Pharmacology of Antibiotics

Question 1

Name the 5 main classes of antibiotics

Answer 1

Beta-lactams, macrolides, tetracyclines, quinolones, aminoglycosides

Question 2

How are beta-lactams characterised? Give 3 examples of beta-lactams.

Answer 2

. Contain beta-lactam ring

. Penicillin, cephalosporins, glycopeptides

Question 3

How do beta-lactams work? How do some resistant bacteria avoid harm by beta-lactams?

Answer 3

. Target bacterial cell wall synthesis

. Some resistant bacteria secrete beta-lactamases, which destroy beta lactams

Question 4

How do macrolides work? Give an example of two macrolides.

Answer 4

. Cytochrome P450 inhibitors, inhibit bacterial protein synthesis by blocking translocation of bacterial ribosome along mRNA
. Clarithromycin and erythromycin

Question 5

Why are macrolides sometimes preferred over beta-lactams?

Answer 5

Often used as alternative to penicillin (a beta-lactam) for those who are allergic to penicillin

Question 6

How do tetracyclines work?

Answer 6

They inhibit bacterial protein synthesis by binding to bacterial ribosomes and preventing tRNA from binding

Question 7

How do the mechanisms of action of macrolides and tetracyclines differ?

Answer 7

. Both inhibit bacterial translation

. Macrolides block ribosome from moving along mRNA, tetracyclines bind to ribosome to block tRNA from binding

Question 8

Give an example of a quinolone

Answer 8

Ciprofloxacin

Question 9

How do quinolones work in gram-negative bacteria?

Answer 9

Inhibit DNA gyrase/topoisomerase II in gram-negative bacteria (DNA gyrase catalyses supercoiling of DNA in DNA synthesis)

Question 10

How do quinolones work in gram-positive bacteria?

Answer 10

Inhibit topoisomerase IV in gram-positive bacteria (normally topoisomerase IV helps separate the DNA strands in DNA replication)

Question 11

Give an example of an aminoglycoside

Answer 11

Gentamicin

Question 12

How do aminoglycosides work?

Answer 12

Inhibit protein synthesis by causing mRNA to be misread, which interferes with translation

Question 13

Which type of bacteria do aminoglycosides work on?

Answer 13

Gram-negative bacteria

Question 14

What is the main structural difference between gram-positive and gram-negative bacteria?

Answer 14

. Gram positive have thick peptidoglycan cell wall

. Gram negative have thinner cells wall, which is sandwiched between inner and outer cell membranes

Question 15

Which other antibiotic do aminoglycosides work well with?

Answer 15

Penicillin because penicillin can break down the bacterial cell walls, which allows more uptake of aminoglycosides to inhibit protein synthesis

Question 16

Which type of bacteria are more affected by antibiotics?

Answer 16

Gram-positive because although they have a thicker cell wall, they don’t have an outer cell membrane

Question 17

What colours do gram-positive and gram-negative bacteria stain?

Answer 17

. Gram-positive stain dark purple

. Gram-negative stain red/pink