Pitting Microbe Against Microbe for Safer Foods
By Rosalie Marion
March 16, 2007
Before fresh fruit is cut, it's
important that the outer skin be kept free from foodborne pathogens. That's
because food-contaminating microbes on the surface of a peel or rind could
piggyback onto a cutting knife and be dragged into the fruit's flesh.
Agricultural Research Service (ARS)
scientists have led a team that tested a combination of bacterial enemies that
effectively controlled Listeria monocytogenes on fresh-cut honeydew
melon pieces during exposure tests.
L. monocytogenes is a foodborne human pathogenwidely
distributed in naturethat tolerates environmental stress, multiplies at
low temperatures and survives refrigeration. It can cause serious infections.
And federal agencies have established a zero-tolerance for L.
monocytogenes in processed, fresh-cut fruits and vegetables.
Conway, with the
Produce Quality and Safety Laboratory at Beltsville, Md., and
Janisiewicz, with the
Appalachian Fruit Research Station at Kearneysville, W.V., led the study.
They worked in cooperation with Baltimore, Md.-based
To test bacteria-fighting potential, the researchers treated honeydew melon
pieces with three different protective solutions: either an oxidative bacterium
known as Gluconobacter asaii, a mixture of six L.
monocytogenes-specific bacteriophages or a combination of both.
The G. asaii bacteria are naturally present on the surface of pome
fruits, such as apples and pears, and are nontoxic to humans. Bacteriophages
are viruses that, while nontoxic to humans, kill specific human bacterial
After artificially contaminating the test honeydew pieces with L.
monocytogenes, the team found that the combination of phages and G.
asaii bacteria was the most effective treatment. It reduced L.
monocytogenes populations by more than 99.9 percent.
more about the research in the March 2007 issue of Agricultural
ARS is the U.S. Department of
Agriculture's chief scientific research agency.