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

Step 1: Mechanism of fluoroquinolones. Fluoroquinolones are a class of broad-spectrum antibiotics that target bacterial enzymes involved in DNA replication. Specifically, they inhibit DNA gyrase and topoisomerase IV, which are essential for relieving supercoiling tension during DNA replication and transcription. 

Step 2: Effects of inhibition. By inhibiting these enzymes, fluoroquinolones prevent bacterial DNA from properly unwinding and replicating. This results in supercoiling, DNA fragmentation, and ultimately bacterial cell death. 

Step 3: Comparison with other options. - Option \( (A) \): Describes the mechanism of sulfonamides and trimethoprim. 
- Option \( (C) \): Refers to the action of beta-lactam antibiotics (e.g., penicillins). 
- Option \( (D) \): Refers to antibiotics like tetracyclines and aminoglycosides. 

Conclusion: The correct answer is \( (B) \).