Detection of Salmonella Enteriditis from Egg Components Using Different Immunomagnetic Beads and Time-resolved Fluorescence

Abstract

The types of chemical linkage used to bind antibodies to magnetic beads to form immunomagnetic beads (IMB) were compared in the capture and detection of Salmonella Enteriditis from egg white, egg yolk, and whole egg. Egg components were inoculated with outbreak strains of S. Enteriditis. After incubation under different conditions, IMBs derived from linking antibodies to core magnetic beads via biotin–streptavidin interactions, Schiff-base bonds and unspecified proprietary chemistry were used to capture S. Enteriditis. Europium-labeled anti-Salmonella antibodies completed the sandwich, and time-resolved fluorescence served as the means of detection. For the Salmonella isolated in stationary phase and cultured from universal pre-enrichment broth (UPB), the detection signal intensity was affected by the chemistry utilized to link the antibodies to IMB, with results varying among the three test strains. When S. Enteriditis was cultured in egg yolk alone, plating data were similar to those of the growth of S. Enteriditis in UPB. Egg white by itself did not support the growth of S. Enteriditis. The addition of UPB to egg white restored the growth of Salmonella and yielded stronger detection signals than from cultures obtained from UPB with egg yolk. The detection signals obtained from the immunoassay were less intense for cultures grown in egg yolk + UPB than from cultures grown in UPB alone. The lower detection signals elicited by all IMBs suggest the availability of the antigenic groups recognized by the antibodies on IMBs was reduced in the presence of egg yolk.