Antibiotic Classes

Question 1

Name the different mechanisms of action of antibiotics?

Answer 1

1. Inhibit cell wall synthesis
2. Inhibit protein synthesis
3. Interfere with DNA synthesis
4. Disrupts cell membrane

Question 2

Name the 3 groups of cell wall synthesis inhibitors?

Answer 2

1. Beta-lactams (penicillins, cephalosporins, carbapanems)
2. Glycopeptides (e.g. vancomycin)
3. Isonazid

Question 3

Name the 3 types of Beta-lactams?

Answer 3

Penicillins, Cephalosporins, Carbapanems

Question 4

Are B-lactams bactericidal or bacteriostatic?

Answer 4

Bactericidal

Question 5

What is the mode of action of B-lactam antibiotics?

Answer 5

B-lactams act against bacteria by inhibiting the synthesis of the peptidoglycan layer in the bacterial cell walls.

The B-lactam ring structure is capable of binding to the enzymes with cross-link the peptidoglycan layers (transpeptidase/penicillin-binding proteins).

The result: damage to cell. gram-positive bacteria have high osmotic pressure, without a rigid cell wall, the cells burst when subjected to the low osmotic pressure of their surrounding environment.

Question 6

Peptidoglycan is a polymer of what?

Answer 6

NAM (N-acetyl muramic acid)

NAG (N-acetyl glucosamine)

Question 7

Summarise the process of peptidoglycan synthesis

Answer 7

1. NAG is added to NAM to form a precursor of peptidoglycan
2. Precursor transported across the cell membrane
3. Precursors undergo cross-linking to create cell wall (x2 major enzymes involved: transpeptidases (aka penicillin-binding proteins)

Question 8

What is the basic mechanism of B-lactam resistance?

Answer 8

alteration of the penicillin binding proteins
and
beta-lactamase

Question 9

Action of beta-lactamase enzymes? how is this overcome clinically?

Answer 9

Bacteria produce enzymes called beta-lactamases in an attempt to overcome the action of the antibiotics. The b-lactamases break open the beta lactam ring, rendering inactive.

overcome clinically: b-lactamase inhibitors

Question 10

Give an example of beta-lactamase inhibitor? How does it work?

Answer 10

Clavulanic Acid
has a similar structure to antibiotic, beta-lactam ring
blocks the active site of the beta lactamases to prevent them from destroying the antibiotic

Question 11

Give an example of an antibiotic + inhibitor combination?

Answer 11

Amoxicillin + Clavulanic Acid

= Co-amoxiclav

Question 12

What is the mechanism of the glycopeptide antibiotics?

Answer 12

glycopeptides also inhibit cell wall synthesis.
BUT bind directly to the side-chains, rather than the transpeptidases/PBPs.
result = PBPs can’t access the side chains

Question 13

When might a glycopeptide be preferential over a beta-lactam antibiotic?

Answer 13

In cases of MRSA - resistance.
(MRSA - flucloxacillin resistant form of s.aureus)

against MRSA, glycopeptides would still work, for example: Vancomycin

Question 14

Example of a Carbapenem?

Answer 14

Meropenem

Question 15

What time of bacteria is vancomycin best to use against?

Answer 15

gram(+) - cell wall, peptidoglycan

virtually ineffective against gram(-)

Question 16

What are the 3 groups of protein synthesis inhibitors?

Answer 16

1. Macrolides
2. Aminoglycosides
3. Tetracyclines

Question 17

What is the mode of action of the protein synthesis inhibitors?

Answer 17

bind to the ribosome and block translation (no amino acid chain forms)

target either 30s or 50s sub-unit

Question 18

Which antibiotic group targets the 50s sub-unit of the ribosome?

Answer 18

Macrolides

Question 19

Which antibiotic group targets the 30s sub-unit of the ribosome?

Answer 19

Aminoglycosides

Tetracyclines

Question 20

Name the 3 antibiotic groups that interfere with DNA synthesis/replication?

Answer 20

1. Sulphonamides
2. Diaminopyrimidines
3. Quinolones

Question 21

What is the mechanism of action of the sulphonamides?

Answer 21

they block nucleotide synthesis!
bacteria can’t absorb folate like human cells, have to synthesise it - they are folate synthesis inhibitors

block enzyme at earlier stage of infection

Question 22

What is the mechanism of action of the Diaminopyramidines?

Answer 22

they block nucleotide synthesis!
bacteria can’t absorb folate like human cells, have to synthesise it - they are folate synthesis inhibitors

blocks enzyme at later stage of infection

Question 23

Example of a Diaminopyramidine antibiotic?

Answer 23

Trimethoprim

Question 24

What is the mechanism of action of the Quinolones?

Answer 24

DNA gyrase inhibitor
stops the DNA unwinding before replication

rapidly fatal!

Question 25

Example of a Quinolone?

Answer 25

Ciprofloxacin

associated with C.diff

Question 26

Why might you give a sulphonamide and diaminopyramidine together?

Answer 26

synergistic activity
reduce resistance
and more powerful effect!

Question 27

Whats different between fungus and bacteria?

Answer 27

fungus = eukaryotic

Question 28

Mechanism of action of anti-fungal drugs?

Answer 28

interfere with the cell membrane
block ergosterol production

or block the cell wall

Question 29

Give 3 examples of Bactericidal antibiotics?

Answer 29

Penicillins, gentamicin (aminoglycoside), ciprofloxacin

Question 30

Give 2 examples of Bacteriostatic antibiotics?

Answer 30

Tetracyclines, sulphonamides

Question 31

In what situation, are bactericidal antibiotics preferred?

Answer 31

in immunocompromised patients, or when infection is in difficult to reach sites (endocarditis, meningitis)

Question 32

What are the four criteria for switching from IV to oral antibiotics?

Answer 32

COMS

C: Clinical improvement observed
O: Oral route is not compromised
M: Markers showing a trend towards normalising
S: Specific indication of deep infection (ABSENCE OF!)