Antimicrobial Agents and Resistance: Part Two

Question 1

Which antibiotics are in the β-lactam family?

Answer 1

• Penicillins (numerous)
• Cephalosporins (numerous)
• Carbapenams (imipenem, meropenem)
• Monobactams (aztreonam)

Question 2

Which NON β-lactam antibiotics inhibit cell wall synthesis?

Answer 2

• Glycopeptides (vancomycin)
• Polypeptides (bacitracin)

Question 3

How do β-lactam antibiotics work?

Answer 3

• β -lactam ring binds to and inhibits the enzyme transpeptidase (also known as Penicillin-Binding Protein=PBP) that cross-links the peptidoglycan chains to form the cell wall
• The antibiotic causes cytolysis due to the weakening of the cell wall that makes the bacterium susceptible to osmotic pressure

Question 4

β -lactamases (also called penicillinases)

Answer 4

cleave the β -lactam ring

Question 5

How did MRSA form?

Answer 5

the bacteria mutated the attachment site of the antibiotic

Question 6

Vancomycin

Answer 6

• is a complex glycopeptide), disrupts cell wall peptidoglycan of Gram-positive bacteria.
• Inactive against Gram-negative bacteria: the molecule is too large to pass through the outer membrane pores.

Question 7

Polymyxins

Answer 7

• target Gram-negative bacteria
• Cyclic polypeptides with a hydrophobic tail produced by a Gram- positive organism (Bacillus polymyxa). Inserts into the cell membrane of Gram negative bacteria and increases permeability leading to cell death.
• Binds to LPS.

Question 8

Quinolones

Answer 8

• a family of antibiotics that target the enzyme DNA gyrase
• This enzyme introduces negative supercoils into bacterial DNA so that it can be packaged into the bacterial cell during cell division. If DNA gyrase is impaired by these antibiotics, replication halts. Bactericidal.

Question 9

Rifampicin

Answer 9

• targets the beta subunit of RNA polymerase and inactivates this subunit. When this occurs, transcription halts and the cells cannot make RNA.
• Bactericidal.

Question 10

sulfonamides

Answer 10

• competitive inhibitor of dihydropteroate synthetase for folic acid metabolism

Question 11

Aminoglycosides

Answer 11

(broad spectrum Gram + and -, bactericidal), attach irreversibly to bacterial ribosomes

Question 12

Chloramphenicol

Answer 12

(broad spectrum Gram + and -, bacteriostatic), it diffuses into the nervous system and is thus useful to treat meningitis.

Question 13

Tetracyclines

Answer 13

(broad spectrum, bacteriostatic) It works by binding reversibly to the subunit 30S ribosome.

Question 14

Macrolides

Answer 14

(broad spectrum, bacteriostatic) Bind reversibly to the subunit 50S of the ribosome.

Question 15

The mechanisms of Antibiotic Resistance

Answer 15

• Reduced Permeability
• Active export of the antibiotic (Efflux pump)
• Antibiotic Inactivation
• Target alteration