MCB Lecture 51 Antimicrobial Agents

Question 0

Why do we make semi-synthetic drugs?

Answer 0

Change the spectrum, kinetics and toxicity

Question 1

Differentiate between antibiotics, chemo therapeutic agents and semi-synthetic drugs

Answer 1

Antibiotic: naturally occuring
Chemotheraputic agent: man made
Semi-synthetic: naturally occuring, but has been altered

Question 2

What are the ways that we can classify antimicrobial drugs? (3)

Answer 2

Source
Mode of action
Pharmological class

Question 3

What are the two effects that antimicrobial agents can have on bacterial growth?

Answer 3

Bactericidal

Bacteria static

Question 4

What are tetracyclines?

Answer 4

These are antimicrobial agents that have four rings in the structure

Question 5

What is the structure of Beta-lactams?

Answer 5

Square, pentagon, N, S, O

Question 6

What are some of the types of antibiotics that are examples of the beta-lactam class?

Answer 6

Penicillins

Cephalosporins

Question 7

How were beta lactam semi-synthetic drugs developed?

Answer 7

Start from the naturally occuring one, then modify it to change the toxicity, spectrum etc.

Question 8

Describe the development of the different penicillins

Answer 8

Penicillin G, very low toxicity, no good against GNR, must be injected.
Penicillin V, can now be taken orally

Ampicillin, now effective against GNR
Methicillin, effective against golden staff, but toxic
Flucloxacillin, less toxic than methicillin
Carbenicillin, effective against Pseudomonas

Question 9

Which type of penicillin is the first to be effective against pseudomonas?

Answer 9

Carbenicillin

Question 10

What is the difference between Methicillin and Flucloxacillin?

Answer 10

Flucloxacillin is less toxic than methicillin

Question 11

Why was ampicillin important?

Answer 11

It was now effective against GNR

Question 12

Describe the differences between Penicillin G and Penicillin V

Answer 12

Penicillin V can now be taken orally

Question 13

What is meant by selective toxicity

Answer 13

This means that it only targets elements of the bacteria

Question 14

Who discovered Penicillin?

Answer 14

Fleming and Florey

Question 15

What are some of the different features that antimicrobial agents target?

Answer 15

Cell wall
Protein synthesis (ribosomes)
Cell membrane
Nucleic acid
Folic acid

Question 16

Describe broadly how antimicrobial agents target the cell wall

Answer 16

Block the building of the peptidoglycan, so the cell has an influx of water, so the cell lyses

Question 17

Describe the synthesis of the prokaryotic cell wall

Answer 17

1. The subunit precursors are made inside the cell

2. Moved to the outside of the cell and linked together

Question 18

Which enzymes catalyse the connections between the peptidoglycan subunits?

Answer 18

Transpeptidases

Question 19

What are two classes of drug that target the cell wall

Answer 19

Beta lactams (Penicillin) and Glycopeptides (vancomycin)

Question 20

Describe the action of vancomycin

Answer 20

Binds to the D-alas on the peptide chains of the peptidoglycan subunits. Now, the blocks can’t be connected

Question 21

Describe how bacteria may become resistant to vancomycin

Answer 21

They replace one of the D-ala with a sugar so that vancomycin can not bind

Enerococci do this

Question 22

What are penicillin binding proteins?

Answer 22

These are normal proteins found in bacteria that are required for connection of peptidoglycan synthesis

They are also known as transpeptidases

Question 23

How does penicillin work?

Answer 23

It binds to transpeptidases, rendering it inactive

Question 24

Describe how bacteria may become resistant to penicillin (2)

Answer 24

1. Altered penicillin binding proteins

2. Beta-lactamase breaks down penicillin

Question 25

Describe broadly how antimicrobial agents target protein synthesis

Which agents do this?

Answer 25

Aminoglycosides

They bind to the 30S of ribosomes and mess up the reading frame so that abnormal proteins are made

Question 26

Describe the action of amino glycosides

Answer 26

1. Bind to 30S subunit
2. Mess up the reading frame
3. Misense or nonsense mutation: abnormal protein made
4. Abnormal protein is associated into important structures in the bacteria

Question 27

Describe how bacteria may become resistant to Aminoglycosides

Answer 27

1. Change the 30S so that the Aminoglycoside can not bind

2. Bacteria modify the Aminoglycoside so that it can not get in

Question 28

What is important about metronidazole?

Answer 28

It is selectively toxic to bacteria, because it requires reductase enzymes (only found in bacteria) to be activated

Question 29

Describe the two genetic bases for antibiotic resistance

Answer 29

Innate: the resistance is part of the naturally occuring bacteria
Eg. G- bacterial cell wall is resistant due to impermeability

Acquired: mutation, or plasmid

Question 30

Describe the problem that multi resistance plasmids present

Answer 30

One we apply one antimicrobial agent to these bacteria, every single other resistance on the plasmid is selected for, so we get multi resistant bacteria

Question 31

Give an exams of a glycopeptide.

What does it do?

Answer 31

Vncomycin

It blocks cell wall formation

Question 32

What do tetracyclines do?

Answer 32

They interfere with the recognition phase of protein synthesis

Question 33

What does chloramphenicol do?

Answer 33

It interferes with peptidyl transfer in translation

Question 34

What are some examples of aminoglycosides?

Answer 34

Gentamicin
Tobramycin
Amikacin