The first plasmid-mediated, horizontally transmissible mechanism of colistin resistance in Enterobacterales was traced to which determinant?

• A pmrA/pmrB chromosomal mutation causing constitutive ArnBCADTEF expression
• B mcr-1 encoding a phosphoethanolamine transferase that modifies lipid A ✓
• C acrAB-tolC overexpression
• D tet(A) efflux determinant

Explanation

mcr-1, first reported in Escherichia coli from food animals, encodes a phosphoethanolamine transferase that adds phosphoethanolamine to lipid A of LPS, reducing polymyxin binding. Unlike classical colistin resistance, which arises from chromosomal mutations in two-component regulators (pmrAB, phoPQ) and cannot spread between organisms, mcr genes are carried on mobile elements and can disseminate horizontally, raising major public health concern given limited alternatives to polymyxins.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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