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Studies to understand how Listeria monocytogenes bacteria colonize and spread on cabbage leaves could lead to new food safety practices.

ARS researchers are looking at varying abilities of bacteria strains to grow on vegetables such as this broccoli sprout, where green fluorescence indicates the presence of Listeria monocytogenesthree days after innoculation in the lab. Photo courtesy of Lisa A. Gorski.

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Pathogen Genes Targeted in Studies to Protect Salad Veggies

By Marcia Wood
July 2, 2008

No one knows exactly how microbes like Listeria monocytogenes or Salmonella enterica can attach themselves to the bumpy leaves of a cabbage or the ultra-fine root hairs of a tender young alfalfa sprout.

It's a mystery that Agricultural Research Service (ARS) food safety scientists in Albany, Calif., are intent on solving. The work, based at the ARS Western Regional Research Center, may lead to new ways to protect cabbage, sprouts and other salad favorites from attack by foodborne pathogens.

Microbiologist Lisa A. Gorski, for instance, led an investigation several years ago that was the first to document the genes that L. monocytogenes uses during a successful invasion of cabbage leaves. Gorski did the work with Albany colleague Jeffrey D. Palumbo and others.

Though scientists elsewhere had looked at genes that this Listeria turns on--or "expresses"--when it's grown on a bed of gel-like agar in a laboratory, no one had, at the time of Gorski's investigation, ever documented genes that this microbe expresses when it grows on a vegetable.

Listeria is perhaps best known for establishing colonies in humans, not on green plants. But the team found that Listeria, when invading cabbage, calls into play some of the same genes that plant-dwelling microbes routinely use to colonize and spread harmlessly on plants.

In newer work, Gorski wants to pinpoint genes responsible for the widely varying ability of eight different Listeria strains to successfully colonize the hair-thin strands, called root hairs, of alfalfa sprouts.

She's also interested in studying, and disabling, genes that help some Listeria colonies resist being washed off by water.

Read more about the research in the July 2008 issue of Agricultural Research magazine.

ARS is a scientific research agency of the U.S. Department of Agriculture.