Ethambutol exerts its antimycobacterial effect by inhibiting which step in mycobacterial cell wall synthesis?

• A Synthesis of D-alanine by alanine racemase
• B Synthesis of mycolic acids by fatty acid synthase II
• C Cross-linking of peptidoglycan by transpeptidases
• D Polymerization of arabinogalactan by arabinosyl transferases ✓

Explanation

Ethambutol specifically inhibits arabinosyl transferases (embAB operon) that polymerize arabinan chains of arabinogalactan, a key component of the mycobacterial cell wall core. This disrupts the mycolyl-arabino-galactan-peptidoglycan complex. Resistance arises from embB mutations, particularly at codon 306. This mechanism is unique to ethambutin among first-line anti-TB drugs.

Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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