Lanthanide-labeled fluorescent-nanoparticle immunochromatographic strips enable rapid and quantitative detection of Escherichia coli O157:H7 in food samples

Abstract

A simple, rapid, highly sensitive, and quantitative fluorescence-based immunochromatographic test (ICT) was successfully developed for the determination of Escherichia coli O157:H7 in food samples. Europium (III) chelated nanoparticles (EuNPs) conjugated to monoclonal antibodies specific to the O-specific polysaccharide fractions of E. coli O157:H7 were used as the fluorescence reporter. The fluorescence was visually observable within 15 min under dark conditions with an ultraviolet light source, and a test-strip reader was used for quantitative analysis. Under optimal conditions, the visual limit of detection (LOD) of the strip was 104 CFU/mL, and the LOD for quantitative detection was as low as 5 × 102 CFU/mL with the test-strip reader. No cross-reaction was observed in six E. coli strains with different somatic (O) antigens and five other major foodborne pathogenic strains, thus indicating the good specificity of this method. Additionally, the detection sensitivity of E. coli O157:H7 was improved to 1 CFU/mL of the original bacterial content by pre-incubation for 8 h in meat (beef, pork, and chicken) and 6 h in milk samples. The average recovery of E. coli O157:H7 spiked in pork was 84.5–103%, thus indicating the accuracy and reliability of the novel test strips. The developed EuNP-ICT strip assay is highly sensitive, specific, and replicable. This detection system provides a tool that can potentially be used to detect E. coli O157:H7 and other pathogenic bacteria in food samples.