Linezolid is bacteriostatic against most gram-positive organisms but bactericidal against Mycobacterium tuberculosis. Its mechanism of action is:
- A Inhibiting peptidyl transferase activity at the P-site of the 50S ribosome like macrolides
- B Binding to the 23S rRNA of the 50S ribosomal subunit, preventing formation of the 70S initiation complex and blocking translation initiation ✓
- C Binding the 16S rRNA of the 30S subunit, causing mistranslation and misfolded protein accumulation
- D Preventing translocation of peptidyl-tRNA from A-site to P-site like fusidic acid
Correct answer: B. Binding to the 23S rRNA of the 50S ribosomal subunit, preventing formation of the 70S initiation complex and blocking translation initiation
Explanation
Linezolid, an oxazolidinone, uniquely binds to domain V of 23S rRNA in the 50S subunit at the P-site and A-site interface. This prevents proper 70S initiation complex assembly (inhibiting the joining of 30S and 50S subunits around the initiator fMet-tRNA), thus blocking the very first step of translation. This mechanism is completely unique among antibiotics, with no cross-resistance to other classes targeting the ribosome. Macrolides bind 50S at the peptide exit tunnel; aminoglycosides bind 30S (16S rRNA).
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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