Final Exam - Cushman LOs Flashcards
Describe the structure of the peptidoglycan bridge in gram (+) and gram (-) cells
In gram (-) cells, the bridge exists between the DAP residue of one strand and the D-Ala of the other.
In gram (+) cells, the bridge exists between the L-Lys of one strand and the D-Ala of the other.
what cross-links the peptidoglycan strands?
a transpeptidase via a chemical reaction
beta lactam antibiotics MOA
inhibit transpeptidases that ‘glue’ the peptidoglycan strands together by cross-linking
-Beta lactams resemble D-Ala-D-Ala and the fool the transpeptidase into thinking that’s what it is
resistance mechanisms of B-lactam abx
-decreased cellular uptake of drug
-mutation of the penicillin-binding proteins (PBP) to decrease their affinity for penicillins
-efflux pump that pumps drug out of the cell
How does penicillin abx allergenicity occur?
-drug acts as hapten
-drug acylates host protein cells, which the raise Abs that result in allergic reaction
part that stabilizes the penicillin against hydrolysis under acidic conditions
electronegative substituents
-reason why Pen V is more stable (hydrolyzed less) in the stomach
more lipophilic side chains are more/less protein bound?
more
-more protein bound = less bioavailability because free concentration of drug is less
penicillins are primarily excreted by what route?
renal or biliary
penicillins are 10% excreted by what renal mechanism? 90% by what other mechanism?
10% - glomerular filtration
90% - tubular secretion
mechanism by which probenecid increases penicillin half life
competes for the tubular secretion mechanism
Pen G (benzylpenicillin) SOA
gram (+) cocci
what makes pen V more stable in acid than pen G?
electronegative ether oxygen
What is mecA?
the gene coding for methicillin resistance by MRSA
Ampicillin SOA
many gram (-) including:
-Salmonella
-Shegella
-proteus mirabilis
-E. coli
-H. flu
-Neisseria gonorrhoeae
how does ampicillin get into gram (-) cells?
Through the porins on the cell surface whose inner surface is hydrophilic and therefore transport charged molecules (like ampicillin)
Why does amoxicillin have better oral absorption than ampicillin?
a phenolic hydroxyl group has been added to the aromatic ring
MOA of B-lactamase inhibitors
they acylate the serine hydroxyl group in the active site of the B-lactamase
possible reason why pipericillin may be active against a broader spectrum of bacteria
resembles a longer portion of peptidoglycan than ampicillin does
-adds on to spectrum:
–pseudomonas aeruginosa
–Klebsiella pneumoniae
–Bacteroides fragilis
MOA of cephalosporins
same as penicillins
-reactions with transpeptidases (PBPs)
1st gen cephalosporins SOA and example
active against gram (+) cocci
-S. aureus and S. pyogenes
and group B streptococci
and strep pneumo
example: Cefazolin (IV), cephalexin (PO)
2nd gen cephalosporins SOA and example
same SOA as 1st gen but add gram (+) H. flu and gram (-) aceinetobacter, citrobacter, enterobacter, E. coli, Klebsiella, Neisseria, Proteus, Proidencia and Serratia
example: Cefuroxime (IV and PO)
