Simple sensitive rapid detection of Escherichia coli O157:H7 in food samples by label-free immunofluorescence strip sensor

A simple, one-step, rapid method to detect Escherichia coli O157: H7 (E. coli O157: H7) using a label-free immunofluorescence strip sensor is presented. Fluorescein isothiocyanate (FITC) was added to the sample culture medium to prepare the fluorescent probe for the label-free strip sensor. With the presence of E. coli O157: H7 in the samples, the bacteria could emit a yellow-green fluorescence after incubation and maintain good affinity to the monoclonal antibodies (McAb) against E. coli O157: H7. The direct-type immunofluorescence strip sensor was based on the binding between fluorescent bacteria and the unlabeled McAb immobilized at the test line in nitrocellulose membrane (NC membrane) reaction zone. The visual limit of detection (LOD) of the strip for qualitative detection was 10(6) cells/mL while the LOD for semi-quantitative detection could go down to 10(5) cells/mL by using scanning reader. The LOD was substantially improved to 1 cells/mL of the original bacterial content after pre-incubation of the bread, milk and jelly samples in broth for 10, 10 and 8 h respectively, which was competitive to some current rapid E. coli O157: H7 detection methods. Besides the obvious advantages, including reduced detection time and operation procedures, the results of this method meet the various detection requirements for E. coli O157: H7 and are comparable to the traditional enzyme-linked immunosorbent assay (ELISA) and double antibody sandwich gold-labeled strips. This is the first report of semi-quantitative immunofluorescence strip for directly detecting foodborne pathogen using only one unlabeled antibody. All detections could be achieved in less than 5 min. In addition, this simple, low-cost and easy to be popularized method served as a significant step towards the development of monitoring foodborne pathogens in food-safety testing. (C) 2016 Elsevier B.V. All rights reserved.