A faster way to test for egg safety

Last summer, an outbreak of salmonella sickened hundreds of people across the country and led to a nationwide recall of some 550 million poultry shell eggs. Salmonella bacteria can cause serious and sometimes fatal infections in young children, frail or elderly people and others with weakened immune systems.


Federal regulators monitor egg quality, but traditional laboratory tests take, at minimum, 10 days to confirm the presence of Salmonella Enteritidis in eggs. And the long delay means potentially contaminated eggs are often shipped and sold to consumers days after the contamination originated.

Now, a collaboration between Penn’s School of Veterinary Medicine and a life science company based in California has led to the launch of a new, faster DNA-based detection kit that tests for salmonella in poultry eggs. The kit reaches accurate results in about 27 hours, and will enable major egg producers to meet the Food and Drug Administration’s new stringent testing standards for eggs, which went into effect in July.

For Penn’s Shelley Rankin, FDA approval of the kit was a dream more than 15 years in the making. Rankin, an associate professor of microbiology at Penn Vet, says she initiated work to develop a new, quicker test after learning about the revised federal guidelines for egg quality assurance.

Pennsylvania has long history of ensuring egg quality. In 1992, it was the first state to initiate a voluntary egg quality assurance program, and Rankin’s colleagues at the Pennsylvania Animal Diagnostic Laboratory System—Penn State will be the first to implement this new level of testing. The Penn Vet laboratory also contributed to the work.

To develop the new test kit, Rankin teamed with a company called Life Technologies, which has experience working with the genetic-testing technique known as real-time polymerase chain reaction, or PCR, to detect salmonella inside of eggs. Life Technologies designed the assays and protocols. Rankin’s lab validated the protocol and performance. Penn Vet Research Specialist Kathleen O’Shea led the efforts in Rankin’s lab.

The entire process took just over a year to complete. The result is a much faster and effective method for testing eggs. Neither Rankin nor Life Technologies was paid to do the work, and Penn and Life Technologies absorbed the costs of the project.

“I wanted to be able to stand behind the test we developed because it is the best kit, rather than we get paid to do the work,” says Rankin.

But, she adds, more work remains. The FDA approval was for testing liquid eggs. A kit that could deliver fast and accurate results for samples taken from the environment where the birds are kept could help producers detect salmonella even sooner, Rankin says.

“I’m hoping that as we move along over the next couple years that we’ll improve this kit: Can we get the time down to 12 hours instead of 27 hours?” she asks.

“There [are] some amazing techniques out there right now that might actually take this over at some point and allow us to do testing of a lot more samples than we test currently for a much-reduced cost,” Rankin says. “This is something my lab is going to be working on for several years to come.”

Originally published on February 17, 2011