Detection of Salmonella Enteriditis from Egg Components Using Different Immunomagnetic Beads and Time-resolved Fluoresce
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Detection of Salmonella Enteriditis from Egg Components Using Different Immunomagnetic Beads and Time-resolved Fluorescence Shu-I Tu & Sue A. Reed & Andrew G. Gehring & Yiping He
Received: 26 December 2007 / Accepted: 16 April 2008 / Published online: 25 June 2008 # Springer Science + Business Media, LLC 2008
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, Schiffbase bonds and unspecified proprietary chemistry were used to capture S. Enteriditis. Europium-labeled antiSalmonella antibodies completed the sandwich, and timeresolved 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
S.-I. Tu (*) : S. A. Reed : A. G. Gehring : Y. He Eastern Regional Research Center, Agricultural Research Service, United States Department of Agriculture, 600 East Mermaid Lane, Wyndmoor, PA 19038, USA e-mail: [email protected]
of the antigenic groups recognized by the antibodies on IMBs was reduced in the presence of egg yolk. Keywords Salmonella Enteriditis . Immunomagnetic Beads . Time-resolved Fluorescence . Food Safety . Egg Components
Introduction Incidents of Salmonella enterica ssp. enterica serovar Enteriditis (S. Enteriditis) infection appeared in the 1980s in the northeastern USA. It remained confined to that region through the early 1990s. As the number of infections in the northeast began to decline, the pathogen emerged on the west coast (Centers for Disease Control 2003). Even though it has now spread nationwide, infections caused by S. Enteriditis have leveled off since peaks in the mid-1990s. However, it is still the second most common serotype causing human salmonellosis (Egg Safety Center 2007). The most common sources of S. Enteriditis infections are from undercooked and raw eggs (Centers for Disease Control 2003). Salmonella Enteriditis is a concern because it can be passed from the hen to the egg prior to shell formatio
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