Evaluation of the automated BD Phoenix CPO Detect panel in combination with the β-CARBA assay for detection and classification of carbapenemase-producing Enterobacterales

Recently, the CPO Detect panel for the detection of carbapenemase-producing, Gram-negative bacteria was introduced for the Phoenix semi-automated antimicrobial susceptibility testing system. The CPO Detect assay aims to detect carbapenemase activity (P/N test) and to type carbapenemase producers according to the Ambler classification (Ambler test). The P/N test-based detection of carbapenemase producers was 100% sensitive and 55.3% specific in the assessment of 57 carbapenemase-producing and 38 non-carbapenemase-producing Enterobacterales. False-positive test isolates in the P/N test arose from carbapenemase-non-producing, but carbapenem-non-susceptible isolates. In contrast, using the Ambler test-based approach for carbapenemase detection resulted in a specificity of 100% and a sensitivity of 79%. In order to improve the overall performance, we established an algorithm that additionally included the colorimetric β-CARBA assay as downstream test for P/N test-positive isolates, which remained un-typed in the Ambler test. This algorithm displayed an overall sensitivity and specificity of 98.3% and 100%, respectively. Our data demonstrate that the combination of the CPO Detect assay with the β-CARBA test allows for rapid detection and classification of carbapenemase-producing Enterobacterales. •The BD CPO Detect panel is an automated test for detection of carbapenemases.•It detects carbapenemases and additionally provides their Ambler classification.•We tested 57 and 38 Enterobacterales with and without carbapenemase production.•The overall sensitivity and specificity were 100% and 55.3%, respectively.•Applying the β-CARBA assay as downstream test significantly improved specificity.