μSTRAW: In-Field Detection of Escherichia coli

Fast detection of Escherichia coli is required in multiple OneHealth settings, from bathing water to urinary tract infections (urine) and septicemia (i.e., blood infections). Current methods for bacteria enumeration are limited to lab-based conventional microbiology, requiring 24-48 h. Nucleic acid testing represents an alternative, with high specificity and a broad range of targets. However, a scalable and affordable method for portable DNA extraction is missing, limiting point-of-care applications. To address that gap, we introduced μSTRAW, a compact gravity-driven microfluidic device for portable DNA extraction, which directly interfaces with a commercial, portable LAMP instrument. Using 45 mm-long, 10-bored 200 μm i.d. microcapillary strips and a magnetic beads (MB)-based extraction kit, MB were captured and efficiently washed before DNA elution. μSTRAW offered simultaneous detection from 8 samples, and the usage of MB, lysis buffer, and proteinase K was reduced by 91, 83, and 65% compared to the manufacturer's protocol. Integration with portable LAMP showed a low limit of detection (LLoD) in the range of 1000-5000 CFU/mL in PBS within 120-140 min, which improved to 50-100 CFU/mL using a pre-concentration with a 0.22 μm-pore-size syringe filter. μSTRAW also yielded an LLoD of 100-1000 CFU/mL in synthetic urine, whereas in sheep blood, we observed an LLoD as low as 10-23 CFU/mL upon 5 h of incubation in LB broth, which was therefore within the common CFU/mL found for bloodstream infections. The proposed approach is portable, affordable, scalable, and potentially transformative for a range of global OneHealth applications, especially bathing waters and wastewater.