story to find out more.
Medina prepares egg samples for analysis of Staphylococcus aureus
enterotoxins by surface plasmon resonance. Click the image for more
information about it.
New Detection Methods Improve Food Safety
By Jim Core
January 6, 2005
A new technique developed by the Agricultural Research Service (ARS) to detect heat-resistant toxins in
foods such as ham, milk and eggs should help researchers and inspectors detect
toxins that cause gastroenteritis.
B. Medina, a research chemist at the ARS
Regional Research Center in Wyndmoor, Pa., developed a biosensor-based
method 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 fighting back against antibiotics. Generally,
conventional heating and processing kill food-borne bacteria but do not destroy
In her studies, Medina focused on Staphylococcus aureus
enterotoxins A (SEA) and B (SEB). Her biosensor test makes use of what's called
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, if any, is present in a food
One potential use for the method would be to detection enterotoxins in
liquid whole eggs. Medina's semi-automated method will be able to detect
several bacterial toxins in a single food sample.
In addition to detecting bacteria and their toxins, Medina and other
chemists at the Wyndmoor center are using advanced technologies to develop
methods to screen, detect and confirm multiple chemical residues--such as
veterinary drugs and pesticides--in food products.
about this research in the January issue of Agricultural Research
ARS is the USDA's chief scientific