Precise digital bacteria enumeration and antibiotic susceptibility testing via a portable vibrating capillary-based droplet platform

Antibiotic resistance can lead to multidrug-resistant superbugs and threaten global health, putting forward a high demand for accurate and fast antibiotic susceptibility testing (AST). Conventional AST methods are labor-intensive and time-consuming, far from meeting the requirement for rapid clinical decision-making. Here, we develop a portable vibrating capillary-based droplet platform for precise digital bacteria enumeration and rapid AST. Multi-volume droplets encapsulating bacteria with or without antibiotics are generated on demand, and the elevated fluorescence from resazurin reduction is measured, which corresponds to the growing bacteria. Automated data analysis is achieved by a self-developed image processing program. Multi-volume droplet digital counting allows precise bacteria enumeration over a wide dynamic range spanning more than 4 orders of magnitude. Droplet digital AST of ampicillin against E. coli demonstrates that it is feasible for accurately assessing the minimum inhibitory concentration and investigating the inoculum effect, with the assay time reduced to 5 h. In sum, this method is easy to operate, cost-effective, with high accuracy and short time-to-result, which is highly promising for rapid and precise assessment of antimicrobial susceptibility in resource-limited settings.