MCBoM- Antibacterials

Question 1

B-lactams

Answer 1

Cell wall synthesis inhibitors
Bind to penicillin binding proteins, inhibiting cross linking of peptidoglycan
Unopposed action of autolysins, more destruction of cell wall than synthesis
Cidal
Gram negative- rupture from osmosis
Gram positive- autolysis via release of lipoteichoic acid
Eg penicillins, cephalosporins

Question 2

Glycopeptides

Answer 2

Cell wall synthesis inhibitors
Bind to portion of pentapeptide required for peptidoglycan formation
Only for gram positive, too big for gram negative
Prevents transpeptidases from bonding, so inhibits peptidoglycan cross linking
Act earlier in cell wall synthesis pathway than B-lactams

Question 3

Aminoglycosides

Answer 3

Protein synthesis inhibitors
Bind to ribosomal 30s subunit
Interfere with mRNA translation/translocation
Cause misreading of mRNA codons, so defective proteins made that disrupt membrane integrity

Question 4

Tetracyclines

Answer 4

Protein synthesis inhibitors
Bind to ribosomal 30s subunit
Block aminoacyl tRNA associating with site on mRNA-ribosome complex, so preventing elongation of peptide
Selective, increased uptake to susceptible bacterial cells
Static, reversible binding

Question 5

Chloramphenicol

Answer 5

Protein synthesis inhibitors
Binds to 50s ribosomal subunit, inhibiting peptidyl transferase and preventing tRNA synthesis
Prevents association with amino acid with peptidyl transferase
Static or cidal depending on bacteria
Can also inhibit human mitochondria protein synthesis which have 50s ribosomal subunit, so bone marrow toxicity, so not used much in clinical practise

Question 6

Sulphonamides

Answer 6

Nucleic acid synthesis inhibitors
Blocks synthesis of tetrahydrofolic acid (precursor of A G and T synthesis)
Competitive inhibitor of folic acid pathway

Question 7

Trimethoprim

Answer 7

Nucleic acid synthesis inhibitors
Inhibits dihydrofolate reductase in folic acid pathway
Greater affinity for bacterial reductase enzyme than human

Question 8

Quinolones

Answer 8

Nucleic acid synthesis inhibitors
Acts at 2 sites:
- DNA gyrase (for coiling DNA), mainly on gram negative rods
- Topoisomerase IV (for DNA relaxation and chromosomal segregation), mainly staph. aureus and other gram positive cocci

Question 9

Daptomycin

Answer 9

Cell membrane disrupter
Semisynthetic lipopeptide
Not very selective, so can cause complicated skin/soft tissue infections in humans