Abstract:

Objectives: To develop a fluorescent microsphere immunochromatographic strip test for rapid and sensitive
detection of Escherichia coli O157:H7. Methods: Carboxyl-modified fluorescent microspheres were covalently coupled
with murine anti-E coli O157:H7 monoclonal antibody, and rabbit anti-E.coli O157:H7 polyclonal antibody and donkey
anti-mouse IgG were sprayed onto the nitrocellulose membrane as the test line and control line, respectively. The
fluorescent microsphere immunochromatographic strip for the detection of E.coli O157:H7 based on double antibody
sandwich ELISA (DAS-ELISA) was developed. Results: The coupling buffer used was 0.02 mol/L PB (pH 5.0). The
monoclonal antibody/microsphere ratio was 100 μg/mg. The procedure required only 5 min for detecting samples with the
test strip. The limit of naked eye detection was as low as 1.2 × 104 CFU/mL and could be increased to 6.1 × 103 CFU/mL
by the use of a fluorescence reader. No cross-reactivity with 30 laboratory strains was found despite marginal cross-reactivity
with Staphylococcus aureus. Conclusions: For E.coli O157:H7 detection, the fluorescent microsphere strip, which provided a
novel method, has the characteristics of user-friendly operation, rapidity, high sensitivity and ease of quantification.

Key words: Escherichia coli O157:H7, fluorescent microsphere, immunochromatography, strip