Use of biotin-labeled IgY overcomes protein A interference in immunoassays involving Staphylococcus aureus antigens

Staphylococcal protein A (SpA) is an immunoglobulin-binding protein secreted by all Staphylococcus aureus strains and is responsible for high false positives during immunoassays. Avian IgY were reported to eliminate SpA interference when used as a capture antibody in a double antibody sandwich format. But this procedure requires generating two antibodies in different animals for capture and revealing antibodies. In the present study, a simple enzyme-linked immunosorbent assay (ELISA) was developed and evaluated for detection of staphylococcal enterotoxin B without any interference by SpA. Biotin-labeled IgY were used for probing for staphylococcal enterotoxin B (SEB) so that streptavidin-horseradish peroxidase (HRP) could be used for color development instead of anti-chicken IgG-HRP, which interferes in the assay by binding to SpA. Western blotting, dot ELISA, and polymerase chain reaction (PCR) were performed to validate the results of the biotin IgY ELISA to show that the assay was free from SpA interference. Large numbers of S. aureus strains were screened for SEB production. Sensitivity of the assay was similar to 10 ng/ml of SEB in spiked milk samples. The ELISA was specific to SEB, with no cross-reactivity to other closely related enterotoxins (SEA, SEC, SED, SEE). The presently described ELISA is highly effective in eliminating SpA interference and this method does not require the need for two different antibodies, as in the sandwich ELISA.