Second line
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
What does XDR-TB stand for?
Extreme drug resistance in TB
Strains are resistant to 2 or more first line drugs
AND 3 or more second line drugs!!
Microbials mostly only kill ____ bacteria
Actively growing
Peptidoglycan is present in bacterial cell walls. What’s this made up of?
Alternate NAM and NAG with glycosidic bonds between. These chains are cross linked to other chains via amino acid residues
Peptidoglycan in bacterial cell walls cross linking via an amino acid side chain requires 2 things, what are these?
Transpeptidases (also called penicillin binding proteins)
Loss of a terminal amino acid from the side chain.
What do beta lactams inhibit?
Inhibit cell wall synthesis.
What do the structure of beta lactams all have in common? And what differs?
All have a beta lactam ring
Differ in the Structure of the ring attached to the beta lactam ring and the side chains (R groups)
How do beta lactams work?
1) They bind penicillin binding proteins (PBPs) aka transpeptidases
This prevents cross linking in the bacterial cell wall, loosing rigidity.
2)They mimic d-ala-d-ala residues on peptide side chains
3) stimulate autolysins that break down the cell wall
Why do we have less beta lactams we can use for gram negative bacteria compared to gram positive?
Gram negative have an outer membrane
The beta lactam has to fit through pores in this membrane to access the PBPs
If the beta lactam is too big then won’t fit through the pores
Limited to only small beta lactams
Examples of classes of beta lactams?
Penicillin
Cephalosporin
Monobactams
Carbepenems
Examples of glycopeptides?
Vancomycin
Teicoplanin
How do glycopeptides work?
Bind to terminal d-ala d-ala on peptide side chain
This prevents transglycosylase enzyme from adding a peptidoglycan monomer (NAG—NAM with glycosidic bond) onto the glycan chain.
They can also prevent cross linking
How do polymyxins work?
Disrupt cell membrane
Leakage of cytoplasmic contents
Daptomycin also works at cell membrane
Examples of polymyxins?
Polymyxin A Polymyxin B (colistin)
How do sulphonamides and trimethoprim work?
Metabolic inhibitors of nucleic acid synthesis
How do fluroquinolones work?
Affect DNA replication
What class of antibiotic affect RNA polymerase?
Rifamycins
E.g rifampicin
Remember R and R!!
Nitroimidazoles affect _____
DNA
Ciprofloxacin inhibits DNA replication of bacteria. How?!
Decreases type II and or type IV topoisomerases.
Type II= DNA gyrase
DNA gyrase aids replication by removing supercoils of DNA ahead of replication, so remove DNA gyrase is going to decrease replication!
Top IV: separates DNA after replication.
Fluoroquinolones also act by inhibiting DNA gyrase
Inhibitors of protein synthesis tend to be bacterial______
Bacterial static
Chloramphenicol inhibits protein synthesis in bacteria. How ?
Binds to 50s subunit of bacterial RNA
Decreases peptide bond formation
Macrolides like erythromycin and Clarithromycin inhibit protein synthesis in bacteria. How?
Bind to 50s subunit of RNA
Decrease translocation and release of tRNA
Fucidic acid decreases protein synthesis in bacteria. How?
Binds to EF-G ribosome complex
Decreases translocation of tRNA from A to P site
Where do Cycloserine and bacitracin act?
Act on cell wall synthesis
Where do lincosamides and streptogramins act?
Affect bacterial protein synthesis
Where do sulphonamides and trimethoprim act?
Affect nucleic acid in bacteria
What is the way of remembering the 6 bacteria we are concerned with antibiotic resistance?
E S K A P E Enterococcus faecium Staphylococcus aureus Klebsiella pneumonia Acinetobacter buamanii Pseudomonas aeruginosa Enterobacter
What’s the prob with enterobacter and enterococcus faecium?
We are worried about resistance.
Both of these are opportunistic so if they end up in the wrong place they will cause infection.
Eg enterococcus faecium has been known to cause endocarditis even though it is commonly found in the gut