Submitted to: Journal of Rapid Methods and Automation in Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/30/2007
Publication Date: 3/3/2007
Citation: Tu, S., Gehring, A.G., Paoli, G. 2007. Detection of salmonella in liquid eggs by immunomagnetic capture and time-resolved fluorescence. Journal of Rapid Methods and Automation in Microbiology. 15:107-119 Interpretive Summary: The U.S. Department of Agriculture has estimated that per capita consumption of eggs in America will be approximately 260 in the year 2006. According to the Center for Disease Control and Prevention, however, consumption of Salmonella Enteritidis (SE) contaminated raw or undercooked eggs has led to about 118,000 cases of illness yearly. This health concern has prompted the needs of developing fast, specific, and sensitive methods to detect the presence of SE in eggs. Conventional selective enrichment and serological tests of Salmonella, including SE from eggs take 5-7 days and are labor intensive. In this research, we developed an immunomagnetic bead technique to capture SE. Captured SEs were further labeled by specific antibodies that contained unique tags. The captured SEs were then detected by a very sensitive time-resolved fluorescence (TRF) method. Using this approach, we demonstrated that the presence of 1 CFU per 5 gm of liquid egg could be detected within 6 h. The information is valuable for regulatory agencies and food safety laboratories to develop practical, automated and bead-based methodologies to detect SE in eggs.
Technical Abstract: A sandwiched method was developed for the detection of Salmonella in liquid eggs. Different out-break strains of Salmonella were used to inoculate liquid eggs at levels between 1 to 25 CFU/egg. Spiked eggs were then mixed with proper enrichment media before incubated at 37 C for 4 to 20 h. After enrichment, the bacteria were first captured by the use of immunomagnetic beads (IMB) coated with anti Salmonella antibodies. The captured bacteria were then further labeled with samarium (Sm) conjugated anti Salmonella antibodies. Sandwiched Salmonella were then treated with fluorescence enhancement solution that contained strong Sm chelator. The processes ranging from IMB capture to Sm chelation were performed using an automated KingFisher apparatus. The fluorescence intensity of chelated Sm was then measured by time-resolved fluorescence (TRF) for Sm. Using this approach, the presence of ~ 1 CFU of Salmonella per egg (~50 g of liquid eggs) could be detected after enrichment for 20 h at 37 C. For higher levels of Salmonella contamination, e.g., 10 CFU per 50 g of liquid eggs, the enrichment time could be reduced to 5 h at 37 C. The results demonstrated that a combination of IMB capture and TRF measurement could be a rapid and sensitive method for Salmonella detection in liquid eggs.