Rapid Fluorescence Concentration Immunoassay for Detection of Salmonellae in Chicken Skin Rinse Water

Salmonellae in chicken carcass rinse water or enrichment broth were detected with a fluorescence concentration immunoassay (FCIA) using intact salmonellae cells as the reacting particles. Sample Solutions and reagents were added to a 96-well fluoricon assay plate and incubated 30 min in the chamber of a fluorescence concentration analyzer at room temperature. The bound and free components were separated by automated vacuum filtration and washings through the membrane filters equipped at the bases of the wells. The fluorescent signals were concentrated through vacuum filtration and were read at a wavelength of 485/535 nm. A cut-off value of the arbitrary fluorescence units was calculated by adding two standard deviations to the mean value of the negative control. When the arbitrary fluorescence units of a sample were above the cut-off value, it was scored positive indicating the presence of salmonellae in the test suspensions. It was found the FCIA method could detect salmonellae at 1.25 × 10⁴ cells per mi in pure culture and was specific enough to screen salmonellae from four types of common chicken carcass contaminating bacteria. By coupling with 18-h direct enrichment in selenite cystine broth of the whole carcass rinse, the detection of salmonellae in chicken carcass rinse water was accomplished in less than 24 h.