79 Questions
Which bacterial enzyme is responsible for the cross-linking of peptidoglycan molecules in the cell wall?
Transpeptidase
In what phase are penicillins bactericidal?
Growth and replication phase
Which class of penicillins is effective against gram-positive organisms and remains useful if the bacteria produce penicillinase?
Penicillinase-resistant penicillins
Which drug is an irreversible inhibitor of many bacterial β-lactamases?
Clavulanic acid
Why can high doses of penicillins lead to neurotoxicity?
They inhibit GABA receptors
What is the most common adverse effect of penicillins?
Hypersensitivity reaction
Which antibiotic has significant activity against anaerobes?
Cefepime
What is the specific inhibitor of renal peptidase that prolongs the half-life of imipenem and limits renal toxicity?
Cilastatin
Which antibiotic can cause tissue necrosis if given intramuscularly?
Vancomycin
What is the broad-spectrum antibiotic that is effective against gram-positive organisms, including MRSA?
Ceftaroline
Which antibiotic is specifically NOT effective against Pseudomonas aeruginosa?
Ceftaroline
Which antibiotic may lead to risk of fetal harm and nephrotoxicity?
Telavancin
What is the main characteristic of β-lactam antibiotics in terms of their selectivity?
They have a high degree of selective toxicity against bacteria because mammalian cells do not have cell walls.
What is the mechanism of action of penicillins?
Inhibition of bacterial cell wall synthesis
Why are β-lactam antibiotics able to selectively target bacteria?
They disrupt the formation of peptidoglycan in the bacterial cell wall.
What is the primary target of β-lactam antibiotics within bacterial cells?
Peptidoglycan synthesis
Which cellular feature makes β-lactam antibiotics ineffective against mammalian cells?
Absence of peptidoglycan in the cell membrane
What is the key factor contributing to the high selectivity of β-lactam antibiotics for bacteria over human cells?
Differences in cell wall composition
Which antibiotic binds to the P site of the 50S bacterial ribosomal subunit and blocks protein synthesis when a large amino acid or a polypeptide is in the P site?
Erythromycin
Which macrolide antibiotic is much better absorbed after oral administration than erythromycin?
Clarithromycin
Which macrolide antibiotic has the most unusual property of uptake into several tissues, maintaining high concentrations for prolonged periods?
Azithromycin
Which antibiotic binds to the σ subunit of RNA polymerase, leading to RNA polymerase entering a 'closed clamp' conformation and inhibiting transcription and translation?
Fidaxomicin
Which antibiotics bind to the 50S ribosomal subunit at or near the erythromycin site and have excellent activity against anaerobic bacteria?
Lincomycin and Clindamycin
Which antibiotic preferentially binds to the 30S subunit of the microbial ribosome, interfering with binding of amino acyl-tRNA and inhibiting chain elongation and termination?
Tetracyclines
What is the mechanism of action of tigecycline?
Reversibly binds to the 30S subunit of the microbial ribosome, inhibiting chain elongation and termination
Which antibiotic causes deposition in bones and teeth, leading to potential damage in developing teeth and bones?
Doxycycline
What distinguishes Amikacin from other aminoglycosides in terms of resistance?
It resists inactivation by many bacterial enzymes
What is the serious side effect associated with chloramphenicol?
Irreversible aplastic anemia
What is the main route of excretion for tetracyclines?
Bile/fecal
What is the primary reason tetracyclines limit absorption and cause damage to bones and teeth?
They form insoluble complexes with cations, limiting absorption and causing deposition in bones and teeth
Which enzyme is critical for chromosomal segregation in some bacterial strains?
DNA gyrase
What is the main mechanism of action of fluoroquinolones (Quinolones)?
Stabilization of DNA-enzyme complex
What effect does dietary calcium have on the absorption of Ciprofloxacin?
Reduces absorption
Which type of bacteria are usually less susceptible to fluoroquinolones?
Gram-positive
What is the clinical use of fluoroquinolones?
Prophylaxis and treatment of anthrax
What is the spectrum of fluoroquinolones?
Broad
What does DNA gyrase do in bacteria?
Introduces negative supercoils
"Gyrase Inhibitors e.g. Fluoroquinolones (Quinolones)" are primarily bacteriostatic or bacteriocidal?
"Bacteriocidal"
"Fluoroquinolones generally have good absorption and distribution, with the highest concentrations accumulating in:
"Urine"
Which enzyme is responsible for the cross-linking of peptidoglycan molecules in the bacterial cell wall?
Transpeptidase
Why are penicillins bactericidal when bacteria are in their growth and replication phase?
They inhibit cell wall synthesis by targeting transpeptidase
What is the main mechanism of development of hypersensitivity against penicillins?
Formation of immunogenic human protein-β-lactam hapten
Why can high doses of penicillins lead to neurotoxicity?
They bind to GABA receptors
Which enzyme do many bacteria produce to open the β-lactam ring and destroy the activity of penicillin antibiotics?
Penicillinase
What is the irreversible inhibitor of many bacterial β-lactamases?
Clavulanic acid
What is the primary target of β-lactam antibiotics within bacterial cells?
Cell wall synthesis
Why are β-lactam antibiotics able to selectively target bacteria?
They target cell wall synthesis unique to bacteria
Which enzyme is critical for chromosomal segregation in some bacterial strains?
DNA gyrase
What is the mechanism of action of tigecycline?
Inhibition of protein synthesis
Which antibiotic binds to the σ subunit of RNA polymerase, leading to RNA polymerase entering a 'closed clamp' conformation and inhibiting transcription and translation?
Rifampin
Which macrolide antibiotic has the most unusual property of uptake into several tissues, maintaining high concentrations for prolonged periods?
Azithromycin
What is the primary mechanism of action of tetracyclines?
Inhibition of protein synthesis by binding to the 30S subunit of the microbial ribosome
Which antibiotic is associated with a black box warning for acute pancreatitis and should only be used as a last resort?
Tigecycline
Which antibiotic has the potential to cause irreversible aplastic anemia, reversible bone marrow depression, and 'gray baby' syndrome in neonates?
Chloramphenicol
Which enzyme do aminoglycosides inhibit in bacteria?
Peptide synthetase
Which antibiotic has good penetration into cerebrospinal fluid, ocular fluids, and joint fluids due to its high lipid solubility?
Chloramphenicol
Which class of antibiotics bind to the P site of the 50S bacterial ribosomal subunit and block protein synthesis when a large amino acid or a polypeptide is in the P site?
Macrolides
Which antibiotic binds to the σ subunit of RNA polymerase, leading to RNA polymerase entering a 'closed clamp' conformation and inhibiting transcription and translation?
Fidaxomicin
What is the mechanism of action of chloramphenicol?
Block protein synthesis by binding to the P site of the 50S bacterial ribosomal subunit
What makes azithromycin unusual compared to other macrolide antibiotics?
It maintains high concentrations in tissues for prolonged periods
Which antibiotic has minimal absorption and remains mainly in the gastrointestinal tract, making its main clinical use in C. difficile infections?
Fidaxomicin
What is the primary target of tetracyclines within bacterial cells?
30S ribosomal subunit
Which antibiotic is chemically similar but pharmacologically different to erythromycin, and binds to the σ subunit of RNA polymerase?
Fidaxomicin
What is the mechanism of action of vancomycin?
Inhibition of peptidoglycan synthesis through binding to D-alanine-D-alanine terminus
Which antibiotic is specifically effective against Pseudomonas aeruginosa?
Cefepime
What is the primary mechanism of action of daptomycin?
Disruption of bacterial cell membrane integrity
What is the main spectrum of activity for aztreonam?
Mostly gram-negative bacteria
Which antibiotic has the broadest spectrum of all β-lactam antibiotics?
Imipenem
What is the specific inhibitor that prolongs the half-life of imipenem and limits its renal toxicity?
Cilastatin
What is the primary mechanism of action of gyrase inhibitors like fluoroquinolones?
Promoting double stranded breaks and inhibiting chromosomal segregation
Which enzyme is critical for chromosomal segregation in some bacterial strains?
Topoisomerase IV
Why are fluoroquinolones like ciprofloxacin generally not effective against gram-positive bacteria?
They inhibit DNA gyrase in gram-negative bacteria but Topoisomerase IV in gram-positive bacteria
What is the effect of dietary calcium on the absorption of ciprofloxacin?
It reduces the absorption of ciprofloxacin
What is the primary clinical use of fluoroquinolones like ciprofloxacin?
Treatment of urinary tract infections
What is the main characteristic of fluoroquinolones that allows for selective toxicity to bacteria over eukaryotic cells?
Their structural difference in bacterial vs eukaryotic topoisomerases
What is the most common adverse effect associated with fluoroquinolones like ciprofloxacin?
Neurotoxicity
Which type of bacteria are usually less susceptible to fluoroquinolones?
Gram-positive bacteria
What effect does high dietary calcium have on the excretion of ciprofloxacin?
It increases excretion of ciprofloxacin
Which bacterial enzyme can introduce negative supercoils into bacterial DNA?
DNA gyrase
Study Notes
Bacterial Cell Wall
- The enzyme responsible for cross-linking peptidoglycan molecules in the bacterial cell wall is transpeptidase.
Penicillins
- Penicillins are bactericidal during the growth and replication phase.
- Penicillinase-resistant penicillins are effective against gram-positive organisms and remain useful if the bacteria produce penicillinase.
- Clavulanate is an irreversible inhibitor of many bacterial β-lactamases.
- High doses of penicillins can lead to neurotoxicity.
- The most common adverse effect of penicillins is hypersensitivity.
- β-lactamases are produced by many bacteria to open the β-lactam ring and destroy the activity of penicillin antibiotics.
β-lactam Antibiotics
- Transpeptidase is the primary target of β-lactam antibiotics within bacterial cells.
- β-lactam antibiotics are able to selectively target bacteria because they inhibit cell wall synthesis.
- The key factor contributing to the high selectivity of β-lactam antibiotics for bacteria over human cells is the presence of peptidoglycan in bacterial cell walls.
Macrolide Antibiotics
- Azithromycin is a macrolide antibiotic with unusual properties, including uptake into several tissues, maintaining high concentrations for prolonged periods.
- Erythromycin is a macrolide antibiotic that binds to the P site of the 50S bacterial ribosomal subunit and blocks protein synthesis.
Other Antibiotics
- Tigecycline binds to the 30S subunit of the microbial ribosome, interfering with binding of amino acyl-tRNA and inhibiting chain elongation and termination.
- Tetracyclines bind to the 30S subunit of the microbial ribosome, interfering with binding of amino acyl-tRNA and inhibiting chain elongation and termination.
- Fluoroquinolones are gyrase inhibitors that inhibit DNA replication and transcription.
- Aminoglycosides inhibit protein synthesis by binding to the 30S subunit of the bacterial ribosome.
- Chloramphenicol binds to the 50S subunit of the bacterial ribosome, inhibiting protein synthesis.
- Vancomycin inhibits cell wall synthesis by binding to the terminal D-alanyl-D-alanine residue of peptidoglycan.
- Daptomycin inhibits bacterial cell membrane function.
- Aztreonam has a narrow spectrum of activity against gram-negative bacteria.
- Imipenem is a broad-spectrum β-lactam antibiotic.
- Cilastatin is a specific inhibitor that prolongs the half-life of imipenem and limits its renal toxicity.
Fluoroquinolones
- Gyrase is the bacterial enzyme that introduces negative supercoils into bacterial DNA.
- Fluoroquinolones are generally not effective against gram-positive bacteria.
- Dietary calcium decreases the absorption of ciprofloxacin.
- The primary clinical use of ciprofloxacin is against gram-negative bacteria.
- The main characteristic of fluoroquinolones that allows for selective toxicity to bacteria over eukaryotic cells is inhibition of DNA replication and transcription.
- The most common adverse effect associated with fluoroquinolones is gastrointestinal disturbance.
- Gram-positive bacteria are usually less susceptible to fluoroquinolones.
- High dietary calcium has no effect on the excretion of ciprofloxacin.
Test your knowledge on the mechanism of action of macrolide antibiotics, with a focus on erythromycin. Learn about the binding to the P site of the bacterial ribosomal subunit and its effect on protein synthesis. Explore the spectrum and properties of macrolide antibiotics.
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