An outbreak of salmonella in eggs that resulted in thousands of illnesses and a costly recall earlier this year could have been prevented with better testing. Current techniques, using culture samples in a Petri dish, can take up to five days to produce results, by which time the infected product is already in stores.
Using a DNA-based process, food scientists at the University of Missouri have developed a faster and more accurate way to test poultry and eggs for live salmonella contamination. The results are available in 2 to 5 hours, allowing poultry producers to detect contamination before the product is shipped.
“Processors and consumers will benefit from the speed and sensitivity of the new test’s results,” said Azlin Mustapha, associate professor of food science at the MU College of Agriculture, Food and Natural Resources, who developed the test. “This will keep companies from shipping contaminated products, and keep salmonella infected products out of consumers’ hands.”
Mustapha’s research allows scientists to use a DNA identification system known as polymerase chain reaction, or PCR, which amplifies a few pieces of DNA to several orders of magnitude. Large clumps of salmonella DNA are more easily detected and accurately measured.
Such PCR testing for food has been around for years, but results were difficult to interpret because it could not differentiate between dead and live salmonella DNA. Only live salmonella cells trigger the human disease of salmonellosis. Mustapha’s modification adds a dye that is absorbed by dead cells, which have weaker cell walls. The PCR test can be set up to ignore dead cells and replicate any live salmonella DNA for detection.
Salmonella is the most common cause of food poisoning in the United States, with about 40,000 cases reported each year, according to the Centers for Disease Control. In a recent outbreak involving eggs, approximately 1,813 illnesses were reported between May 1 and October 15, 2010, leading to a nationwide recall of eggs produced in an Iowa plant.
Salmonella can cause diarrhea, vomiting, fever and abdominal cramps. Infants, elderly persons and those with weakened immune systems are more likely to develop severe illness, in which salmonella spreads from the intestines to the bloodstream and other body sites. An estimated 400 people die annually from salmonella poisoning, according to the CDC.
The new test is important because salmonella contamination in poultry can be a difficult problem to address, Mustapha said. It can persist for a long time in both the spleen and reproductive tract of poultry. During the birds’ sexual maturation, salmonella can colonize both the ovary and the oviduct of hens, thus infecting all eggs produced as well as the chicken.
Mustapha said poultry and egg producers who want to adopt the new test will need to buy a PCR machine and train personnel in its use. Once installed, however, the system requires less labor and time than conventional testing techniques, resulting in long-term savings, she said. The USDA’s Food Safety and Inspection Service and the Missouri Department of Agriculture have shown interest in the newly developed process.
Mustapha worked with Luxin Wang, a graduate student in the food science program. Their research results were published recently in the Journal of Food Science.