Cell Wall Agents

Question 1

What are characteristics of cell wall agents?

Answer 1

• Affect some process in the synthesis of peptidoglycan
• Only active on growing cells
• Bactericidal
• Selective toxicity against bacteria

Question 2

Which are the antibacterial drugs that target the cell wall?

Answer 2

• Beta lactan antimicrobials (Penicilins, cephalosporins, carbepenems, monobactams)
• Bacitracin
• Vancomycin
• Fosfomycin
• Ethambutol

Question 3

What 2 rings do penicillins contain?

Answer 3

• thiazolidine ring

- beta lactam ring

Question 4

What dictates the spectrum of activity and susceptibility to beta lactamase enzymes in penicillins?

Answer 4

The side chain

Question 5

What is the method of action of penicillin?

Answer 5

Binds to and inhibits transpeptidase enzyme that forms peptide interbridge in peptidoglycan synthesis

Question 6

What makes penicillins ineffective?

Answer 6

Beta lactamases which break up the beta lactam ring.

Question 7

What are natural penicillins (G, V) active against and what are their characteristics?

Answer 7

Active against Gram + and limited activity against some Gram - cocci.
Pen G - degraded by stomach acid
Pen V - may be taken orally

Question 8

Which penicillins are more effective on Gram - bacteria?

Answer 8

Broad spectrum (aminopenicillins), sensitive to beta lactamase

Question 9

Which penicillin is more effective against Gram - rods?

Answer 9

Extended spectrum (anti-pseudomonal): mezlocillin, piperacillin

Question 10

What are the characteristics of cephalosporins?

Answer 10

• Resistant to inactivation by certain beta lactamases (e.g. S. aureus)
• Classified into generations based on susceptibility to beta lactamases, potency, spectrum
• Contain 2R groups (vs penicillins that contain 1 ring and the same two rings) that determine pharmacological properties
• Beta lactam ring and dihydrothiazine ring

Question 11

How many generations of cephalosporins are there?

Answer 11

5

Question 12

Name a 4th and a 5th generation cephalosporin?

Answer 12

4th - Cefipime

5th - Ceftobiprole

Question 13

Name other beta lactams

Answer 13

• Carbepenems/Carboxypenems
• Monobactams
  Both very resistant to beta lactamases

Question 14

What are the characteristics of Carbapenems?

Answer 14

• Active against almost everything (almost all G+ except MRSA)
• Very low concentrations required
• Poor oral bioavailability (given IV)
• Often used for P. Aeruginosa and Enterococcus infections
• Can cause seizures

Question 15

What are the characteristics of Monobactams?

Answer 15

Aztreonam:

• effective against enteric bacteria
• Alternative for penicillin allergies
• effective against G - rods
• No activity against G + or obligate anaerobes

Question 16

What are the properties of beta lactamase inhibitors?

Answer 16

• Allows beta lactam antibiotics to be more effective
• Have little antimicrobial activity and must be combined with beta lactam antibiotic
• Clavulanic acid, Tazobactam
• Combinations in a single pill: Clavulanic acid + Amoxicillin = Augmentin

Question 17

Which are the non beta lactam peptides?

Answer 17

• Bacitracin

- Vancomycin

Question 18

What are the characteristics of Bacitracin?

Answer 18

• Prevents transport of peptidoglycan precursors (NAM & NAG) across the cytoplasmic membrane where they are assembled and cross linked
• Toxicity limits it to topical use
• Found in antibiotic ointments such as Neosporin

Question 19

What are the characteristics of Vancomicin?

Answer 19

• Effective against MRSA, MRSE, and MDRSP
• Given IV (oral for intestinal infections such as C. difficile)
• Prevents cross linking between NAM subunits of the peptidoglycan (prevents the formation of the inter bridge of gram + cells)