A new phage may help control pathogens on fresh-cut produce. (EH Update).

Those fresh-cut fruits and vegetables in the grocery store are convenient, but they also have the potential to become another channel for human pathogens. So two Agricultural Research Service (ARS) scientists are testing the concept of using phages--viruses that infect and kill only bacteria--to control foodborne pathogens on produce. Early results are promising.

ARS plant pathologists Britta Leverentz and Bill Conway have been 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.

The scientists are working under a cooperative agreement with Intralytix, of Baltimore, Maryland, 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 freshcut 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, which have higher acidity. The phages consistently reduced Salmonella more than a 1,000-fold on melon chunks stored at 40[degrees]F and 50[degrees]F, and more than 100-fold on fruit stored at room temperature.

Those results come closer to the industry's goal of the 100,000-fold reductions than occurs with chlorine and other sanitizers now in use. The food industry is looking for alternatives because bacteria are developing resistance. Also, chlorine can be irritating to users, and solutions are often too dilute to reduce bacteria more than 10- to 100-fold.

On apples, the cocktail was ineffective. 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 2001 issue of Agricultural Research and online at <http://www.ars.usda.gov/is/AR/archive/julo1/phage070l.htm>.