A multicenter evaluation of a novel microfluidic rapid AST assay for Gram-negative bloodstream infections

Abstract

ObjectivesCommon phenotypic methods for antibiotic susceptibility testing (AST) of bacteria are slow, labour intensive and displays considerable technical variability. The QuickMIC system provides rapid AST using a microfluidic linear gradient. Here we evaluate the performance of QuickMIC at four different laboratories with regards to speed, precision, accuracy, and reproducibility in comparison to broth microdilution (BMD).MethodsSpiked blood cultures (n=411) and clinical blood cultures (n=148) were tested with the QuickMIC Gram negative (GN) panel and compared with BMD for the 12 on-panel antibiotics, and 10 defined strains were run at each site to measure reproducibility. Logistic and linear regression analysis was applied to explore factors affecting assay performance.ResultsThe overall essential agreement (EA) and categorical agreement (CA) between QuickMIC and BMD were 95.6% and 96.0%, respectively. Very major error (VME), Major error (ME) and minor error (mE) rates were 1.0, 0.6 and 2.4%, respectively. Inter-laboratory reproducibility between the sites was high at 98.9% using the acceptable standard of ±1 log2 unit. The mean in-instrument analysis time overall was 3h 13 min (SD: 29 min). Regression analysis indicated that QuickMIC is robust with regards to initial inoculate and delay time after blood culture positivity.ConclusionsWe conclude that QuickMIC can be used to rapidly measure MIC directly from blood cultures in clinical settings, with a high reproducibility, precision, and accuracy. The microfluidics-generated linear gradient ensures high repeatability and reproducibility between laboratories, thus allowing a high level of trust in MIC values from single testing, at the cost of reduced measurement range compared to BMD.