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.