Which antibiotic class predominantly inhibits bacterial protein synthesis at the 30S ribosomal subunit?

• A. Macrolides.
• B. Tetracyclines.
• C. Beta-lactams.
• D. Aminoglycosides (e.g., gentamicin) primarily, with tetracyclines also targeting 30S.

Answer: (D)

The key idea is identifying which antibiotic class mainly blocks protein synthesis by binding to the 30S ribosomal subunit. Aminoglycosides, such as gentamicin, bind irreversibly to the 30S subunit and cause misreading of mRNA, leading to faulty proteins and bacterial death. They are bactericidal and require oxygen for uptake. Although tetracyclines also target the 30S by reversibly blocking tRNA binding to the A site, their effect is typically bacteriostatic and they’re considered a secondary 30S inhibitor. Other classes act on different targets: macrolides affect the 50S subunit to block translocation, and beta-lactams inhibit cell wall synthesis. So the class most characteristically associated with 30S inhibition and bactericidal action is aminoglycosides.