Final answer:
Ciprofloxacin inhibits the activity of DNA gyrase, an enzyme crucial for bacterial DNA replication, and belongs to the fluoroquinolones class of antimicrobials.
Step-by-step explanation:
Among the options provided, Ciprofloxacin is an antimicrobial that inhibits the activity of DNA gyrase. DNA gyrase, or topoisomerase type II, is an enzyme essential for DNA replication in bacteria. Ciprofloxacin, a member of the fluoroquinolones class of synthetic antimicrobials, blocks the DNA unwinding process necessary for bacterial DNA replication. This action provides for their effectiveness against a broad spectrum of gram-positive and gram-negative bacteria. Nalidixic acid was the first quinolone discovered which specifically inhibits bacterial DNA gyrase, and the fluoroquinolones like ciprofloxacin were developed as more potent successors.