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United States Department of Agriculture

Agricultural Research Service

Title: A Biosensor Method for Detection of Staphylococcal Enterotoxin a (Sea) in Raw Whole Egg

Author
item Medina, Marjorie

Submitted to: Biotechnology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 8, 2006
Publication Date: April 1, 2006
Citation: Medina, M.B. 2006. A biosensor method for detection of staphylococcal enterotoxin a (sea) in raw whole egg. Biotechnology Letters. 2006. v.14. pg.119-132.

Interpretive Summary: The foodborne pathogenic bacterium, Staphylococcus aureus, produces toxins that cause major gastroenteritis even with only a trace amount of the toxins. Common heat processing and normal cooking temperatures can kill the bacteria but do not destroy the toxins. Therefore, ingestion of toxin contaminated foods can still cause an illness. Staphylococcal enterotoxin A (SEA) is the most recovered staphylococcal enterotoxin in food poisoning outbreaks. As per a request by The Food Safety and Inspection Service (FSIS), we developed a biosensor method for the detection of SEA in liquid eggs. The method consisted of preparation of the SEA sensor surface, egg sample preparation and the biosensor analysis. SEA was added to raw eggs and the samples were clarified by centrifugation. Anti-SEA antibody was added and allowed to bind with SEA in samples and the SEA/anti-SEA complex was separated from the unbound anti-SEA by centrifugation. The sample portions containing the free anti-SEA were injected over the sensor and was then captured by SEA sensor. This biosensor method detected 1-40 ng/mL (ppb) SEA in whole eggs.The automated biosensor method completed SEA analysis at 15 min. per sample. This method provides the FSIS an alternative method to validate the results from commercial assays for SEA detection in liquid eggs. The method can also be used by the industry to monitor the presence of enterotoxins in foods.

Technical Abstract: Staphylococcus aureus produces enteric toxins that cause major foodborne gastroenteritis. Under temperature-abused conditions, the organism can grow in foods of animal origin. Heat processing and normal cooking temperatures can inactivate or kill the bacterial cells but the enterotoxins (SE) are heat stable. Staphylococcal enterotoxin A (SEA) is the most recovered staphylococal enterotoxin in food poisoning outbreaks. Our research objective is to develop a competitive immunoassay using a surface plasmon resonance (SPR) biosensor for the detection of SEA in raw egg. The method consisted of preparation of the SEA sensor surface. Raw egg was homogenized with a sonicator and aliquots were spiked with SEA. The spiked samples were centrifuged at 14,889g. Anti-SEA was added and allowed to bind with SEA in samples off-line and the SEA/anti-SEA complex was separated from the free anti-SEA by centrifugation. The supernatants were injected over the sensor and the excess unbound anti-SEA was then captured by SEA sensor. The sensor surface was regenerated with 100 mM HCl. The RU responses were plotted against spiked SEA concentration. SEA was detected in whole egg at 1-40 ng/mL (ppb). The biosensor analysis including the sensor regeneration was 15 min. per sample in a fully automated system. The competitive biosensor assay will be utilized for SEA detection in liquid eggs and for multiple toxin detection of staphylococcal toxins in foods.

Last Modified: 11/22/2014
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