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Rapid characterization schemes for surveillance isolates of vancomycin-resistant enterococci
1Department of Pathology, Washington University School of Medicine, St. Louis, Missouri 63110, USA. dsahm@thetsn.com
Journal of Clinical Microbiology
|August 1, 1997
Summary
Efficient methods for identifying vancomycin-resistant enterococci (VRE) in surveillance cultures are crucial. This study presents rapid, reliable phenotype- and PCR-based schemes for VRE characterization within 24 hours, improving laboratory workflows.
Area of Science:
- Clinical microbiology
- Infectious diseases
- Antimicrobial resistance
Background:
- Characterizing vancomycin-resistant enterococci (VRE) surveillance isolates is labor-intensive.
- Need for efficient and reliable VRE identification schemes in clinical settings.
Purpose of the Study:
- To develop and evaluate rapid phenotype-based and PCR-based schemes for VRE detection and characterization.
- To establish efficient methods for analyzing VRE surveillance cultures within 24 hours.
Main Methods:
- Utilized bile esculin azide agar with vancomycin (BEAA) for initial screening.
- Phenotypic scheme: Gram staining, vancomycin disk diffusion, and pyrazinamidase (PYR) testing.
- PCR scheme: Direct van gene detection from BEAA plates with inclusion of control primers.
Main Results:
- Phenotypic scheme accurately identified 121 VRE isolates (E. faecium, E. gallinarum, E. casseliflavus) within 24 hours.
- Vancomycin disk diffusion distinguished VanA/VanB from VanC strains based on inhibition zone size.
- PCR scheme showed 12% false-negative results for vanA/vanB without internal controls.
Conclusions:
- Phenotype- and PCR-based schemes offer efficient VRE characterization within 24 hours of isolation.
- Phenotypic methods, particularly with PYR testing and vancomycin disk diffusion, are reliable for VRE identification.
- PCR schemes require careful validation, including internal controls, to minimize false-negative results.