Detection of Salmonella Enteritidis in shell egg contents by immunomagnetic capture and time-resolved fluorescence.

摘要

A sandwich method was developed for the detection of Salmonella in shell egg contents. Different outbreak strains of Salmonella were used to inoculate shell egg contents at levels between 1 and 25 cfu/egg. Spiked eggs were then mixed with proper enrichment media before incubation at 37C for 4-20 h. After enrichment, the bacteria were first captured by the use of immunomagnetic beads (IMBs) coated with anti-Salmonella antibodies. The captured bacteria were further labeled with samarium (Sm)-conjugated anti-Salmonella antibodies. Sandwiched Salmonella were then treated with fluorescence enhancement solution that contained strong Sm chelators. The processes ranging from IMB capture to Sm chelation were performed using an automated KingFisher apparatus (Thermo Fisher Scientific, Inc., Waltham, MA). The fluorescence intensity of chelated Sm was then measured by time-resolved fluorescence (TRF). Using this approach, the presence of ~1 cfu of outbreak strains of Salmonella Enteritidis per egg (~50 g of egg content) could be detected after enrichment for 20 h at 37C. For higher levels of S. Enteritidis contamination, e.g., 10 cfu/50 g of egg content, the enrichment time could be reduced to 5 h at 37C. Thus, depending on desired sensitivity, the whole detection process could be completed within either an 8-h shift or 24 h. The results demonstrated that a combination of IMB capture and TRF measurement could be a rapid and sensitive method for S. Enteritidis detection in eggs..