A patient with multidrug-resistant tuberculosis is started on a regimen containing amikacin. Resistance to aminoglycosides via 16S rRNA methyltransferases is an emerging concern because this mechanism confers:
- A High-level resistance specifically to amikacin only
- B Broad high-level resistance to all clinically available aminoglycosides including amikacin ✓
- C Low-level resistance to all aminoglycosides except streptomycin
- D Resistance only when combined with an efflux pump
Correct answer: B. Broad high-level resistance to all clinically available aminoglycosides including amikacin
Explanation
16S rRNA methyltransferases (ArmA, Rmt family) add a methyl group to the aminoglycoside binding site on the 30S ribosomal subunit (G1405). Because virtually all aminoglycosides share this binding pocket, a single enzyme confers broad high-level resistance to gentamicin, tobramycin, amikacin, and streptomycin simultaneously. This is clinically devastating as it eliminates the entire class. Aminoglycoside-modifying enzymes (AMEs) typically affect subsets.
Reference: Lippincott Illustrated Reviews: Pharmacology, 7th ed.
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