14-Antimicrobials

Question 1

Beta lactam antibiotics act on

Answer 1

the cell wall

Question 2

Explain beta-lactams and their mechanism of resistance?

Answer 2

• in the absence of beta-lactam antibiotics, transpeptidases also known as penicillin binding proteins catalyse the cross links between glycan changes in the peptidoglycan
• covalent bonds are created between the peptide and sugar chains that create a rigid cell wall that protects the bacterial cell from osmotic forces that can result in cell rupture.
• beta-lactam antibiotics, are similar to the natural peptidoglycan subunits (D-ala-D-ala) that are the substrate for the transpeptidases.
• these antibiotics bind strongly to the active site in the transpeptidase and stop cell wall synthesis.

Question 3

what do penicillin, carapenems, cephalosporins and monobactams all have in common?

Answer 3

the beta lactam ring

Question 4

what is the importance attributed to the beta lactam ring

Answer 4

it mimics the shape of the terminal D-ala-d-ala peptide sequence that is the substrate for the transpeptidase.

Question 5

what are the advantages releated to synthetic beta lactams?

Answer 5

greater spectrum of acitivity, greater resistance to beta lactamases as well as different pharamcokenetic properties

Question 6

What are the four main general resistance mechanisms to beta lactams

Answer 6

1. penetration
2. porins
3. pumps
4. peptiglycan absent

Question 7

explain what is penetration, porins, pumps and peptiglycan absent as a means to resist beta-lactams

Answer 7

1. penetration: intracellular bacteria are resistant to beta lactam if they are in a mamamalian cell
2. porins: gram neg bacteria are resistant to beta lactams since the outer cell membrane protects the peptidoglycan but porins can allow beta lactams inside. however, some gram negatives have smaller porins that excludes beta lactams.
3. pumps; gram neg express abc transporters to pump antibiotics out of the cell
4. peptidoglycan is absent - some bacteria like mycobacteria lack a cell wall and thus are not affected by beta lactam antibiotics

Question 8

antibiotics can attack what parts of the cell?

Answer 8

1. dna
2. ribosomes
3. cell wall

Question 9

what happens to ribosomes when they become attacked by antibiotics?

Answer 9

they stop protein synthesis

bacteriastatic effect - no growth

Question 10

what happens when antibiotics attack bacteria dna

Answer 10

-bactericial; death