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Susceptibility of enterococci to daptomycin is dependent upon testing methodology

Kendall A Bryant1, Amity L Roberts, Mark E Rupp

  • 1Department of Pathology and Microbiology, College of Medicine, University of Nebraska Medical Center, 984031 Nebraska Medical Center, Omaha, NE 68198-4031, USA.

Diagnostic Microbiology and Infectious Disease
|May 31, 2013
PubMed

Insights

MicroScan methods may overestimate daptomycin nonsusceptible enterococci (DNSE) prevalence. Further testing is needed to determine the most accurate method for confirming DNSE nonsusceptibility.

Area of Science:

  • Clinical Microbiology
  • Infectious Diseases
  • Antimicrobial Resistance

Background:

  • An increasing prevalence of daptomycin nonsusceptible enterococci (DNSE) was observed, potentially due to overestimation by current laboratory methods.
  • Enterococci infections are a growing concern, particularly those exhibiting resistance to critical antibiotics like daptomycin.

Purpose of the Study:

  • To evaluate the accuracy of different antimicrobial susceptibility testing (AST) methods for detecting daptomycin nonsusceptibility in enterococci.
  • To compare MicroScan (prompt and turbidity), Etest, and Sensititre methods against broth microdilution (BMD) for DNSE detection.

Main Methods:

  • 150 clinical isolates of enterococci were tested for daptomycin susceptibility using BMD, Etest, Sensititre, MicroScan prompt (MSP), and MicroScan turbidity (MST).
  • Categorical and essential agreement were assessed, along with error rates (very major, major, minor).
  • Pulsed-field gel electrophoresis (PFGE) was used to investigate potential clonal outbreaks.

Main Results:

  • Only 20% of isolates initially identified as DNSE by MicroScan were confirmed nonsusceptible by BMD.
  • MSP and MST showed high categorical agreement but missed a majority of resistant isolates (70% and 87%, respectively).
  • Etest yielded higher MICs, with a high rate of falsely nonsusceptible results (22%) and a low very major error rate (37%). Sensititre missed 57% of DNSE.

Conclusions:

  • MicroScan methods likely overestimate DNSE prevalence.
  • Significant discrepancies between AST methods highlight challenges in accurately confirming daptomycin nonsusceptibility.
  • Further research is required to establish a gold standard for DNSE susceptibility testing.
Keywords:
DaptomycinEnterococcusSusceptibility testing

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