Which statement accurately describes the mechanism of tigecycline resistance in Acinetobacter baumannii?

• A Overexpression of the RND-type efflux pump AdeABC is the primary mechanism of tigecycline resistance in A. baumannii ✓
• B Tigecycline resistance is caused exclusively by target site modification (ribosomal methylation)
• C Enzymatic inactivation of tigecycline by tetracycline-modifying enzymes is the main mechanism
• D Outer membrane impermeability is the sole mechanism

Explanation

Tigecycline is a glycylcycline that was designed to overcome classical tetracycline resistance mechanisms (efflux and ribosomal protection). However, in A. baumannii, overexpression of the chromosomal AdeABC efflux pump (a resistance-nodulation-division/RND-type tripartite efflux system) effectively reduces intracellular tigecycline concentrations. AdeABC overexpression is regulated by the two-component system AdeRS and can arise by mutations in adeRS. Additionally, AdeIJK and AdeFGH efflux pumps contribute. Ribosomal methylation by Tet(X) enzymes (tigecycline-modifying monooxygenases found in some Enterobacteriaceae) is not the primary mechanism in A. baumannii.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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