The Food and Drug Administration has approved phages for use in foods – but only against Listeria monocytogenes, notes food microbiologist Ipek Goktepe of North Carolina Agricultural and Technical State University in Greensboro. And these products find use primarily on meat and deli products, she added. But that's not bad, since Listeria is one of the most common food-poisoning agents. And a particularly recalcitrant one since it happily grows at refrigerated temperatures. Goktepe reported new data showing that Listeria phages aren't uniformly effective in protecting every contaminated food to which they're applied. Food producers would like to see at least a "4 log" reduction in bacteria – that is, a reduction to one ten-thousandth of the starting population of bugs. In some of Goktepe's tests, she may see a three log reduction or less.One recent success: An E. coli phage that targets O157:H7 strains killed a huge share of these bacterial cells that had been growing on loose lettuce and spinach leaves. When the phages were applied in a moist mist, Goktepe says, "We achieved a 3 to 7 log reduction – and that's a lot. We were not expecting that," she says. "Usually a 4 log reduction is considered very significant." She cautions that the big bacterial drop occurred under fairly ideal conditions, such as at 3 °C, a good refrigerator's temperature. Raise the leafy greens' temperature to 10 °C (about 50 °F) and the phage delivered only a 2 to 5 log drop in E. coli numbers.
The phage treatment against both Listeria and E.coli 0157:H7 opens up new avenues for protecting foods against serious microbial contaminants and it should be possible to evolve species-specific phages for widespread use by the industry. Phages occur in abundance in soil, water,sewage,feces,retail foods, process plant effluents from which high titer purified lysates can be made. Most studies have concentrated on Salmonella, Listeria. Campylobacter and Enterogenic E.coli. Typical applications include pre and post harvest spraying on animals like chickens, piglets, calves and lambs. Use of phages in refrigerated foods like fruits, dairy products, poultry products and meat has been found to be good bio-control strategy for extending their shelf life. The technique is self perpetuating, highly discriminatory, natural and cost-effective. Limitation of the phage technology include limited phage range, requirement of threshold number, phage resistant mutants and potential for transduction of undesirable characteristics from one strain to another. How far the technology can be made acceptable to the consumer is a critical question that does not have an answer to day.