By Jan Suszkiw
July 13, 2005
Identifying harmful yeasts and bacteria is faster, easier and more sensitive than current detection methods, thanks to a new test by Agricultural Research Service scientists in Peoria, Ill.
As a research tool, the new method’s use could shed light on what makes some strains of the bacterium Listeria monocytogenes more pathogenic than others. In food-processing applications, the test’s use could help redirect critical-control-point programs to better prevent contamination at manufacturing plants. Listeria’s disease-causing strains are the leading cause of food recalls due to microbial contamination.

On the medical front, the test may enable hospital clinicians to cast a broader net for the 30 to 40 species of Candida yeast that can infect humans, especially people with weakened immune systems. That’s according to Todd Ward, Brent Page and Clete Kurtzman, members of the team that developed the test in studies at ARS’ National Center for Agricultural Utilization Research in Peoria.
Pulsed-field gel electrophoresis (PFGE) is considered the gold standard for genetically identifying Listeria bacteria that cause food poisoning. But it’s difficult to run and time-consuming, among other disadvantages, according to Ward, a microbiologist in the ARS center’s Microbial Genomics and Bioprocessing Research Unit. The new test can be performed in a single day and distinguishes one Listeria strain from another based on nucleotide variations in their genes.
According to Page, a molecular biologist in the unit, culture-plate testing methods are now used to diagnose Candida infections. But such methods only detect a few key species, like C. albicans. Also, the turnaround time on results can be 24 hours to a few weeks, delaying treatment. Genetic fingerprinting methods used by some labs are faster, but they too detect only a few Candida species. The Peoria team’s test can identify 32 species, and it does so simultaneously in five hours or less.
Read more about the research in the July 2005 issue of Agricultural Research magazine.