Tigecycline, a glycylcycline, overcomes tetracycline resistance mediated by efflux pumps because:
- A The bulky N,N-dimethylglycylamido substituent at position 9 prevents recognition by the Tet efflux transporters ✓
- B It irreversibly binds the 50S ribosomal subunit instead of the 30S
- C Tigecycline inhibits bacterial DNA gyrase as an additional mechanism
- D It has an altered outer membrane transport mechanism not requiring OmpF porin
Correct answer: A. The bulky N,N-dimethylglycylamido substituent at position 9 prevents recognition by the Tet efflux transporters
Explanation
Classical tetracycline resistance involves either Tet efflux pumps (which actively expel the antibiotic) or ribosomal protection proteins. Tigecycline's 9-t-butylglycylamido modification at position 9 of minocycline creates steric bulk that is not recognised as a substrate by Tet(A)-Tet(E) efflux pumps and also overcomes ribosomal protection. It retains binding to the 30S ribosomal subunit (16S rRNA).
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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