Which antibiotic is known to inhibit RNA synthesis?

Rifampin is known to inhibit RNA synthesis, making it the correct choice. This antibiotic functions by binding to the bacterial enzyme RNA polymerase, which is essential for the transcription process in bacteria. By inhibiting this enzyme, rifampin effectively prevents the synthesis of RNA, thereby interfering with bacterial growth and replication. It is particularly useful against specific infections such as tuberculosis, where it serves as a critical component of combination therapy.

The other options do not inhibit RNA synthesis. Cephalosporins and beta-lactams primarily target bacterial cell wall synthesis, disrupting the structural integrity of the bacterial cell and leading to cell lysis. Aminoglycosides, on the other hand, inhibit protein synthesis by binding to the ribosomal 30S subunit, preventing the initiation of translation. Each of these antibiotic classes has a distinct mechanism of action, which is different from the inhibition of RNA synthesis seen with rifampin.