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Garden microbe foils E. coli O157:H7 in laboratory tests

A microbe that may be living peaceably on the beans and cucumbers in backyard gardens might someday be recruited to foil foodborne pathogens. Agricultural Research Service (ARS) geneticist Michael B. Cooley looked at the pathogen-fighting abilities of the farm- and garden-friendly microbe, Enterobacter asburiae, in studies begun in 2002.

In his laboratory at the ARS Western Regional Research Center in Albany, Calif., Cooley showed that E. asburiae can significantly reduce the levels of two pathogens — Escherichia coli O157:H7 and Salmonella enterica. That happened when Cooley inoculated seeds of thale cress, a small plant often chosen for laboratory tests, with all three species of microbes.

The study, published in Applied and Environmental Microbiology in 2003, led to follow-up experiments with green leaf lettuce. In that "battle of the microbes," another rather ordinary bacterium, Wausteria paucula, befriended E. coli and enhanced its survival six-fold on lettuce leaves. The finding represented the first clear example of a microbe's supporting a human pathogen on a plant, according to Cooley.

Adding E. asburiae to the experiment again demonstrated this beneficial microbe's ability to suppress E. coli. When lettuce leaves were exposed to the three kinds of microbes, E. asburiae decreased E. coli survival 20- to 30-fold.

Cooley, who documented those findings in the Journal of Food Protection in 2006, noted that the mechanisms underlying the competition between E. asburiae and E. coli are still a mystery. In particular, more remains to be learned about the competition that takes place — among the microbes — on leaves or other plant surfaces.

In the meantime, E. asburiae shows initial promise for use as a biological control agent in science-based strategies to safen salad greens, Cooley reports.

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

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