Rapid detection of Escherichia coli O157:H7 by a fluorescent microsphere-based immunochromatographic assay and immunomagnetic separation

To ensure food safety and avoid infections by Escherichia coli O157:H7 (E. coli O157:H7), we developed a novel fluorescent microsphere (FM)-based immunochromatography assay (FM-ICA). FMs were conjugated to anti-E. coli O157:H7 monoclonal antibody (MAb) as an ICA probe, Immunomagnetic beads (IM-beads) were prepared by conjugating functionalized magnetic microspheres with the antibody for enrichment and separation of pathogenic bacteria from complex food matrices. Under selected conditions, a standard curve of FM-ICA measurement of E. coli. O157:H7 was developed with a linear range from 3 x 10(3) to 6 x 1(0)7 colony-forming units (CFU)/mL in PBS buffer. The recoveries of intra- and inter assay ranged from 101.64% to 107.03% and 95.62%-110.2% respectively, with CV below 10%. The FM-ICA showed good sensitivity, accuracy and precision. When IM-beads separation plus FM-ICA (IMS-FICA) were used to assay raw food samples, sensitivity was 3 x 10(3) CFU/mL, a 33 fold improvement compared with FM-ICA only. Moreover, this method had high specificity for E. coli O157:H7 and can be used to assay E. colt O157:H7 in beef, milk and water samples. This assay can be completed within 2 h and has great potential for on-site quantitation of E. coli O157:H7 with simplicity, rapidity, sensitivity, and cost-effectiveness.