Researchers developing more accurate salmonella subtyping after egg recall

By Caroline Scott-Thomas

- Last updated on GMT

Related tags: Dna, Salmonella

Researchers at Penn State’s College of Agricultural Sciences have said they are developing a method to more accurately identify salmonella strains – which could help scientists identify the source of an outbreak sooner.

Salmonella enteriditis was behind the egg recall that led to the withdrawal of about 550m eggs from the market, with 380m recalled by Iowa-based Wright County Egg, and a further 170m pulled from the market after the strain was also linked to Hillandale Farms – another Iowa facility – a week later. However, according to the Centers for Disease Control and Prevention (CDC), about 1,300 reported illnesses were likely to be associated with the outbreak before the recalls began.

In a conference call with reporters last month, acting director of the CDC’s division of foodborne, waterborne and environmental diseases Dr. Christopher Braden said it was hard to say exactly how many illnesses were involved because of the particular salmonella strain associated with the outbreak.

Penn State researchers are hoping to prevent this situation.

Professor of food science at Penn State Stephen Knabel said: "The problem is that different strains of salmonella enteritidis are highly related and very difficult to distinguish between. The CDC uses a method of DNA fingerprinting called PFGE to track the strain that caused the outbreak, but it doesn't work so well with salmonella enteritidis."

He explained that the PFGE method to differentiate between strains is based on the patterns that occur in DNA fragments when chromosomes of the bacteria are digested with specific enzymes.

The approach being developed at Penn State instead looks at actual DNA sequences of specific genes, allowing scientists to more accurately pinpoint specific outbreak strains.

"We are hoping that the molecular subtyping method we are perfecting will allow scientists in public health labs to distinguish between different outbreak strains of salmonella, including salmonella enteritidis,"​ Knabel said. "CDC recently sent us 30 isolates associated with the current outbreak with the hope that our new method will help identify the true source of the salmonella enteritidis that caused this outbreak."

Penn State researchers have previously made a number of discoveries that have helped improve egg safety, including methods to prevent and detect salmonella enteriditis.

Knabel said: “We have dramatically increased our ability to detect, track and control salmonella enteritidis in shell eggs. And that protects both consumers and a very important food industry in Pennsylvania and throughout the United States."

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