Which of the following is NOT an example of an Aminoglycoside?

• A. Tobramycin
• B. Gentamicin
• C. Natamycin
• D. Amikacin

Answer: (C)

Aminoglycosides are a group of antibiotics that inhibit bacterial protein synthesis by binding to the 30S ribosomal subunit, leading to misreading of mRNA and a bactericidal effect. Tobramycin, gentamicin, and amikacin are classic members of this class and share that mechanism. Natamycin, on the other hand, is not an aminoglycoside. It’s a polyene antifungal that binds to ergosterol in fungal cell membranes, creating pores and disrupting membrane integrity rather than inhibiting bacterial protein synthesis. Because the question asks for an option that is not an aminoglycoside, natamycin is the correct choice. It’s used for fungal infections (such as fungal keratitis) rather than bacterial ones, reflecting its different mechanism of action.