Solid Medium Droplet Microarray for Miniaturized Antimicrobial Susceptibility Test

Antimicrobial susceptibility testing (AST) that is easily adaptable for point-of-care (POC) use is essential for addressing the growing threat of antibiotic resistance. Here, the solid medium droplet microarray (SM-DMA), a simple yet versatile testing platform consisting of a single microscope slide patterned with an array of 80 agar droplets (6-8  μL each), containing customizable combinations of clinically relevant antibiotics, is introduced. The test allows for easy manual sample application and features a colorimetric self-check readout. Using E. coli (DSM498) as a model organism, accurate determination of minimum inhibitory concentrations for clinically relevant antibiotics (cefotaxime, ciprofloxacin, and ampicillin), producing results consistent with EUCAST clinical breakpoints, is demonstrated. Furthermore, SM-DMA facilitates combinatorial antibiotic testing, represented by intuitive viability heatmaps. The platform is more time efficient (≈16-18 h total) compared to the conventional agar plate-based methods. Owing to the robustness, ease of use, and independence from specialized equipment, the SM-DMA can be adapted for POC applications by nontrained personnel or even by patients themselves.