Flashcards in Bacterial Cell Wall and Beta Lactam Antibiotics Deck (43)
Color of gram (+) bacteria under gram stain?
Color of gram (-) bacteria under gram stain?
How do gram (+) and gram (-) bacteria differ?
differ in the structures of their cell walls
How can some drugs get into gram (-) bacteria?
through the porins in the outer membrane
Is the peptidoglycan layer thicker in gram (-) or gram (+) bacteria?
much thicker in gram (+) bacteria
How many membranes do gram (+) bacteria have?
How many membranes do gram (-) bacteria have?
two membranes - inner and an outer membrane
What enzyme cross-links the peptidoglycan strands?
Describe the beta-lactam antibiotic mechanism of action.
inhibition of transpeptidases that "glue" the peptidoglycan strands together by cross-linking
Why do the bacterial transpeptidases not catalyze reactions with host cell proteins?
the bacterial substrate contains unnatural D-Ala amino acid residues that are not found in the host cell proteins
Name three ways resistance to beta-lactam antibiotics can develop.
1. decreased cellular uptake of the drug
2. mutation of the penicillin-bindin gproteins to decrease their affinity for penicillins
3. the presence of an efflux pump that pumps the antibiotic out of the cell
Most common mechanism of resistance to beta-lactam antibiotics
induction or elaboration of bacterial beta-lactamases
Describe the reaction that beta-lactamaes catalyze.
the hydrolysis of the beta-lactam moiety
The allergenicity of beta-lactam antibiotics results from?
the drug acting as a hapten, acylates host cell proteins, which raise antibodies and cause an allergic reaction
Can a person who has demonstrated an allergy to one penicillin be given another penicillin?
No, because cross-sensitivity is common.
What should be kept away from penicillin solutions?
heavy metal ions (they catalyze penicillin degradation reactions)
Which routes are penicillins rapidly excreted by?
the renal or biliary routes
10% of renal excretion of penicillins is by?
90% of renal excretion of penicillins is by?
What happens when probenecid is administered along with penicillin?
The anionic penicillin competes with the anion probenecid for the tubular secretion mechanism in the kidneys - causes an increase in the half life of penicillin
Benzylpenicillin (Penicillin G) antimicrobial spectrum:
Gram (+) cocci + Neisseria gonorrhoeae and Haemophilus influenza [both gram (-)]
Is Benzylpenicillin (Penicillin G) beta-lactamase sensitive?
Precautions when using Penicillin G (Benzylpenicillin)
Pen G should be used with caution in individuals with histories of significant allergies and/or asthma
What drug is the drug of choice for treatment of more infections than any other antibiotic?
Is Methicillin beta-lactamase sensitive?
Why must methicillin be administered by injection?
it is unstable to acid in the stomach
What's the antibiotic spectrum of methicillin?
narrow. It is primarily for treatment of beta-lactamase-producing Staphylococcus aureus
Why is MRSA resistant to Methacillin?
because of a mutation in the penicillin-binding protein (transpeptidase) - methicillin resistance gene (mecA)
What kind of antibiotic is Cephapirin?
a cephalosporin antibiotic