Sandwich−Based Immunosensor for Electrochemical and Fluorescent Detection of F17-Positive Escherichia Coli and its F17A Fimbrial Protein

F17A protein, the major subunit of F17 fimbriae, is one of the most prevalent and crucial virulence factors among the pathogenic Escherichia coli ( E. coli ) isolated from diarrheic and septicemic animals of various species. Purification and detection of this protein is regarded as an interesting field of investigation due to its important role as a therapeutic target, such as vaccines, and as a diagnostic tool. In this context, polyclonal rabbit antibodies recognizing F17A protein were developed and validated by indirect enzyme-linked immunosorbent assay and Western blot. Moreover, sandwich biosensor using anti−F17A/gold nanoparticles conjugate as capture probe and anti−F17A antibody labelled with horseradish peroxidase (HRP) as signal amplification probe was developed for electrochemical and fluorescent detection of purified F17A protein and live E. coli bacteria positive for F17. Good specificity and sensitivity for detection of E. coli strains positive for F17 were obtained with a lower detection limit of 37 CFU/mL.