Tigecycline is a glycylcycline that overcomes tetracycline resistance. Its unique feature that bypasses the most common resistance mechanism is:
- A It is actively secreted into the periplasm by bacterial efflux pumps
- B It inhibits both the 50S and 30S ribosomal subunits simultaneously
- C Its bulky 9-t-butylglycylamido group sterically prevents binding to Tet efflux pump substrate site ✓
- D It binds to the peptidyl transferase centre rather than the A-site
Correct answer: C. Its bulky 9-t-butylglycylamido group sterically prevents binding to Tet efflux pump substrate site
Explanation
Tetracycline resistance in bacteria is primarily mediated by ribosomal protection proteins (RPPs) and efflux pumps (Tet A, B, C, etc.) that recognise and expel tetracyclines from the bacterial cell. Tigecycline has a bulky 9-t-butylglycylamido substituent at the C-9 position of the minocycline scaffold that sterically blocks its recognition by these Tet efflux pumps and prevents RPP binding. This allows tigecycline to reach the 30S ribosome even in resistant bacteria. It binds only the 30S 16S rRNA A-site, not the 50S.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.