Rapid Detection of Outbreak Escherichia Coli 0157 and Salmonella in Alfalfa Sprouts by Immunomagnetic Capture and Time

Rapid Detection of Outbreak Escherichia Coli 0157 and Salmonella in Alfalfa Sprouts by Immunomagnetic Capture and Time-Resolved Flourescence

Authors Tu, Shu-I; Fett, William; Gehring, Andrew; Irwin, Peter

Submitted to: Meeting Abstract
Publication Acceptance Date: August 28, 2003
Publication Date: October 28, 2003

Technical Abstract: Commercially available alfalfa seeds were inoculated with low levels (- 4 CFU/g) of pathogenic bacteria. The inoculated seeds were then allowed to sprout in sterile tap water at 22 degrees C. After 48 hours, the irrigation water and sprouts were separately transferred to bovine hear infusion (BHI) media. The microbes in the BHI samples were allowed to grow for 4 hours at 37 degrees C and 160 rpm. Specific immunomagnetic beads (IMB) were then applied to capture the E. coli 0157 and/or Salmonella in the growth media. Separation and concentration of IMB-captured pathogens were achieved using magnetic separators. The captured E. coli 0157:H7 and Salmonella spp were further tagged with europium (Eu) labeled anti-E. coli 0157 antibodies and samarium (Sm) labeled anti-Salmonella antibodies, respectively. After washing, the lanthanide labels were extracted out from the complexes by specific chelators to form strongly fluorescent chelates. The specific time-resolved fluorescence (TRF) associated with Eu or Sm was measured to estimate the extent of capture of the E. coli 0157 and Salmonella, respectively. The results indicated that the approach could detect E. coli 0157 and Salmonella enterica from the seeds inoculated with - 4 CFU/g of the pathogens. Non-targeted bacteria, e.g., Aeromonas and Citrobacter exhibited essentially no cross reactivity. Since the pathogen detection from the sprouts was achieved within 6 hours, the developed methodology could be used as a raid sensitive and specific screening process for E. coli 0157 and Salmonella enterica in this popular salad food.