Food Engineering

Viruses unleashed on produce pathogens

March 22, 2003
Can viruses that infect and kill bacteria naturally be used to rid fresh-cut produce of Salmonella and other food-borne pathogens?

A pair of researchers at the Agriculture Research Service think so, and have already met with some success in a series of tests performed on fresh-cut apples and melons at the Produce Quality and Safety Laboratory in Beltsville, Md.

Since the small viruses, also known as phages, are very selective about their host bacteria, that target Salmonella and other food borne pathogens would presumably leave beneficial bacteria to multiply on produce and crowd out more deadly bacterial strains. Although phages are already under study to control pathogens in meat, poultry and eggs, ARS plant pathologists Britta Leverentz and William S. Conway are reportedly the first to extend the investigation to fruits and vegetables — both whole and fresh cut.

Baltimore-based Intralytix is providing the researchers with known phages for Salmonella Enteriditis, which has come to be associated with contaminated produce in the last decade. Thus far, the researchers have tested a cocktail of four anti-Salmonella strains on melons and apples under conditions simulating normal food processing and storage. The fresh cut apples were chosen for their high acidity and the melons for their low acidity. Each slice was inoculated with 1 million bacteria and 100 million phages.

While the apple's higher acidity reduced phage survival to the point where they had no discernable effect on pathogen numbers, the melons fared better. Salmonella was consistently reduced to by more than 1,000 fold on melon chunks stored at 40 to 50 degrees F, and more than a hundredfold on fruit stored at room temperature.

By comparison, chlorine must often be diluted to a point where bacteria is reduced in the 10- to 100-fold range, according to researchers.