Evaluation of QuickMIC system for rapid antimicrobial susceptibility testing of Gram-negative pathogens from positive blood cultures, including strains producing extended-spectrum β-lactamases and carbapenemases.

The accuracy and turnaround time (TAT) of the QuickMIC system (QMIC) for rapid antimicrobial susceptibility testing (AST) of Gram-negative pathogens from positive blood cultures were evaluated, in comparison with a standard-of-care workflow based on culture and AST with broth microdilution. Essential agreement (EA) and bias were evaluated according to the ISO 20776-2:2021, category agreement (CA), categorical overestimation (CO), and underestimation (CU) rates were evaluated according to the European Committee on Antimicrobial Susceptibility Testing(EUCAST) breakpoints, and major discrepancy (MD) and very major discrepancy (VMD) rates were evaluated according to the Food and Drug Administration (FDA) guidelines and breakpoints. QMIC yielded evaluable data for 103/118 blood cultures (87.3%), including Enterobacterales (N = 82), Pseudomonas aeruginosa (N = 16), and Acinetobacter baumannii complex (N = 5). Overall, 41 isolates (39.8%) were positive for extended-spectrum β-lactamases and/or carbapenemases. QMIC exhibited EA and CA values of 89.5% and 93.3%, respectively, with values <90% were reported for cefepime, meropenem, and piperacillin-tazobactam. Mean bias was -23.1%, with values >±30% observed with colistin and piperacillin-tazobactam. Overall, CO and CU were observed in 2.3% and 4.4% of cases. MD and VMD with FDA breakpoints were observed in 1.5% and 8.9% of cases, respectively. The lowest accuracy of QMIC in terms of CU was observed with cefepime, colistin, and gentamicin and in terms of VMD with ceftazidime-avibactam, meropenem, and piperacillin-tazobactam. The mean TAT for QMIC was 192 ± 18 min. QMIC demonstrated the potential for rapid AST, with a mean time to result of less than 4 hours, and an overall acceptable accuracy, except with some β-lactams. Further studies are warranted to assess the potential impact of QMIC implementation on clinical outcomes.IMPORTANCEThe introduction of rapid antimicrobial susceptibility testing (AST) systems for positive blood cultures (BCs) is one of the most promising technological advancements to improve bloodstream infections diagnosis, by providing faster results useful for antimicrobial stewardship. The value of such systems is expected to be higher in settings of high endemicity of antimicrobial resistance, where phenotype prediction is more difficult, and rates of inaccurate empirical therapies are expected to be higher. In this study, we investigated the accuracy and turnaround time (TAT) of a new rapid AST system for positive BCs, in comparison with a standard-of-care workflow based on broth microdilution, including several cases positive for extended-spectrum β-lactamase- and/or carbapenemase-producing Gram negatives. TAT was 192 ± 18 min, and a good accuracy was observed for testing some agents (amikacin, gentamicin, ciprofloxacin, colistin, and ceftazidime-avibactam) but a lower accuracy for testing other agents (cefepime, meropenem, and piperacillin-tazobactam). Further assessment of this technology, after improving accuracy, is warranted to evaluate the clinical impact.