A hospital isolate of Klebsiella pneumoniae is reported as resistant to gentamicin and tobramycin but susceptible to amikacin. The property of amikacin that best explains this retained susceptibility is:

• A It binds to the 50S ribosomal subunit instead of the 30S subunit
• B Its L-hydroxyaminobutyric acid side chain sterically hinders most aminoglycoside-modifying enzymes ✓
• C It is not transported into bacterial cells by oxygen-dependent uptake
• D It is unaffected by mutations in ribosomal proteins that affect other aminoglycosides

Explanation

Amikacin is a semisynthetic derivative of kanamycin bearing an L-hydroxyaminobutyric acid substituent. This bulky side chain sterically protects the molecule from modification by the majority of aminoglycoside-modifying enzymes, including most phosphotransferases and acetyltransferases that inactivate gentamicin and tobramycin. Amikacin still enters bacteria by the same oxygen-dependent transport and still acts on the 30S subunit, so options A and C are mechanistically wrong.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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