resaCPE: A Rapid, Low-Cost Colourimetric Assay for the Detection of Carbapenemase-Producing Enterobacterales

The use of carbapenem antibiotics is threatened by the global spread of carbapenemase-producing Enterobacterales (CPE), bacterial pathogens which hydrolyze these last-resort antimicrobials. Rapid detection of CPE is vital to ensure timely administration of antimicrobial therapy to infected patients, as well as the implementation of infection control measures to prevent outbreaks in healthcare settings. In this study, we report the development of resaCPE, a rapid, low-cost CPE detection method that couples the inactivation of an imipenem disk with a cell viability assay employing a carbapenem-hyper-susceptible Escherichia coli strain. Results are interpreted by a simple colourimetric readout in which CPE-positive samples turn pink, while CPE-negative samples remain purple. The assay was validated with a panel of 91 CPE and non-CPE isolates, and its performance compared to two widely used CPE detection strategies, the modified carbapenem inactivation method (mCIM) and the CARBA-NP test. The resaCPE test demonstrated the same level of performance as the mCIM (100 % sensitivity and specificity), while providing results in significantly less time (3.5 h vs. 20-24 h, respectively). We also observed that the resaCPE test outperformed the CARBA-NP test (95.3 % sensitivity, 100 % specificity), specifically when applied to the detection of CPE isolates producing carbapenemases with weaker hydrolytic activity. Due to the rapid turnaround time, minimal setup requirements, and low cost ([~]$1 USD/sample), the resaCPE test is a potentially attractive option for primary CPE screening, particularly in lower resource settings.