Gradient-Based Microfluidic Platform for One Single Rapid Antimicrobial Susceptibility Testing.

Antimicrobial resistance is a growing problem, necessitating rapid antimicrobial susceptibility testing (AST) to enable effective in-clinic diagnostic testing and treatment. Conventional AST using broth microdilution or the Kirby-Bauer disk diffusion are time-consuming (e.g., 24-72 h), labor-intensive, and costly and consume reagents. Here, we propose a novel gradient-based microchamber microfluidic (GM) platform to perform AST assay for a wide range of antibiotic concentrations plus zero (positive control) and maximum (negative control) concentrations all in a single test. Antibiotic lateral diffusion within enriched to depleted ( and zero, respectively) cocurrent flowing fluids, moving alongside a micron-sized main channel, is led to form an antibiotic concentration profile in microchambers, connected to the depleted side of the main channel. We examined the tunability of the GM platform, in terms of producing a wide range of antibiotic concentrations in a gradient mode between two consecutive microchambers with changing either the loading fluids' flow rates or their initial concentrations. We also tested the GM platform for profiling bacteria associated with human Crohn's disease and bovine mastitis. Time to result for performing a complete AST assay was ∼ 3-4 h in the GM platform. Lastly, the GM platform tracked the bacterial growth independent of an antibiotic mechanism of action or bacterial species in a robust and easy-to-implement fashion.