Rapid On-Site Detection of Viable Escherichia Coli O157: H7 in Lettuce Using Immunomagnetic Separation Combined with PMAxx-LAMP and Nucleic Acid Lateral Flow Strip

Escherichia coli (E. coli) O157: H7 is one of the most common foodborne pathogens that can be transmitted through contaminated food and water sources, posing a serious threat to food safety and public health world-wide. The rapid and accurate diagnosis of E. coli O157: H7 infection is essential for effective control and man-agement of disease epidemics originating from food and water sources. In this study, we used immunomagnetic separation (IMS) technology to magnetically enrich E. coli O157: H7, further amplify the target gene rfbE using the method combining improved propidium monoazide (PMAxx) and loop-mediated isothermal amplification (LAMP) (PMAxx-LAMP), and detect viable E. coli O157: H7 in lettuce by the nucleic acid lateral flow strip (NALFS) method. We used IMS to capture and enrich the target bacteria, effectively eliminating the interference of the food matrix and improving the detection limit in lettuce samples. PMAxx treatment eliminated the false-positive results from dead bacteria and, in combination with LAMP-NALFS, detected viable E. coli O157: H7 accurately. The IMS-PMAxx-LAMP-NALFS assay allowed us to detect viable E. coli O157: H7 at concentrations as low as 81 CFU/g in artificially contaminated lettuce samples within 2 h without any heavy and costly in-struments. Thus, this assay provides a simple, rapid, and low-cost tool for the on-site detection of pathogenic bacteria, especially with limited resources.