Unique performance of ChromoAgar^TM VRE blue plate as a rapid VRE screening tool: Performance of ChromoAgar^TM VRE blue

Abstract

Vancomycin-resistant enterococci (VRE) are drug-resistant bacteria critical for infection control in clinical settings. This study evaluated the performance of the ChromoAgar^TM VRE blue plate (CH-blue), a novel rapid VRE screening tool, compared to the BD BBL^TM VRE selective plate (BD-VRE). The evaluation included enterococcal strains carrying vanA and vanB genes (7 strains), plasmid resistance gene-free strains (11 strains), and clinical stool samples (98 samples). The study also investigated CH-blue’s inhibitory capacity over time post-manufacture, using seven plasmid resistance gene-free strains capable of growing on CH-blue. CH-blue showed robust growth and superior visibility for vanA and vanB strains with VCM concentrations ≥ 16 μg/mL after 24 hours compared to BD-VRE. The stealthy vanB-type VRE with VCM ≤ 8 μg/mL was detected at lower bacterial concentrations on BD-VRE, while CH-blue required higher concentrations. Prolonged incubation of CH-blue beyond 48 hours reduced its inhibitory performance against some plasmid resistance gene-free strains, which further declined as its expiration date approached. These findings indicate that CH-blue is effective for rapid VRE detection within 24 hours but less sensitivity for stealthy vanB-type VRE. The selectivity of CH-blue for plasmid resistance gene-free strains decreased with prolonged incubation and approaching expiration date. BD-VRE offers higher sensitivity and selectivity in these cases. Therefore, selecting the appropriate plate requires understanding their characteristics and considering evaluation timelines and facility conditions.