Quantitating staphylococcal enterotoxin B in diverse media using a portable fiber-optic biosensor.

A new, portable fiber-optic biosensor has been used to detect staphylococcal enterotoxin B, a causative agent of food poisoning, at levels as low as 0.5 ng/ml in buffer. The toxin (SEB) can also be detected and quantitated in other relevant media: human serum, urine, and aqueous extract of ham. The level of toxin, from 5 to 200 ng/ml, can be accurately predicted in these media by calibrating each fiber and by comparing results to a single standard curve based on toxin in buffer. The quantitative fluorescent sandwich immunoassay provides results in 45 min; qualitative results are provided in 15-20 min. Using a blender and a benchtop centrifuge, fast, simple aqueous extracts of contaminated ham samples were prepared and tested. Ham spiked with 5 or 40 micrograms SEB per 100 g food resulted in biosensor readings indicative of 11 or 69% recovery of the toxin, respectively. Finally, the SEB assay is highly specific; SEA and SED give only 2-3% of the signal at 5000 ng/ml as SEB gives at 1000 ng/ml. This specific, sensitive assay for SEB on the portable fiber-optic biosensor permits easy monitoring of clinical samples or on-site analysis of suspect food samples.