A Rapid Colorimetric LAMP Assay for Escherichia coli O157:H7 Detection in Water with Smartphone Readout

Abstract Rapid on-site detection of Escherichia coli O157:H7 is essential for immediate decision-making in water-safety monitoring. We developed and validated a portable colorimetric loop-mediated isothermal amplification (LAMP) assay targeting the rfbE gene of E. coli O157:H7, coupled with smartphone-based image acquisition and automated color-index analysis.Samples were concentrated via membrane filtration and lysed by heat (95 °C, 5 min). LAMPreactions (65°C) containing hydroxynaphthol blue (HNB) were incubated 30–45 min;endpoint and kinetic data were captured by smartphone and analyzed using an RGB-derivedhue index. Analytical limit of detection (LOD) in spiked sterile water was ~10 CFU/mL;LOD increased marginally in turbid environmental waters. No cross-reactivity was observedwith non-O157 strains. Total time-to-result from sampling to readout was <60 min. The assay meets REASSURED criteria for decentralized diagnostics (sensitive, specific, rapid, user-friendly, equipment-light, and connected) and is suitable for field deployment.