Clinical Usefulness of the QMAC-dRAST System for AmpC β-lactamase-Producing Enterobacterales

Abstract

Background: Rapid antimicrobial susceptibility testing (RAST) is important for theappropriate treatment of bloodstream infections. The QMAC-dRAST system (QuantaMatrixInc., Korea) can directly perform RAST using positive blood culture samples with microscopicimaging. This study aimed to evaluate the performance of the QMAC-dRAST system for AmpC-β-lactamase-producing Enterobacterales. Methods: Eighty isolates (20 Morganella morganii, 20 Serratia marcescens, 10 Klebsiellaaerogenes, 10 Enterobacter cloacae, and 20 Citrobacter freundii) and 14 antimicrobial agentswere included in the antimicrobial susceptibility testing (AST). The performance of theQMAC-dRAST system was evaluated by simulating the clinical blood culturing process. Weconducted a comparative evaluation of the QMAC-dRAST and Vitek 2 systems (bioMérieux Inc.,France). Broth microdilution tests were performed as the reference method to resolve anydiscrepancies in the AST results between the two systems. Results: For 20 M. morganii and 20 S. marcescens, the categorical agreement (CA) betweenthe QMAC-dRAST and Vitek 2 systems increased from 55.4% to 83.8% after AST algorithmoptimization. Moreover, the discrepancy rates decreased as follows: from 19.1% to 5.4% verymajor errors (VME), from 38.3% to 4.3% major errors (ME), and from 14.6% to 12.1% minorerrors (mE) for the QMAC-dRAST system compared to the Vitek 2 system. For all 80 testedisolates, the QMAC-dRAST system showed 93.0% CA, 1.7% VME, 2.3% ME, and 4.9% mE. Conclusion: The QMAC-dRAST system was comparable to the Vitek 2 system after ASTalgorithm optimization for AmpC β-lactamase-producers, which are major pathogens andrequire time to express the enzyme. However, further modifications of the AST algorithm arestill warranted.