Rapid detection of carbapenemases directly from positive blood cultures by the β-CARBA test
The rapid detection of blood stream infections (BSI) by carbapenemase-producing Enterobacterales (CPE) is indispensable to early optimize antibiotic treatment and to improve survival. While phenotypic tests are time-consuming and PCR is expensive and not available in many routine laboratories, colorimetric tests (e.g., Carba NP test) can provide rapid results at moderate cost. However, up to now, the detection of CPE-BSI requires a further 3-h incubation in broth supplemented with zinc sulfate and imipenem after a blood culture has become positive, thereby causing delay and additional hands-on time. The purpose of this study was to develop and evaluate a new method for the detection of CPE directly from positive blood culture without the need for incubation in broth, based on the commercially available colorimetric β-CARBA test. For the evaluation, blood cultures spiked with 140 different Enterobacterales isolates producing diverse beta-lactamases were tested with the new method. Of these, 70 were CPE (OXA-48-like, NDM, KPC, VIM, and GIM). After blood cultures turned positive, blood culture fluid was drawn, and erythrocytes were hemolyzed with SDS, washed, and equilibrated before the β-CARBA was performed on the bacterial pellet. All carbapenemases were reliably detected, including weak carbapenemases of the OXA-48 group. The sensitivity was 100% (95% CI 94.9–100) and the specificity 94.3% (95% CI 89.2–99.4). The time to result was 20 to 45 min. Carbapenemases can rapidly and reliably be detected directly from blood cultures using the new method, which could help to improve the outcome of these difficult-to-treat infections.
KeywordsCarbapenemase Carba NP Blood stream infection NDM OXA-48
We thank Stephan Göttig from the University Hospital of Frankfurt for providing carbapenemase-producing isolates.
This study was supported by grants from the Faculty of Medicine, University Hospital of Cologne.
Compliance with ethical standards
Conflict of interest
AH reports grants from German Center for Infection Research and personal fees from Becton Dickinson, Bruker Daltonics, MSD/Merck, Astellas, Gilead, and Oxoid, outside the submitted work.
MM has no conflict of interest to report.
All procedures performed in this study were in accordance with the ethical standards of the institutional and national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
The study was approved by the ethics committee of the University Hospital Cologne (approval number 08-160) and written informed consent was obtained from all healthy volunteers who donated blood for this study.
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