Defining daptomycin resistance prevention exposures in vancomycin-resistant Enterococcus faecium and E. faecalis.

Area of Science:

• Microbiology
• Pharmacology
• Infectious Diseases

Background:

• Daptomycin is used off-label for enterococcal infections, but optimal dosing for resistance prevention is unknown.
• Standard daptomycin doses (4-6 mg/kg/day) approved for staphylococci may be insufficient for enterococci due to reduced susceptibility.

Purpose of the Study:

• To model daptomycin regimens in vitro to determine the minimum drug exposure required to prevent daptomycin resistance (Dapr) in enterococci.
• To investigate the genetic and phenotypic changes associated with Dapr in enterococcal strains.

Main Methods:

• Simulated daptomycin regimens (4-12 mg/kg/day) were tested against Enterococcus faecium and Enterococcus faecalis in a 14-day pharmacokinetic/pharmacodynamic model.
• Daptomycin resistance was detected by plating on media with 3x the minimum inhibitory concentration (MIC).
• Mutations in resistance-associated genes (yycFG, liaFSR, cls, cfa) and phenotypic changes (susceptibility, surface charge, depolarization, cell wall thickness, growth rate) were analyzed.

Main Results:

• Enterococcal strains developed Dapr at simulated doses of 4-8 mg/kg/day but not at 10-12 mg/kg/day.
• Daptomycin-resistant strains showed increased MICs (8-256 mg/liter), reduced growth rates, decreased daptomycin-induced membrane depolarization, and increased cell wall thickness.
• Specific mutations were identified in some resistant strains (liaF, cls).

Conclusions:

• Daptomycin doses of 10 mg/kg/day may be necessary to prevent Dapr in serious enterococcal infections.
• Understanding the mechanisms of Dapr is essential for optimizing daptomycin therapy against enterococci.