Adaptation and validation of a quantitative vanA/vanB DNA screening assay on a high-throughput PCR system

Vancomycin resistant enterococci (VRE) are a leading cause of ICU-acquired bloodstream infections in Europe. The bacterial load in enteral colonization may be associated with a higher probability of transmission. Here, we aimed to establish a quantitative vanA/vanB DNA real-time PCR assay on a high-throughput system. Limits of detection (LOD), linear range and precision were determined using serial bacterial dilutions. LOD was 46.9 digital copies (dcp)/ml for vanA and 60.8 dcp/ml for vanB . The assay showed excellent linearity between 4.7 × 10 1 and 3.5 × 10 5 dcp/ml ( vanA ) and 6.7 × 10 2 and 6.7 × 10 5 dcp/ml ( vanB ). Sensitivity was 100% for vanA and vanB , with high positive predictive value (PPV) for vanA (100%), but lower PPV for vanB (34.6%) likely due to the presence of vanB DNA positive anerobic bacteria in rectal swabs. Using the assay on enriched VRE broth vanB PPV increased to 87.2%. Quantification revealed median 2.0 × 10 4 dcp/ml in PCR positive but VRE culture negative samples and median 9.1 × 10 4 dcp/ml in VRE culture positive patients (maximum: 10 7 dcp/ml). The automated vanA/B _UTC assay can be used for vanA/vanB detection and quantification in different diagnostic settings and may support future clinical studies assessing the impact of bacterial load on risk of infection and transmission.