Question

The fluoroquinolones act by:

• A. \( \text{Inhibiting folic acid synthesis, reducing nucleotide production and DNA synthesis} \)
• B. Inhibiting DNA gyrase and topoisomerase IV, causing supercoiling and fragmentation of bacterial DNA
• C. \( \text{Disrupting peptidoglycan cross-linking, weakening the bacterial cell wall} \)
• D. \( \text{Inhibiting ribosomal subunits, leading to the cessation of protein synthesis} \)

Hint:

Fluoroquinolones, such as ciprofloxacin and levofloxacin, are commonly used to treat bacterial infections. Their unique target, DNA gyrase, makes them effective against both Gram-positive and Gram-negative bacteria.

Answer 1

The Correct Option is B

Antibiotics generally attack one of four bacterial targets, the cell wall, the ribosome, a metabolic pathway, or the DNA-replication machinery. Sorting fluoroquinolones into the right bucket answers this question.

1. Folic acid synthesis inhibition: A metabolic pathway target used by sulfa drugs, starving the bacterium of the building blocks it needs for nucleotides, not the fluoroquinolone target.
2. DNA gyrase and topoisomerase IV inhibition: These two enzymes relieve the twisting stress that builds up in bacterial DNA as it unwinds for replication. Fluoroquinolones trap the enzymes mid-action on the DNA strand, leaving it supercoiled and broken, which is the defining mechanism of this drug class.
3. Peptidoglycan cross-linking disruption: A cell wall target, the domain of penicillins and cephalosporins, structurally unrelated to how fluoroquinolones work inside the cell.
4. Ribosomal subunit inhibition: A protein synthesis target used by tetracyclines and aminoglycosides, again a different cellular process from DNA replication.

Fluoroquinolones are specifically the DNA-replication-machinery class of antibiotics, acting through DNA gyrase and topoisomerase IV rather than the wall, ribosome, or folate pathway. The correct answer is Inhibiting DNA gyrase and topoisomerase IV, causing supercoiling and fragmentation of bacterial DNA.