Evaluation of the speed, accuracy and precision of the QuickMIC rapid antibiotic susceptibility testing assay in a clinical setting

The rapidly changing landscape of antimicrobial resistance poses a challenge for empirical antibiotic therapy in severely ill patients and highlights the need for fast antibiotic susceptibility diagnostics to guide treatment. Traditional methods for antibiotic susceptibility testing (AST) of bacteria such as broth microdilution (BMD) or the disc diffusion method (DDM) are comparatively slow and show high variability. Rapid AST methods under development often trade speed for resolution, sometimes only measuring responses at a single antibiotic concentration. QuickMIC is a recently developed lab-on-a-chip system for rapid AST. Here we evaluate the performance of the QuickMIC method with regard to speed, precision and accuracy in comparison to traditional diagnostic methods. 151 blood cultures of clinical Gram-negative isolates with a high frequency of drug resistance were tested with the QuickMIC system and compared with BMD for 12 antibiotics. To investigate sample turnaround time and functionality in a clinical setting, another 41 clinical blood culture samples were acquired from the Uppsala University Hospital and analyzed on site in the clinical laboratory with the QuickMIC system, and compared with DDM for 8 antibiotics routinely used in the clinical laboratory. The overall essential agreement between MIC values obtained by QuickMIC and BMD was 83.2%, with an average time to result of 3 h 2 min (SD: 24.8 min) for the QuickMIC method. For the clinical dataset, the categorical agreement was 94.9%, and the total turnaround time as compared to routine diagnostics reduced by 40% (33 h vs. 55 h). Interexperiment variability was low (average SD: 44.6% from target MIC) compared to the acceptable standard of ±1 log2 unit ( i . e . -50% to +100% deviation from target MIC) in BMD. We conclude that the QuickMIC method can provide rapid and accurate AST, and may be especially valuable in settings with high resistance rates and for antibiotics where wildtype and resistant MIC distributions are close or overlapping. ### Competing Interest Statement Christer Malmberg is a part-time employee of Gradientech AB. Jessie Torpner, Jenny Fernberg, Hakan Ohrn and Cecilia Johansson are employees of Gradientech AB. Thomas Tangden declares no conflicts of interest. Johan Kreuger is not employed by Gradientech AB but is a co-founder of Gradientech AB and owns stock in the company.