Analysis of a persistent outbreak with vancomycin-resistant Enterococcus faecium revealed the need for an adapted...

Area of Science:

• Clinical microbiology
• Infectious disease diagnostics
• Molecular epidemiology

Background:

• An outbreak of vancomycin-resistant Enterococcus faecium (VREfm) occurred, involving strains with vanA and/or vanB resistance genes.
• Initial screening using vanA/vanB real-time polymerase chain reaction (PCR) detected vanB resistance with low cycle threshold values, but VREfm-specific cultures were negative.

Purpose of the Study:

• To analyze diagnostic results during a VREfm outbreak.
• To adapt the diagnostic algorithm based on performance of different VREfm detection methods.

Main Methods:

• Comparison of vanA/vanB real-time PCR results with VREfm-specific culture methods (Brilliance VRE and CHROMagar VRE).
• Genotyping of identified VREfm isolates to characterize strains.
• Evaluation of diagnostic performance during an active VREfm outbreak.

Main Results:

• Four distinct VREfm strains were identified: vanA (STnew-CT7088) and vanB (ST80-CT1065, ST117-CT7117, ST117-CT7118).
• Brilliance VRE agar culture was inadequate for detecting vanB ST117 isolates, despite varying vancomycin minimum inhibitory concentrations.
• CHROMagar VRE successfully detected all tested VREfm isolates, including the problematic vanB ST117 strains.

Conclusions:

• The inadequacy of Brilliance VRE agar for detecting vanB ST117 isolates may have contributed to unnoticed VREfm spread.
• CHROMagar VRE demonstrated superior performance and was implemented in routine diagnostics, replacing Brilliance VRE agar.