Rapid antimicrobial susceptibility tests performed by self-diluting microfluidic chips for drug resistance studies and point-of-care diagnostics.

Antimicrobial resistance (AMR) is a global public health issue. Rapid and accurate antimicrobial susceptibility tests (AST) on bacteria isolates would facilitate appropriate choice of antibiotics, in which patients receive appropriate treatment and the emergence of multidrug-resistant organisms could be prevented simultaneously. In this study, we have developed a microfluidic device named Self Dilution for Faster Antimicrobial Susceptibility Testing (SDFAST). This SlipChip-based device consists of two layers of microchips, allowing injection of bacterial suspension and antibiotics by simply connecting the two chips. By slipping one microchip against another in a single press of the microchip, the antibiotics can be diluted within seconds and be well mixed with bacterial samples. By combining SDFAST with a water-soluble tetrazolium salt-8 (WST-8) assay, a range of clinically prevalent bacteria, including Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Staphylococci species, were tested under various antibiotics. Color analysis after 4-6 h of incubation showed an abrupt change in the WST-8 color of certain wells with diluted antibiotics, proving that instrument-free and immediate identification of minimum inhibitory concentration (MIC) could be achieved. The testing on 51 clinical isolates had an agreement of 92%, proving the accuracy of our method. These results validated its advantages of simple operation, rapid testing, and low sample consumption comparing to conventional methods, which require 16-24 h of incubation. Therefore, our method shows great potential to be further developed into a medical instrument for automated medical testing and point-of-care diagnosis.