Researchers Developing Rapid Salmonella Test

AMES, IowaResearchers at Iowa State University are developing a new rapid test for detecting Salmonella in food, which can provide DNA sequencing-like results in a few hours rather than days.

The method starts with a rapid polymerase chain reaction (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, SNAP71 (a reagent developed by Advanced Analytical Technologies, Inc.) is added, and the DNA is heated for 10 minutes at 100 degrees C. This reaction chemically cuts the labeled Salmonella DNA at all adenine and guanine sites (As and Gs) 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 by sieving them through a polymer matrix contained in glass capillaries that are 50 micronsnot much thicker than a human hair. 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 thats 300 bases long, this separation and detection process takes approximately 90 minutes.

Because the SNAP71 reagent cleaves the Salmonella DNA only at adenine and guanine, and not at thymine and cytosine sites (Ts and Cs), the method is not a direct replacement for DNA sequencing. Instead, the process rapidly generates a reproducible pattern of DNA fragments. Salmonella strains having slightly different DNA sequences within a given gene will yield different patterns of fragments, allowing discrimination of different strains of Salmonella.