Rapid detection of <scp><i>Escherichia coli</i> O157</scp>:<scp>H7</scp> in milk, bread, and jelly by lac dye <scp>coloration‐based</scp> bidirectional lateral flow immunoassay strip

Abstract

Abstract Lac dye, a kind of food additive and textile dye, is extracted from lac insect secretions. The ability of lac dye to stain bacteria was firstly found. Based on the discovery, a new bidirectional lateral flow immunoassay strip (BLFIS) for detecting Escherichia coli O157:H7 ( E. coli O157:H7) was successfully developed. The BLFIS has two sheets of nitrocellulose (NC) membranes separated by a sample pad. The anti‐ E. coli O157:H7 monoclonal antibodies (McAb) were oppositely dispensed on the NC membranes as the control line and test line, respectively. On the side of the control line, a conjugation pad immobilized with pre‐stained E. coli O157:H7 was assembled. The detection limit of BLFIS was 10 6 CFU/ml. Furthermore, after pre‐incubation in food sample, the detection sensitivity was significantly increased to 100 colonies of the initial bacterial count. This method may be an improvement over traditional colloidal gold lateral flow immunoassay strips, which does not require the pairing of two antibodies to complete the detection, nor the chromogenic nanomaterials to report the detection results, such as gold nanoparticles. And the BLFIS might provide technical support for detecting E. coli O157:H7 in food and ensuring food safety.