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Discovering a new method to 
identify Salmonella

A new approach may be able to reduce the time it takes health officials to identify Salmonella strains by more than half, according to researchers in Penn State’s College of Agricultural Sciences.

The finding may significantly speed up the response to many outbreaks of foodborne illness, and help investigators more quickly find and eliminate the source of the disease.

“There are more than a million estimated cases of salmonellosis annually in the United States, resulting in 
approximately 400 deaths, nearly 20,000 hospitalizations, and an economic burden of millions of dollars,” said study lead author Nikki Shariat, postdoctoral researcher in molecular microbiology in the Department of Food Science. “Right now, public-health laboratories use a technique called pulse field gel electrophoresis, or PFGE, to subtype Salmonella strains, and it normally takes one to three days to identify a specific strain. The technique we devised often takes just one day.”

Working under the direction of Edward Dudley, associate professor and the Casida Development Professor of Food Science, Shariat developed the new approach to identify strains of the Salmonella serotype Newport. The method focuses on two virulence genes and two novel regions of Salmonella DNA called clustered regularly interspaced short palindromic repeats, or CRISPRs. The researchers devised a method of multi-virulence-locus sequence typing, or MVLST, that can detect strain-specific differences in the DNA at these four locations. The researchers designated the method as CRISPR-MVLST.

“The significance of our work is not just that we can subtype Salmonella strains in half the time or less compared to the protocol that is used right now,” she said, “but also our approach is very comparable in terms of the data—our method yields results that are accurate and similar to the PFGE method now widely used.”

The CRISPR-MVLST method also is likely to be much cheaper, she suggested. Shariat explained that the new method is different because it looks at the DNA sequence, whereas the other method basically cuts the DNA into small pieces with no actual sequence information.

“Fifty percent of bacteria have CRISPR regions, and using these for identification has been done with quite a few bacteria, such as Mycobacterium tuberculosis, as well as with some that cause foodborne illness, such as Campylobacter and E. coli,” Shariat said.

Jeff Mulhollem