Microbiology 2 - Antimicrobial agents 1 Flashcards
What is the broad mechanism of action of beta lactams?
Inhibition of cell wall synthesis
What is the broad mechanism of action of glycopeptide antibiotics?
Inhibition of cell wall synthesis
What 3 groups of antibiotics are classified as beta lactams?
Penicillins
Cephalosporins
Carbapenems
Name 2 glycopeptide antibiotics
Vancomycin
Teicoplanin
Describe the mechanism of action of beta lactams
Inhibits transpeptidase, which is an enzyme that forms cross links during the formation of the cell wall.
The resulting cell wall is therefore weak, and so the bacteria lyse because of osmotic pressure.
How does the cell wall of gram pos and gram neg bacteria differ?
- Gram positive cell wall very thick cell wall (made of NAG + NAM components) purple
- Gram negative cell wall thin cell wall, outer membrane conferring resistance to some abx pink
What bacteria is penicillin active against?
Gram pos
What bacteria is amoxicillin active against?
gram +ve, enterococci, gram -ve
Is streptococci gram pos or neg?
Gram pos
Which beta lactam antibiotic is effective against pseudomonas?
Piperacillin (a penicillin)
How can beta lactam resistance be overcome?
Include a beta lactamase inhibitor
Eg. Clavulanic acid + amoxicllin (in co-amoxiclav)
Is pseudomonas gram pos or gram neg?
Gram neg (Pseudo"moan"as - 'moan' = negative)
Is neisseria meningitis gram pos or gram neg?
Gram neg cocci
Neisseria starts with N = negative
Recall an antibiotic that is associated with C. difficile
Ceftriaxone (cephalosporin)
Which beta lactam antibiotics are stable to ESBL organisms?
Carbapenems
Recall a caution of beta lactam antibiotic
Excreted renally so reduce dose if renal impairment
What type of bacteria are glycopeptides effective against?
Gram pos only - they are large molecules so can’t penetrate gram neg cell wall
What are glycopeptides particularly useful for?
MRSA infection
What is a caution of glycopeptide antibiotics?
They are nephrotoxic + to some extent ototoxic
Recall the broad mechanism of action of glycopeptide antibiotics
Prevent peptide cross links in cell wall
Recall the broad mechanism of action of aminoglycosides
Bind to 30s ribosomal subunit, preventing elongation of polypeptide chain
Recall 2 examples of aminoglycoside antibiotics
gentamicin
amikacin
What type of bacteria are aminoglycoside antibiotics effective against?
Gram neg
Recall 2 toxicities of aminoglycosides
Ototoxicity
Nephrotoxicity
What type of bacteria are macrolides effective against?
Gram pos
What are macrolides particularly useful for?
Mild staph or strep infections in patients who are allergic to penicillin
Recall 2 macrolide antibiotics
Azithromycin
Clarithromycin
What type of bacteria are tetracylines effective against?
They are broad spectrum
Useful for intracellular pathogens- chlamydia
E.g doxy
Recall a class of antibiotic you should never give to children or pregnant women
Tetracyclines
Recall one side effect of tetracycline antibiotics
Light-sensitive rash
Recall the broad mechanism of action of macrolides
Bind to the 50s subunit of ribosomes
Recall the broad mechanism of action of tetracyclines
Bind to 30s subunit of ribosomes
What type of bacteria is chloramphenicol effective against?
Many - it is v broad spectrum
Why is chloramphenicol rarely used?
Risk of aplastic anaemia and grey baby syndrome in neonates due to inability to metabolise drug
Recall 2 specific bacteria that macrolides are effective against
Campylobacter sp
Legionella pneumophila
(macrolides = erythromycin/ azithromycin/ clarithromycin)
Useful agent for treating mild Staphylococcal or Streptococcal infections, particularly in penicillin-allergic patients
- Also active against Campylobacter sp and Legionella pneumophillia
o Although most campylobacter is self-limiting so usually don’t give treatment
o Given for atypical pneumonia due to other organisms such as mycoplasma
Recall the broad mechanism of action of chloramphenicol
Binds to 50s subunit of ribosomes - inhibits formation of peptide bonds during translation
Recall the broad mechanism of action of oxazolidinones
Binds to the 23s and 50s subunit of ribosomes to prevent 70s subunit formation
Recall two types of bacteria that oxazolidinones (E.g Linezolid) are particularly active against
MRSA and VRE
MOA: Binds to 23S subunit of 50S, preventing the formation of 70S
Can cause thrombocytopenia
Recall an example of oxazolidinones
Linezolid
Recall one potential side effect of oxazolidinones
Thrombocytopaenia
Recall the broad mechanism of action of fluoroquinolones (E.g ciprofloxacin)
Act on alpha subunit of DNA gyrase
Recall 4 uses of fluoroquinolones
UTI
Pneumonia
Atypical pneumonia
Bacterial gastroenteritis
Gram -ve organisms
E.g ciprofloxacin
MOA: Act on alpha subunit of DNA gyrase
Recall 3 examples of fluoroquinolone antibiotics
Levofloxacin
Moxifloxacin
Ciprofloxacin
Give an example of a nitromidazole antibiotic
Metronidazole
Recall types of organisms that metronidazole is effective against
Anaerobes
Protozoa
When should nitrofurantoin be taken?
Right after visiting the toilet as it sits in bladder and is absorbed through the bladder, not systemically
Recall the broad mechanism of action of rifampicin
Binds to DNA-dependent RNA polymerase to inhibit RNA synthesis
Recall the main use of rifampicin
TB treatment
Recall one side effect of rifampicin
Turns secretions orange
Recall one condition of rifampicin prescription
Should never be prescribed alone as resistance develops very quickly (very important)
CYP450 inducer- so have to be careful about other drugs you are giving. E.g for COCP, you are advised not to take it and to take either IUS,IUD,Depoprovera instead, but if you are using COCP, double the dose.
Colistin is very toxic. Why is it coming back into use?
It is active agianst certain multi-drug resistant bacteria
What is daptomycin (Cell membrane toxin) licensed for the treatment of?
MRSA
VRE
Gram+ organisms
Linezolid (inhibits protein synthesis- binds 23s on 50s, preventing 70s) has same coverage
Recall the 2 classes of antibiotic that inhibit folate synthesis
Sulphonamides (e.g sulfomethoxazole)
Diaminopyrimidines (e.g trimethoprim)
The combination of the two (co-trimoxazole/sulfomethoxazole-trimethoprim) is a valuable antimicrobial in certain situations (e.g. treating Pneumocystis jiroveci pneumonia)
Give an example of a sulphonamide
Sulfamethoxazole
What is the main use of trimethoprim
Uncomplicated/community acquired UTI
What are the 4 main mechanisms of resistance
- Inactivation (eg beta latcamases)
- Altered target (so antibiotic no longer binds - important in MRSA where bacteria change the penicillin-binding protein, and in protein-synthesis inhibitors where the binding of the ribosome subunit is prevented)
- Reduced accumulation
(most important in gram negs - either due to efflux or to reduced uptake) - Bypass
(particularly important for folate inhibitors - bacteria can change the enzyme they use)
Which antibiotic is best for treating pseudomonas jirovecii?
Co-trimoxazole
What is the broad mechanism of action of nirtromidazoles?
Inhibit DNA synthesis (Under anaerobic conditions, an active intermediate is produced which causes DNA strand breakage)
E.g Metronidazole, Tinidazole
Active against anaerobic bacteria and protozoa (e.g. Giardia)
Which bacteria typically forms “gram pos cocci in clusters”?
Staphylococcus
Which bacteria typically forms “gram pos cocci in chains”?
Streptococcus
Strep sounds like ‘stripe’ = chain
What gram stain status are enterococci?
Positive
“Enter-o-coccus” = like letting someone in, positive thing to do
Is haemophilus gram pos or neg?
Gram neg
Ha”emo”philus - emo = negative
Is listeria gram pos or neg?
Positive
Lister = good man = positive
