Introduction
The following quiz focuses on quinolones — a critical class of antibacterial agents studied in Advanced Pharmacology-II. It emphasizes their molecular mechanism of action, pharmacokinetic/pharmacodynamic relationships, and the major genetic and biochemical mechanisms that confer resistance. Questions are crafted for M.Pharm students and cover DNA gyrase and topoisomerase IV targeting, QRDR mutations, plasmid-mediated resistance (qnr, aac(6′)-Ib-cr, qepA, oqxAB), efflux and permeability changes, and laboratory/clinical implications of resistance. Use this set to test understanding of how quinolones kill bacteria, how resistance emerges and spreads, and how PK/PD principles guide dosing strategies to limit resistance development.
Q1. Which enzyme is the primary target of quinolones in Gram-negative bacteria?
- DNA gyrase (gyrA/gyrB)
- Topoisomerase IV (parC/parE)
- RNA polymerase
- Peptidoglycan transpeptidase
Correct Answer: DNA gyrase (gyrA/gyrB)
Q2. What is the principal bactericidal mechanism of quinolones?
- Inhibition of cell wall synthesis by preventing peptidoglycan cross-linking
- Stabilization of DNA–topoisomerase cleavage complexes leading to double-stranded DNA breaks
- Competitive inhibition of folate synthesis enzymes
- Disruption of the bacterial cell membrane via detergent-like action
Correct Answer: Stabilization of DNA–topoisomerase cleavage complexes leading to double-stranded DNA breaks
Q3. Which PK/PD index best correlates with quinolone efficacy and prevention of resistance?
- Time above MIC (T>MIC)
- Peak concentration to MIC ratio (Cmax/MIC)
- Area under the concentration–time curve to MIC ratio (AUC/MIC)
- Minimum bactericidal concentration (MBC)
Correct Answer: Area under the concentration–time curve to MIC ratio (AUC/MIC)
Q4. In many Gram-positive organisms (e.g., Streptococcus pneumoniae), the primary quinolone target at typical concentrations is:
- DNA gyrase
- Topoisomerase IV
- Ribosomal 30S subunit
- Cell wall autolysin
Correct Answer: Topoisomerase IV
Q5. Which of the following plasmid-mediated mechanisms protects DNA gyrase from quinolone binding?
- aac(6′)-Ib-cr acetyltransferase
- qnr-encoded pentapeptide repeat proteins
- oqxAB chromosomally encoded pump
- Mutated porin expression
Correct Answer: qnr-encoded pentapeptide repeat proteins
Q6. The aac(6′)-Ib-cr gene confers reduced susceptibility to certain fluoroquinolones by which mechanism?
- Pumping drug out of the cell via an efflux pump
- Acetylation of the quinolone molecule
- Altering the drug target through mutation
- Decreasing outer membrane porin expression
Correct Answer: Acetylation of the quinolone molecule
Q7. High-level quinolone resistance most commonly arises by which genetic process?
- Acquisition of single plasmid encoding a complete resistance pathway
- Stepwise accumulation of chromosomal point mutations in gyrA and then parC
- Loss of plasmids encoding susceptibility factors
- Overexpression of ribosomal protection proteins
Correct Answer: Stepwise accumulation of chromosomal point mutations in gyrA and then parC
Q8. Which plasmid-encoded gene is commonly associated with an efflux mechanism that reduces quinolone susceptibility?
- NorA
- QepA
- AcrAB
- gyrB
Correct Answer: QepA
Q9. A frequent mutation site in the quinolone resistance-determining region (QRDR) of gyrA in E. coli is substitution of which residue?
- Serine 83
- Glycine 45
- Lysine 65
- Alanine 120
Correct Answer: Serine 83
Q10. Induction of the bacterial SOS response during quinolone exposure contributes to resistance primarily by:
- Direct enzymatic degradation of the drug
- Increasing horizontal gene transfer and error-prone mutagenesis
- Enhancing outer membrane synthesis
- Stimulating peptidoglycan cross-linking
Correct Answer: Increasing horizontal gene transfer and error-prone mutagenesis
Q11. Which laboratory method is most definitive for identifying specific point mutations in gyrA or parC associated with quinolone resistance?
- Disk diffusion susceptibility testing
- DNA sequencing of the QRDR
- Culture on selective media
- Enzyme-linked immunosorbent assay (ELISA)
Correct Answer: DNA sequencing of the QRDR
Q12. The qnr proteins confer quinolone resistance by which of the following actions?
- Direct enzymatic degradation of fluoroquinolones
- Binding and protecting DNA–gyrase/topoisomerase complexes from quinolone inhibition
- Increasing drug efflux through the cell membrane
- Altering intracellular pH to inactivate the drug
Correct Answer: Binding and protecting DNA–gyrase/topoisomerase complexes from quinolone inhibition
Q13. Which statement best describes cross-resistance among fluoroquinolones?
- Resistance to one fluoroquinolone never affects others in the class
- Target site mutations often confer cross-resistance to multiple fluoroquinolones
- Plasma protein binding eliminates cross-resistance
- Cross-resistance only occurs with macrolides, not fluoroquinolones
Correct Answer: Target site mutations often confer cross-resistance to multiple fluoroquinolones
Q14. Coadministration of oral quinolones with divalent cation-containing antacids reduces oral absorption because:
- Divalent cations induce hepatic enzyme metabolism of quinolones
- Quinolones form insoluble chelate complexes with Mg2+/Ca2+, decreasing bioavailability
- Antacids increase intestinal motility and reduce contact time
- Antacids elevate gastric pH which chemically degrades quinolones
Correct Answer: Quinolones form insoluble chelate complexes with Mg2+/Ca2+, decreasing bioavailability
Q15. Which combination of resistance mechanisms most often results in the highest level of quinolone resistance?
- Single gyrA mutation combined with increased efflux or decreased permeability
- Single parC mutation alone
- Both gyrA and parC mutations together
- Only plasmid-mediated qnr without chromosomal mutations
Correct Answer: Both gyrA and parC mutations together
Q16. Which phenotypic test can suggest the presence of active efflux-mediated quinolone resistance?
- PCR amplification of parC
- Reduction in MIC when tested in the presence of an efflux pump inhibitor
- Observation of swarming motility on agar
- Latex agglutination assay for qnr proteins
Correct Answer: Reduction in MIC when tested in the presence of an efflux pump inhibitor
Q17. Which gene encodes an acetyltransferase that can modify and reduce susceptibility to ciprofloxacin?
- qnrA
- aac(6′)-Ib-cr
- gyrA
- parC
Correct Answer: aac(6′)-Ib-cr
Q18. Quinolones are classified pharmacodynamically as:
- Bacteriostatic agents
- Bactericidal agents
- Fungistatic agents
- Virucidal agents
Correct Answer: Bactericidal agents
Q19. The post-antibiotic effect (PAE) of quinolones refers to:
- The immediate bactericidal activity during drug exposure
- Persistent suppression of bacterial growth after drug concentrations fall below the MIC
- Enzymatic inactivation of the drug by bacteria
- Increased mutation rate during drug exposure
Correct Answer: Persistent suppression of bacterial growth after drug concentrations fall below the MIC
Q20. Which dosing strategy is most likely to minimize selection of quinolone-resistant mutants?
- Low daily doses for prolonged periods to reduce toxicity
- High-dose, short-duration regimens that achieve optimal AUC/MIC targets
- Intermittent subtherapeutic dosing to allow immune clearance
- Using quinolones only as topical agents
Correct Answer: High-dose, short-duration regimens that achieve optimal AUC/MIC targets
