Acquisition of Daptomycin Resistance by Enterococcus faecium Confers Collateral Sensitivity to Glycopeptides

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Daptomycin is a critical last-line antibiotic for treating multidrug-resistant Enterococcus faecium infections.
• The emergence of daptomycin-resistant E. faecium strains poses a significant clinical challenge.
• Understanding the mechanisms of resistance and potential evolutionary trade-offs, such as collateral sensitivity, is crucial.

Purpose of the Study:

• To investigate the evolution and mechanisms of daptomycin resistance in clinical E. faecium isolates.
• To identify collateral sensitivity (CS) as an evolutionary trade-off during the acquisition of daptomycin resistance.
• To explore the potential for novel therapeutic strategies combining daptomycin and glycopeptides.

Main Methods:

• Evolved daptomycin resistance in six daptomycin-susceptible E. faecium isolates to generate resistant mutants.
• Assessed fitness costs (growth, competition, virulence) associated with daptomycin resistance.
• Analyzed genetic mutations (e.g., in liaFSR, yycFG, cls), cell wall characteristics, and gene expression (dltABCD, tagGH, vanA cluster).
• Utilized in silico analyses to investigate transposon formation and gene disruption.

Main Results:

• All six E. faecium strains acquired high-level daptomycin resistance in vitro, accompanied by significant fitness costs.
• Observed mutations in liaFSR, yycFG, and cls, increased cell surface positive charge, thicker cell walls, and altered expression of dltABCD and tagGH.
• Discovered a novel collateral sensitivity to glycopeptides in one resistant isolate (SC1762-D) due to disruption of the vanA gene cluster by an IS1216E-based composite transposon.
• A non-CS resistant mutant (SC1174-D) exhibited upregulation of the vanA gene cluster.

Conclusions:

• Daptomycin resistance in E. faecium is associated with fitness costs and specific genetic and cellular alterations.
• A novel collateral sensitivity between daptomycin resistance and glycopeptide sensitivity was identified in E. faecium.
• Findings provide a foundation for developing effective combination therapies using daptomycin and glycopeptides against resistant E. faecium.