V. HINIC¹, I. AMREIN², D. MEINEL¹, R. FREI¹, A. EGLI<sup>1

1</sup>Division of Clinical Microbiology, University Hospital Basel, Basel, Switzerland, ²Bioanalytica AG, Lucerne, Switzerland

Objectives: We compared the performance of two commercially available biochemical screening tests and two chromogenic selective media for detection of carbapenemase-producing Gram-negative bacteria.


Materials and methods: RAPIDEC® CARBA NP (bioMérieux) was performed according to the recently published updated protocol (JCM 2015,53:12) and Neo-Rapid CARB test (Rosco Diagnostica) according to the manufacturer’s protocol. The biplates chromID® CARBA SMART (CARB/OXA; bioMérieux) and BrillanceTM CRE/ESBL (Thermo Scientific) were streaked with 1 µl of 104 CFU/ml bacterial suspensions. Carbapenemase-positive strains not growing on chromID® CARBA SMART were additionally inoculated onto chromID® ESBL (bioMérieux). 54 well characterized carbapenemase-producing clinical isolates were tested: 35 Enterobacteriaceae (8 KPC, 1 IMI, 8 NDM, 7 VIM, 9 OXA-48-like and 2 OXA-48-like/NDM), 10 Pseudomonas aeruginosa (6 VIM, 3 IMP and 1 SPM) and 9 Acinetobacter baumannii (5 OXA-23, 3 OXA-40 and 1 OXA-23/NDM). Additionally, 46 carbapenemase-negative strains were analyzed including 12 ESBL, 17 AmpC and 1 K1. To ensure objective reading and interpretation, all strains were coded and tested blindly.


Results: The overall sensitivity of RAPIDEC® CARBA NP and Neo-Rapid CARB test was 87.0% (47/54) and 72.2% (39/54), respectively. Sensitivity calculated without A. baumannii strains was 95.5% (43/45) for RAPIDEC® and 86.7% (39/45) for Neo-Rapid CARB. Specificity for both tests was 100%. The sensitivity of chromID® CARBA SMART biplate was 90.7% (49/54), but when chromID® ESBL plate was added, the sensitivity increased to 100%. Sensitivity of the CRE part of BrillanceTM biplate was 75.9% (41/54), but together with the ESBL part 98.1% (53/54).


Conclusions: Although sensitivity of RAPIDEC® CARBA NP was significantly better than of Neo-Rapid CARB test, the performance with OXA-producing A. baumannii and OXA-48-like Enterobacteriaceae was not optimal in this blinded study. The highest sensitivity for carbapenemase screening could be achieved when an ESBL screening plate was added to chromID® CARBA SMART biplate and when BrillanceTM CRE was used in combination with BrillanceTM ESBL.