Antibiotics

Question 1

Describe penicillins - type of antibiotic and mode of action

Answer 1

β-lactam antibiotics

Mode of action - target cell wall synthesis by irreversibly binding to a transpeptidase that is involved in cross-linkage of peptidoglycan in bacterial cell wall

Only effective against dividing organisms

Question 2

What are β-lactamases

Answer 2

Produced by resistant bacteria

Clavulanic acid can be added to antibiotics to counteract this

Question 3

What are cephalosporins

Answer 3

β-lactam antibiotics

Act in similar way to penicillins; therefore allergy to penicillin applies to cephalosporins as well

Question 4

Describe glycopeptides - what are they and what is their mode of action

Answer 4

Inhibit bacterial cell wall synthesis by inhibiting growth of peptidoglycan chain
Used to manage severe infections
Mostly bactericidal

Question 5

Describe tetracyclines

Answer 5

Inhibit protein synthesis by binding to the 30s subunit of the ribosome and preventing tRNA from binding at the acceptor site
This means they are bacteriostatic = bacteria unable to grow so immune system can then remove them
Decreased use due to resistance
Can be used instead of penicillin in those with allergies

Question 6

Describe macrolides

Answer 6

Prevent translocation of the 50s subunit of ribosome along the mRNA = prevent protein synthesis = bacteriostatic
Often used as alternative to penicillin
Powerful inhibitors of cytochrome P450 (liver drug metabolism enzyme) ; can cause interacting drugs(such as simvastatin) to increase to toxic levels

Question 7

Describe aminoglycosides

Answer 7

Bactericidal
Bind irrreversibly to the 30s subunit of bacterial ribosomes , leading to misreading of mRNA and protein synthesis interference
Used for gram-negative bacteria
Given in conjunction of penicillins ; breakdown of cell wall via penicillin increases uptake of aminoglycosides

Question 8

Describe quinolones

Answer 8

Bactericidal
Inhibitors of bacterial DNA gyrases

In gram negative bacteria - supercoiling of bacterial DNA is inhibited ; essential for DNA replication

In gram positive bacteria - separation of DNA strands for replication is inhibited

Question 9

Describe the mode of action of trimethoprim

Answer 9

Commonly used for UTIs

Folate antagonist and bacterial dihydrofolate reductase inhibitors (needed to convert folate to tetrahydrofolate which is used to make DNA)

Bacteriostatic

Interacts with alcohols badly

Question 10

Describe sulphonamides

Answer 10

Analogues of p-aminobenzoic acid (PABA)
Competitive inhibitors of dihydropteroate synthase which make folate from PABA

Availability of DNA/RNA precursors is reduced

Question 11

Describe the action of metronidazole

Answer 11

Pro-drug that’s is activated by anaerobic bacteria/Protozoa to become cytotoxic