Sensor detects heat-resistant toxins.

Regulatory agencies and the food industry need fast, automated, cost-effective analytical methods that are accurate, reliable, and safe and that minimize waste. Today, chemists are using advanced technologies to develop processes that screen, detect and confirm multiple chemical residues, such as veterinary drugs and pesticides, pathogenic bacteria and toxins in foods.

A new sensing technique developed by USDA-ARS scientists is able to detect heat-resistant toxins in such products as ham, milk and eggs. The technology, which is not patented and is in the public domain, should help researchers and inspectors detect toxins that cause gastroenteritis.

Investigators have developed a biosensor that detects chemical signals from toxin-producing bacteria and provides information about their specific biological activities. Bacteria produce toxins under stressful conditions, such as when they are too crowded, denied food or are fighting against antibiotics. Generally, conventional heating and processing kill foodborne bacteria but do not destroy their toxins.

Researchers focused on S. aureus enterotoxins A (SEA) and B (SEB). The biosensor makes use of a surface plasmon resonance (SPR) to detect toxins. SPR uses light reflected off thin metal films. Attached to these films are toxin or antitoxin antibody molecules. When these molecules bind to the film surface, they change the way light refracts. These changes in light intensity, monitored by an optical detector, provide a measure of how much toxin is present in a sample.

One potential use for the technique would be to detect enterotoxins in liquid whole eggs. The semi-automated method will be able to detect several bacterial toxins in a single sample. In addition to detecting bacteria and their toxins, the ARS chemists are developing methods to screen, detect and confirm multiple chemical residues, such as veterinary drugs and pesticides, in foods.

Investigators also developed a latex particle agglutination assay for detecting SEA and SEB that cause toxins to clump together. The method takes advantage of an antibody's ability to bind to a unique antigen in pathogen cells. The assay is simpler to use than other methods and can detect as few as 10 parts per billion of toxin per gram of sample.

The technique for detecting the enterotoxins in eggs will be tested with commercial liquid eggs. The ARS Food Safety and Inspection Service will determine if the on-site test will be used in processing facilities. Further information. Marjorie Medina, USDA-ARS Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, PA 19038; phone: [phone]; fax: [phone]; email: [e-mail].