Cell Wall Agents Flashcards
What are characteristics of cell wall agents?
- Affect some process in the synthesis of peptidoglycan
- Only active on growing cells
- Bactericidal
- Selective toxicity against bacteria
Which are the antibacterial drugs that target the cell wall?
- Beta lactan antimicrobials (Penicilins, cephalosporins, carbepenems, monobactams)
- Bacitracin
- Vancomycin
- Fosfomycin
- Ethambutol
What 2 rings do penicillins contain?
- thiazolidine ring
- beta lactam ring
What dictates the spectrum of activity and susceptibility to beta lactamase enzymes in penicillins?
The side chain
What is the method of action of penicillin?
Binds to and inhibits transpeptidase enzyme that forms peptide interbridge in peptidoglycan synthesis
What makes penicillins ineffective?
Beta lactamases which break up the beta lactam ring.
What are natural penicillins (G, V) active against and what are their characteristics?
Active against Gram + and limited activity against some Gram - cocci.
Pen G - degraded by stomach acid
Pen V - may be taken orally
Which penicillins are more effective on Gram - bacteria?
Broad spectrum (aminopenicillins), sensitive to beta lactamase
Which penicillin is more effective against Gram - rods?
Extended spectrum (anti-pseudomonal): mezlocillin, piperacillin
What are the characteristics of cephalosporins?
- 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
How many generations of cephalosporins are there?
5
Name a 4th and a 5th generation cephalosporin?
4th - Cefipime
5th - Ceftobiprole
Name other beta lactams
- Carbepenems/Carboxypenems
- Monobactams
Both very resistant to beta lactamases
What are the characteristics of Carbapenems?
- 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
What are the characteristics of Monobactams?
Aztreonam:
- effective against enteric bacteria
- Alternative for penicillin allergies
- effective against G - rods
- No activity against G + or obligate anaerobes
What are the properties of beta lactamase inhibitors?
- 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
Which are the non beta lactam peptides?
- Bacitracin
- Vancomycin
What are the characteristics of Bacitracin?
- 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
What are the characteristics of Vancomicin?
- 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)
