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Collaborate on faster salmonella detection technique.

Scientists at Iowa State University are collaborating with a local analytical company on a faster method for detecting and genetically identifying Salmonella in contaminated foods. The goal is to replace the current system of Salmonella detection with a new approach that can provide DNA sequencing-like data in hours, rather than days.

Currently, definitive genetic identification of food-borne pathogens is done using traditional DNA sequencing methods first developed in the 1980s, which indicate whether Salmonella is present. But further details are lacking, including the type of strain present. This requires additional work, which entails waiting about two days for results.

The method being developed at Iowa State starts with a rapid PCR reaction that amplifies a Salmonella-specific gene, generating millions of fluorescently labeled copies of this DNA in about 20 minutes. Next, instead of cycle sequencing, the PCR product is purified for five minutes. Then, SNAP71, a reagent developed by Advanced Analytical Technologies Inc, Ames, IA, is added, and the DNA is heated for 10 minutes at 100 C. This reaction chemically cuts the labeled Salmonella DNA at all adenine and guanine sites in the DNA chain.

The result is a complex soup of fluorescently labeled DNA fragments of all sizes. These fragments are then separated in a high-voltage electric field. This process separates the DNA fragments according to their size, from smallest to largest, and each piece is detected as it passes in front of an intense light source. For a PCR product that's 300 bases long, this separation and detection process takes approximately 90 minutes.

Because the SNAP71 reagent cleaves the Salmonella DNA only at the adenine and guanine sites, and not at thymine and cytosine sites, the technique is not a direct replacement for DNA sequencing. Instead, the process rapidly generates a reproducible pattern of DNA fragments. Salmonella strains with slightly different DNA sequences within a given gene will yield different patterns of fragments, making it possible to discriminate among different strains of Salmonella. The entire process can be accomplished in about two and a half hours.

Further information. Byron Brehm-Stecher, Department of Food Science and Human Nutrition, 3344 Food Science Building, Iowa State University, Ames, IA 50011; phone: 515-294-6469; email:
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Publication:Emerging Food R&D Report
Date:Jun 1, 2012
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