Controlling Pathogens on Fresh-Cut
Produce--a New Phage? By
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
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
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.
Thats closer to the industrys 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
Agricultures chief scientific research agency.