Antibiotics II/III Flashcards
What is the binding site for all penicillins and first generation cephalosporins?
PBP 2b
What is the binding site for all other cephalosporins, carbapenems and monobactams?
PBP 2x
How do PBPs function?
They anchor and orient the native bacterial transpeptidase with the lactam ring.
How do you prevent penicillin from hydrolysis?
Place large aromatic groups around the ring to sterically hinder access of penicillinase.
How do you prevent amino and extended spectrum penicillins from hydrolysis?
Combine them with a suicide inhibitor, which will also extend their antibaterial spectrum.
What is responsible for virtually all cases of lactam allergy?
The 5 or 6 member ring adjacent to the lactam structure.
What are the two types of lactam allergies?
Anaphylaxis (hives, hypotension, angioedema, respiratory stridor) = IgE
Maculopapular rash = IgM
What is the antibacterial spectrum of lactams?
Skin and soft tissue infections with beta hemolytic Streptococcal species.
How are penicillins and their cephalosporin counterparts similar and different?
Both have identical efficacy.
Penicillins are more active and cephalosporins have a broader spectrum of antibacterial activity.
What is the coverage of Carbapenems?
Broad gram positive (except MRSA) and gram negative
What is the coverage of Monobactams?
Only gram negatives.
How does vancomycin work?
it competes with L-alanine and inhibits the racemase responsible for the conversion of L-alanine to R-alanine.
How does lactate contribute to vancomycin resistance?
Alanine and lactic acid both have a 3 carbon structure.
Increased lactate concentration results in increased lactone, which substitutes alanine, so that vancomycin cannot bind to it.
What is the spectrum of activity for Vancomycin?
Serious infections from gram positive organisms that are resistant to lactams.
- MRSA
- Staph epidermidis
- Enterococcus (ampicillin resistant group D strep Faecalis)
- Pneumococcal meningitis
- Metronidazole resistant strains of C. difficile
How do daptomycin and polymixins work?
Insertion of a lipophilic tail through the teichoic acid backbone of a the cell membrane in gram positive (daptomycin) and gram negative (polymixin) bacteria, resulting in leakage of intracellular ions to the extracellular space.
