Which of the following does NOT inhibit the 50S ribosomal subunit?

Which of the following does NOT inhibit the 50S ribosomal subunit?

• A. Macrolides
• B. Ceftriaxone
• C. Lincomycin
• D. Chloramphenicol

Answer: (B)

The main idea here is which antibiotics interfere with the 50S ribosomal subunit. Drugs that bind to 50S disrupt protein synthesis—macrolides block the translocation step, chloramphenicol inhibits the peptidyl transferase center, and lincomycin also interferes with peptide bond formation on the 50S subunit. Ceftriaxone, however, is a beta-lactam antibiotic that targets bacterial cell wall synthesis by inhibiting penicillin-binding proteins; it does not affect the ribosome at all. Therefore, it does not inhibit the 50S subunit.

The main idea here is which antibiotics interfere with the 50S ribosomal subunit. Drugs that bind to 50S disrupt protein synthesis—macrolides block the translocation step, chloramphenicol inhibits the peptidyl transferase center, and lincomycin also interferes with peptide bond formation on the 50S subunit. Ceftriaxone, however, is a beta-lactam antibiotic that targets bacterial cell wall synthesis by inhibiting penicillin-binding proteins; it does not affect the ribosome at all. Therefore, it does not inhibit the 50S subunit.