Which antibiotic listed is known to inhibit DNA synthesis?

Trimethoprim is recognized for its ability to inhibit DNA synthesis, particularly by targeting the bacterial enzyme dihydrofolate reductase, which is crucial in the folate synthesis pathway. This pathway is essential for the production of nucleic acids, including DNA. By inhibiting this enzyme, trimethoprim effectively hampers the formation of tetrahydrofolate and subsequently affects DNA replication and synthesis in susceptible bacteria.

In contrast, the other antibiotics listed have different mechanisms of action. Fusidic acid primarily functions by inhibiting bacterial protein synthesis by interfering with the translocation step in protein synthesis. Ceftriaxone is a beta-lactam antibiotic that disrupts bacterial cell wall synthesis rather than directly affecting DNA. Rifampicin, while known for its role in inhibiting RNA synthesis by binding to bacterial RNA polymerase, does not directly inhibit DNA synthesis.

Thus, trimethoprim stands out for its specific role in interfering with the synthesis of DNA through its effect on folate metabolism.