MCB Lecture 51 Antimicrobial Agents Flashcards Preview

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Flashcards in MCB Lecture 51 Antimicrobial Agents Deck (35)
0

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

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

1

Why do we make semi-synthetic drugs?

Change the spectrum, kinetics and toxicity

2

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

Source
Mode of action
Pharmological class

3

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

Bactericidal
Bacteria static

4

What are tetracyclines?

These are antimicrobial agents that have four rings in the structure

5

What is the structure of Beta-lactams?

Square, pentagon, N, S, O

6

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

Penicillins
Cephalosporins

7

How were beta lactam semi-synthetic drugs developed?

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

8

Describe the development of the different penicillins

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

9

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

Carbenicillin

10

What is the difference between Methicillin and Flucloxacillin?

Flucloxacillin is less toxic than methicillin

11

Why was ampicillin important?

It was now effective against GNR

12

Describe the differences between Penicillin G and Penicillin V

Penicillin V can now be taken orally

13

What is meant by selective toxicity

This means that it only targets elements of the bacteria

14

Who discovered Penicillin?

Fleming and Florey

15

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

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

16

Describe broadly how antimicrobial agents target the cell wall

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

17

Describe the synthesis of the prokaryotic cell wall

1. The subunit precursors are made inside the cell
2. Moved to the outside of the cell and linked together

18

Which enzymes catalyse the connections between the peptidoglycan subunits?

Transpeptidases

19

What are two classes of drug that target the cell wall

Beta lactams (Penicillin) and Glycopeptides (vancomycin)

20

Describe the action of vancomycin

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

21

Describe how bacteria may become resistant to vancomycin

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

Enerococci do this

22

What are penicillin binding proteins?

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

They are also known as transpeptidases

23

How does penicillin work?

It binds to transpeptidases, rendering it inactive

24

Describe how bacteria may become resistant to penicillin (2)

1. Altered penicillin binding proteins
2. Beta-lactamase breaks down penicillin

25

Describe broadly how antimicrobial agents target protein synthesis

Which agents do this?

Aminoglycosides

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

26

Describe the action of amino glycosides

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

27

Describe how bacteria may become resistant to Aminoglycosides

1. Change the 30S so that the Aminoglycoside can not bind
2. Bacteria modify the Aminoglycoside so that it can not get in

28

What is important about metronidazole?

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

29

Describe the two genetic bases for antibiotic resistance

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

Acquired: mutation, or plasmid

30

Describe the problem that multi resistance plasmids present

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

31

Give an exams of a glycopeptide.

What does it do?

Vncomycin

It blocks cell wall formation

32

What do tetracyclines do?

They interfere with the recognition phase of protein synthesis

33

What does chloramphenicol do?

It interferes with peptidyl transfer in translation

34

What are some examples of aminoglycosides?

Gentamicin
Tobramycin
Amikacin

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