Antibiotic Mechanisms

Question 1

How do aminoglycosides work?

Answer 1

They target protein synthesis by binding to the 30S ribosomal subunit.
They target RNA proofreading.
They cause damage to the cell membrane.

Question 2

Why are some side-effects of aminoglycosides?

Answer 2

They can be slightly toxic to human cells. They can cause hearing loss.

Question 3

Why are we using more aminoglycosides despite their side effects?

Answer 3

Due to resistance to other antibiotics.

Question 4

How does Rifampicin work?

Answer 4

It targets and RpoB subunit of RNA polymerase and so prevents transcription.
It has good activity against bacteria that are within host cells.

Question 5

What are some drawbacks to Rifampicin?

Answer 5

Spontaneous resistance to this drug is frequent.

It also makes secretions turn orange/red, which affects patient compliance to take it for long course.

Question 6

How does Vancomycin work?

Answer 6

It targets the lipid II component of cell wall biosynthesis, as well as wall crosslinking through D-alanine residues.

Question 7

What are some drawbacks to Vancomycin?

Answer 7

It is also quite toxic and needs to be given intravenously, but resistance against other antibiotics has led to increasing use, e.g. against MRSA.

Question 8

How does linezolid work?

Answer 8

It inhibits the initiation of protein synthesis by binding to the 50S rRNA subunit.

Question 9

What sort of bacteria does linezolid work/not work against and why?

Answer 9

It only affects Gram-positive bacteria but does not affect Gram-negative bacteria due to the LPS in the outer membrane.

Question 10

What does daptomycin target?

Answer 10

Bacterial cell membranes.

Question 11

What sort of bacteria does daptomycin work/not work against and why?

Answer 11

It only affects GP bacteria but does not affect GN bacteria due to the LPS in the outer membrane.

Question 12

Why must daptomycin be given limited doses?

Answer 12

It’s toxic.

Question 13

What is the most commonly prescribed antibiotic class?

Answer 13

Beta-lactams.

Question 14

What does beta-lactam refer to?

Answer 14

The beta-lactam ring in their structure (looks like a square with a nitrogen in the corner).

Question 15

How do beta-lactams work?

Answer 15

They interfere with the synthesis of peptidoglycan component of the bacterial cell wall by penicillin-binding proteins, which catalyse a number of steps in the synthesis of peptidoglycan.

Question 16

What are some examples of beta-lactams?

Answer 16

Penicillin and methicillin.

Question 17

Why don’t antibiotics hurt us (most of the time)?

Answer 17

Antibiotics target are selectively toxic. Selective toxicity is facilitated by the large number of differences between mammals and bacterial cells.
In addition, some processes are unique to bacteria such as the production of peptidoglycan and the maintenance of the LPS (lipopolysaccharide) layer of gram-negative bacteria.

Question 18

What are macrolides usually used for?

Answer 18

Gonococci bacteria.

Question 19

How do macrolides work?

Answer 19

It functions by targeting the 50S ribosome subunit, preventing amino-acyl transfer and thus truncation polypeptides, preventing growth.

Question 20

What are quinolones used to treat?

Answer 20

Gonococcus infections as well as some lung and blood infections. They have a broad spectrum of activity.

Question 21

How do quinolones work?

Answer 21

They target DNA gyrase in gram negative bacteria and topoisomerase IV in gram positive. This results in DNA damage and death of the organism.