CHROMagar™ VRE

For Detection of VanA/VanB Vancomycin-Resistant Enterococcus faecalis and Enterococcus faecium

CHROMagar™ VRE is a selective chromogenic culture medium designed for the detection and differentiation of vancomycin-resistant enterococci (VRE), specifically those harboring VanA and VanB resistance genes in E. faecalis and E. faecium. On this medium, VRE colonies appear pink to mauve, while intrinsically resistant Enterococcus species (e.g., E. gallinarum, E. casseliflavus) appear blue or are inhibited, allowing for precise identification of transmissible resistance.

This medium supports early screening, infection control, and outbreak surveillance in healthcare settings, while minimizing false positives associated with conventional media such as bile esculin agar.

Colony Appearance

Performance

Vancomycin resistance in enterococci is classified as:

• Intrinsic resistance (VanC, VanD, VanE, etc.) found in E. gallinarum, E. casseliflavus – low-level, non-transmissible.
• Acquired resistance (VanA, VanB) in E. faecalis, E. faecium – transmissible and clinically significant.

VanA/VanB genes pose a critical threat due to their horizontal gene transfer potential, including to pathogens like Staphylococcus aureus. Early identification of carriers is essential to limit transmission and implement targeted infection control protocols.

CDC Guidelines: “Knowledge of the type of resistance is critical for infection control purposes. VanA and VanB genes are transferable and have been associated with outbreaks.”

Intended Use

CHROMagar™ VRE is intended for:

• Qualitative detection of gastrointestinal colonization by VanA/VanB VRE (E. faecalis and E. faecium)
• Screening of rectal swabs and stool samples in hospitals and long-term care settings
• Use in epidemic outbreak response, routine VRE surveillance, or admission screening

Not intended to diagnose infection or guide treatment. Suspect colonies should undergo confirmatory testing (e.g., PCR, MALDI-TOF, susceptibility testing).

Advantages

1. High Specificity for VRE with VanA/VanB
   Accurately detects transmissible resistance types while excluding false positives from VanC-type enterococci.
2. Easy Visual Interpretation
   Distinct pink to mauve colonies for VRE E. faecalis/faecium, with non-VRE enterococci appearing blue or inhibited, simplifying plate reading.
3. Minimizes False Positives
   Unlike bile esculin-based media, CHROMagar™ VRE:
   • Differentiates E. faecium and E. faecalis
   • Avoids misleading black coloration
   • Inhibits esculin-hydrolyzing non-enterococci like Pediococcus, Leuconostoc, or Lactococcus
4. Fast Results
   Results interpretable after 24 hours of aerobic incubation at 35–37 °C.
5. Flexible Shelf Life
   Long shelf-life (>18 months) makes it ideal for:
   • Ongoing surveillance programs
   • High-volume patient screening during outbreaks

Test Procedure

1. Sample Type: Rectal swab or stool
2. Inoculation: Direct streaking onto CHROMagar™ VRE
3. Incubation:
   • Temperature: 35–37 °C
   • Time: 24 hours
   • Atmosphere: Aerobic
4. Interpretation:
   • Pink/mauve colonies = presumptive VanA/VanB VRE
   • Blue or no growth = likely VanC-type or non-enterococci

Ordering Information

Each pack includes:

• Base medium
• Supplement (VR952(S) or VR953-150(S))

Storage & Shelf Life

• Storage: 2–8 °C (sealed, dry)
• Shelf Life: Up to 24 months from date of manufacture
• Prepared Media: Use within validated expiry date per instructions

Scientific Publications

• Boschert et al., 2023 – Comparison of five selective agars for detecting VRE E. faecium
• Lüthje et al., 2023 – MALDI-TOF MS identification of colonies from chromogenic media
• Fyodorova et al., 2018 – Detection of VRE using chromogenic media (Russia)

CHROMagar™ VRE is a highly selective and reliable tool for the detection of VanA/VanB-mediated VRE colonization, supporting infection control in hospitals, ICUs, and long-term care facilities. Its distinct colony morphology, short incubation, and reduction in false positives make it the preferred choice for high-throughput VRE surveillance and outbreak containment.