One-step immunochromatographic assay for the detection of Staphylococcus aureus

An analytical system of immunochromatographic assay based on gold nanoparticles was developed to detect Staphylococcus aureus. The assay was in the sandwich format, using anti-protein A IgG with two distinct specificities. One anti-protein A IgG was immobilized in a defined detection zone on a porous nitrocellulose membrane, while the other anti-protein A IgG was conjugated with gold nanoparticles. The mixture was then passed along the porous membrane by capillary action past the anti-protein A IgG in the detection zone, binding the particles to which surface protein A was already bound to their surface, yielding a red color. The sensitivity and specificity in the immunochromatographic test were 100 and 93.0–100% for 28 S. aureus strains and 23 non-S. aureus strains, respectively. S. aureus was detected by immunochromatographic testing of two samples of precooked foods naturally contaminated with the bacterium. Eleven processed foods artificially inoculated with S. aureus at <25 CFU/g, all yielded positive results in the immunochromatographic test