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Photo: Electron micrograph of a Salmonella phage isolated from the Inner Harbor in Baltimore, Maryland. Link to photo information

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Controlling Pathogens on Fresh-Cut Produce--a New Phage?

By Judy McBride
July 30, 2001

Those fresh-cut fruits and veggies in your grocery store are convenient and nutritious. But they have the potential to become another channel for human pathogens. So two Agricultural Research Service scientists are testing the concept of using phages--viruses that infect and kill only bacteria--to control foodborne pathogens on produce. And early results are promising.

ARS plant pathologists Britta Leverentz and Bill Conway are the first to test phages on fruits and vegetables. While the peel or rind of intact fruit provides a physical and chemical barrier, microbes can multiply rapidly on cut surfaces--especially if those surfaces are not too acidic and have warmed up to room temperature, according to Leverentz. She and Conway are based at the ARS Produce Quality and Safety Laboratory in Beltsville, Md.

The scientists are working under a cooperative agreement with Intralytix in Baltimore, Md., which is providing known phages for Salmonella strains as a model. Phages are very selective about their host bacteria. Those specific for Salmonella, for instance, would leave beneficial bacteria free to multiply on fresh-cut produce and crowd out potential pathogens.

The researchers tested a cocktail of four anti-Salmonella phages on fresh-cut melons, which have low acidity, and on apples, with higher acidity. The phages consistently reduced Salmonella more than a thousandfold on melon chunks stored at 40 and 50 degrees F, and more than a hundredfold on fruit stored at room temperature.

That’s closer to the industry’s goal of the 100,000-fold reductions than occur with chlorine and other sanitizers now in use. The industry is looking for alternatives because bacteria are developing resistance, and chlorine can also be irritating to users. For that reason, solutions are often too dilute to reduce bacteria more than 10- to 100-fold.

On apples, the cocktail was ineffective. But the researchers are looking for acid-tolerant phages or a way to buffer the inoculum for high-acid produce. An article on this research appears in the July issue of Agricultural Research magazine.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.