PMAxx dye-assisted colorimetric dual DNAzyme-LAMP (PD-cDDLAMP) for rapid phenotypic antimicrobial susceptibility testing of

Rapid antimicrobial susceptibility testing (AST) is crucial for combating antimicrobial resistance and guiding effective therapy. Conventional phenotypic AST methods are often time-consuming, requiring 18-72 h for results, while genotypic approaches often depend on pre-existing knowledge of resistance markers. Although nucleic acid-based phenotypic AST methods have reduced turnaround time, attempts to shorten antibiotic exposure often produce only small differences between susceptible and resistant bacteria. Consequently, most loop-mediated isothermal amplification (LAMP)-based phenotypic AST assays still require prolonged antibiotic exposure (up to 4 h) or rely on sophisticated high-resolution nucleic acid detection, such as digital LAMP, to accurately detect these subtle changes, limiting their simplicity. Therefore, there is a critical need to develop a rapid assay with both short antibiotic exposure times and a simple readout. To address this unmet need, we developed PMAxx dye-assisted colorimetric Dual DNAzyme-LAMP (PD-cDDLAMP), a rapid nucleic acid-based phenotypic AST method that enhances suppression of nucleic acid amplification from antibiotic-susceptible bacteria through the selective binding of photoreactive DNA-crosslinker dye (PMAxx) to the DNA of membrane-compromised cells. This strategy enables reliable discrimination between antibiotic-resistant bacteria ("signal-on") and antibiotic-susceptible bacteria ("signal-off") after only 30 min of antibiotic exposure using a user-friendly colorimetric DNAzyme-LAMP readout system. PD-cDDLAMP achieved 91.7% sensitivity, 83.3% specificity, and 87.5% accuracy in detecting IMPORTANCE: Rapid, reliable antimicrobial susceptibility testing (AST) is essential for guiding targeted therapy and combating the escalating threat of antimicrobial resistance (AMR). However, current phenotypic ASTs are too slow for urgent decision-making, and genotypic assays cannot fully capture emerging or unknown resistance mechanisms. The PMAxx dye-assisted colorimetric dual DNAzyme-loop-mediated isothermal amplification (PD-cDDLAMP) assay introduced in this work provides a rapid nucleic acid-based phenotypic AST capable of distinguishing antibiotic-resistant from susceptible bacteria within 30 min of antibiotic exposure. By combining PMAxx-mediated suppression of nucleic acid amplification in susceptible cells with equipment-free colorimetric DNAzyme-LAMP readout, PD-cDDLAMP bridges the gap between speed and phenotypic accuracy. Its high diagnostic performance, compatibility with complex matrices such as milk, and minimal instrumentation requirements position this method as a promising point-of-care tool for clinical microbiology laboratories and on-site testing environments. PD-cDDLAMP has the potential to significantly shorten time-to-result while maintaining reliability, thereby supporting antimicrobial stewardship.