Fluorescent Sensor Simplifies, Speeds Up Pathogen Detection

A new fluorescent test system called a DNAzyme sensor, developed by researchers at Toronto’s McMaster University, may speed up and simplify the detection of pathogens such as Salmonella and E. coli by hunting for the metabolic DNA byproducts left behind by these bacteria. (DNAzymes are synthetic one-stranded DNA molecules with catalytic activity.)

In an analysis published in Angewandte Chemie International Edition (2011; 50(16):3751–3754 [http://onlinelibrary.wiley.com/doi/10.1002/anie.201100477/abstract]), investigators reported that the probe requires just 12 hours to accurately detect E. coli, compared with approximately two days for conventional methods.

“We haven’t yet published the Listeria probe, but we now have it to about 30 hours versus the current test that takes about five days,” said lead researcher Yingfu Li, PhD, assistant professor in the departments of biochemistry and chemistry. “Our goal is getting to about seven to eight hours on all pathogens, although we haven’t achieved that yet.”

To develop the probe, Dr. Li and his team hypothesized that at the point when a cell is cultured, it would generate markers. “They would take in these nutrients and ‘spit out’ molecules they don’t want, leaving a DNA trail that we could detect,” he said. The probe they created for E. coli, for example, binds to a specific metabolic product from that bacteria and forces the DNAzyme to change its shape. Thus altered, the DNAzyme begins to fluoresce.

“We should be able to find a specific DNAzyme for any pathogen,” Dr. Li said. He likens the DNAzyme development process to “American Idol.” “We start with a pool of hundreds of thousands of potential talents,” he said. “We know there are a lot of possibilities out there, but through a lot of judges and competitions, it’s whittled down to one ‘American Idol.’ By using intended bacteria targets and applying this principle, that’s how we generate the ideal molecule we identify.”