Antimicrobial Mechanisms 2

Question 1

What are the features outside of a bacteria cell?

Answer 1

Cell wall and cell membrane

Question 2

What two monosaccharide units make up the peptidoglycan cell wall?

Answer 2

NAM
NAG

Question 3

What does transpeptidases do?

Answer 3

Transpeptidase is a membrane-bound enzyme that catalyses peptide cross-linking between two adjacent peptidoglycan cell walls.

Question 4

What are the features of a gram +ve bacteria cell wall?

Answer 4

Thick
strong
porous
drugs can penetrate to the cell membrane

Question 5

What are the features of a gram -ve cell wall?

Answer 5

Thin wall
additional outer membrane- provides barrier to cell wall and inner membrane

Question 6

What is the purpose of a cell wall?

Answer 6

Protect cell membranes from rupture and helps maintain the shape of the cell

Question 7

What is the ideal bond angle in beta-lactam ring

Answer 7

120 degrees

Question 8

Process of cell wall synthesis

Answer 8

serine residue on enzyme transpeptidase attacks beta-lactam ring and acylates enzyme, transpeptidase now inactive, which prevents the formation of structural cross-linking in bacterial cell wall, cell weakened, bursts and dies

Question 9

What do beta-lactamases do

Answer 9

Inactivate the beta lactam ring

Question 10

What are the aims of drug development for penicillin G

Answer 10

• increase acid stability for oral administration
• increase resistance to beta-lactamases
• increase spectrum of activity

Question 11

Name two beta-lactamase resistant drugs

Answer 11

amoxycillin
methicillin

Question 12

What can prevent beta-lactamases from opening the beta-lactam ring but retain binding to transpeptidase

Answer 12

Larger side chains

Question 13

Isoxazoyl penicillins have good activity against which penicillin resistant infection

Answer 13

Streptococcal aureus

Question 14

95% of hospitals detected S. aureus strains are now insensitive to which drug

Answer 14

methicillin

Question 15

Which groups favour inhibition of gram +ve bacteria

Answer 15

Hydrophobic

Question 16

Which groups favour inhibition of gram -ve bacteria

Answer 16

Hydrophilic (best if group is attached to carbon to carbonyl)

Question 17

What antibiotic is biosynthesised by the exapndase enzyme?

Answer 17

cephalosporins

Question 18

cephalosporins have good activity against which type of baterial infections?

Answer 18

Gram negatvie

Question 19

Fourth generation are…

Answer 19

zwitterionic

Question 20

What is the benefit of zwitterion in cephalosporins?

Answer 20

enhances ability to cross outer membrane of gram -ve bacteria

Question 21

carbapenems target which kind of bacteria

Answer 21

broad spectrum

Question 22

monobactams target gram +ve or gram -ve bacteira?

Answer 22

gram -ve

Question 23

What is the role of clavulanic acid?

Answer 23

It is an irreversible beta-lactamase inhibitor, it binds to the beta-lactamase active site and inactivates the enzyme which means it cannot open the beta-lactam ring which enhances the effect of antimicrobials.

Question 24

What class of antibiotic is vancomycin in?

Answer 24

glycopeptide

Question 25

How does vancomycin work?

Answer 25

forms stable hydrogen bonded dimer
inserts between peptidoglycan, forces peptides away so cannot cross-link
cell bursts and lyses

Question 26

Which type of bacterial infections is Vancomycin used for?

Answer 26

Gram +ve bacteria only, cannot cross gram -ve cell membrane

Question 27

Why does vancomycin need to be injected?

Answer 27

does not cross gut membrane

Question 28

What antibiotic targets the cell membrane?

Answer 28

Gramidicin A

Question 29

How does gramicidin work?

Answer 29

forms an ion channel across cell wall in gram +ve bacteria

Question 30

What is gramicidin A used to treat?

Answer 30

used in topical medicines to treat infected wounds e.g. eye drops