Which agent is a tetracycline antibiotic?

• A. Amoxicillin
• B. Minocycline
• C. Rifampicin
• D. Co-Trimoxazole

Answer: (B)

Tetracyclines inhibit bacterial protein synthesis by reversibly binding to the 30S ribosomal subunit, blocking the attachment of aminoacyl-tRNA and preventing elongation. This mechanism gives broad coverage and a bacteriostatic effect, especially against Gram-positive, Gram-negative, and atypical organisms. Among the options, minocycline is a tetracycline antibiotic, sharing the same mechanism and class as other drugs like doxycycline. The other agents belong to different classes: amoxicillin is a beta-lactam that inhibits cell wall synthesis, rifampicin inhibits RNA polymerase, and co-trimoxazole blocks folate synthesis.