A patient with recurrent Enterococcus faecium bacteraemia is treated with high-dose daptomycin. After two weeks, the isolate shows a daptomycin MIC that has risen eightfold. The most likely laboratory finding underlying this change is:

• A Hydrolysis of daptomycin by a cyclic lipopeptidase
• B Acquisition of the mecA gene on SCCmec
• C Loss of porin channels in the cell wall
• D Mutations in liaFSR and other genes altering membrane phospholipid homeostasis ✓

Explanation

Daptomycin inserts into the bacterial cytoplasmic membrane and disrupts ion gradients. Resistance in enterococci emerges through regulatory mutations involving the LiaFSR three-component system and related pathways that remodel membrane phospholipid composition, redistributing cardiolipin away from the division septum where daptomycin acts. No degrading enzyme exists, enterococci lack gram-negative porins, and mecA is irrelevant outside staphylococci.

Reference: Mandell, Douglas and Bennett's Principles and Practice of Infectious Diseases, 9th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.