Development and validation of a lateral flow immunoassay for rapid detection of VanA-producing enterococci.

Oueslati, Saoussen; Volland, Hervé; Cattoir, Vincent; Bernabeu, Sandrine; Girlich, Delphine; Dulac, Ducan; Plaisance, Marc; Laroche, Maxime; Dortet, Laurent; Simon, Stéphanie; Naas, Thierry

BACKGROUND VRE are nosocomial pathogens with an increasing incidence in recent decades. Rapid detection is crucial to reduce their spread and prevent infections and outbreaks. OBJECTIVES To evaluate a lateral flow immunoassay (LFIA) (called NG-Test VanA) for the rapid and reliable detection of VanA-producing VRE (VanA-VRE) from colonies and broth. METHODS NG-Test VanA was validated on 135 well-characterized enterococcal isolates grown on Mueller-Hinton (MH) agar (including 40 VanA-VRE). Different agar plates and culture broths widely used in routine laboratories for culture of enterococci were tested. RESULTS All 40 VanA-VRE clinical isolates were correctly detected in less than 15 min irrespective of the species expressing the VanA ligase and the medium used for bacterial growth. No cross-reaction was observed with any other clinically relevant ligases (VanB, C1, C2, D, E, G, L, M and N). Overall, the sensitivity and specificity of the assay were 100% for VanA-VRE grown on MH agar plates. NG-Test VanA accurately detects VanA-VRE irrespective of the culture medium (agar and broth). Band intensity was increased when using bacteria grown on vancomycin-containing culture media or on MH close to the vancomycin disc as a consequence of VanA induction. The limit of detection of the assay was 6.3 × 106 cfu per test with bacteria grown on MH plates and 4.9 × 105 cfu per test with bacteria grown on ChromID® VRE plates. CONCLUSIONS NG-Test VanA is efficient, rapid and easy to implement in the routine workflow of a clinical microbiology laboratory for the confirmation of VanA-VRE.