By Dana Downie
Jul 12, 2005
USDA/ARS scientists in Peoria, IL have devised a new DNA-based test machine for identifying deadly bacteria that is faster, easier to use and more precise than some methods currently used by food and beverage processors, according to an ARS press release.
Scientists say they have developed a “flow cytometer” that can handle up to 100 samples at a time and accurately identify Listeria monocytogenes and Candida albicans bacteria within a day.
The new machine also targets variations of the bacteria, says Todd Ward, a microbiologist who helped develop the system. Such variations can help distinguish one strain of Listeria from another.

By targeting genes for virulence, the test could enable a user to understand what makes some strains more harmful or better adapted to a particular environment than others. This could prove especially useful in HACCP programs at food-processing plants, he stated. The current Listeria test takes about three days to produce a result.
“The ability to identify Listeria that have colonized (in) your production plant can help determine whether food products are contaminated before coming into the plant or within the plant by resident strains,” Ward stated in a report on the research.
The test could also be used to check for yeasts such as Candida that cause food and beverage spoilage. It could also speed the search for yeasts adept at fermenting cornstarch into ethanol or those used for the control of fruit-storage rots, he said. The USDA wants to collaborate with private firms to develop the resulting tests in kit form.