Researcher Ching-Hsing Liao developed and tested a method that pits beneficial bacteria against potentially harmful ones. Bell peppers were dipped in solutions of water containing some of these beneficial bacteria. One bacterium, Pseudomonas fluorescens (Pf) 2-79, was particularly effective.
In 2006, E. coli nearly devastated spinach growers. This year, a Salmonella scare almost ruined the season for tomato growers. With global concern over U.S. food scares, many fear that the situation has reached critical mass; but a new food safety treatment developed by Ching-Hsing Liao, a microbiologist for USDA’s Agricultural Research Service (ARS), may help.
Liao developed and tested a method that pits beneficial bacteria against potentially harmful ones. The beneficial bacteria inhibit the growth of pathogens that survive initial physical or chemical attempts to remove them from fresh produce, thus increasing the effectiveness of conventional produce sanitation methods.
“Biological treatment as demonstrated in our study can only be used as a complement to the conventional treatment,” Liao says. “Biological treatment can only suppress the growth of the pathogen but does not kill the pathogen. If the initial number of pathogens on naturally contaminated produce is high, application of biocontrol by itself would be able to eliminate or reduce the pathogen number to a non-harmful level; however it cannot replace conventional chemical or physical treatments.”
Liao identified three beneficial antagonists for use in food safety intervention. He dipped bell peppers in solutions of water containing beneficial antagonists and examined the effect on surface pathogens including Salmonella and E. coli.
An Effective Solution
One bacterium, Pseudomonas fluorescens (Pf) 2-79, was particularly effective. Dipping peppers in a Pf 2-79 solution for two minutes halted pathogen multiplication almost entirely.
“Conventional treatment either by chemicals or physical forces can only reduce 90% to 99% of the pathogens on produce,” Liao says. “Pathogens that survive the treatment can renew the growth on produce to a level capable of causing illness. If beneficial bacteria or biological control agents are applied following chemical or physical treatment, they will suppress the growth of survivor pathogens.”
On untreated peppers, pathogen populations multiplied 100,000 times when stored at 68°F for two days, but treating peppers with Pf 2-79 suppressed pathogen growth.
“Since the number of Pf 2-49 introduced onto produce is at a level much higher than the number of pathogen on naturally contaminated produce or on produce that has received other intervention treatment, robust proliferation of Pf 2-79 on inoculated produce is expected to deplete all the space or nutrients required for the growth of pathogens, or competitive exclusion,” says Liao.
The Pf 2-79 dip also suppressed the growth of spoilage or soft-rotting bacteria on bell pepper and reduced the incidence of soft rot, which indicates the treatment would not only improve the safety but also the quality of produce, according to Liao.
Because Pf 2-79 is easy to grow, the cost would be affordable once Liao and his colleagues can prove the economic benefit, he says. The treatment would be best done at produce packaging or processing plants by adding powder or liquid form of Pf 2-79 directly into a water wash tank or spraying produce with the solution, according to Liao. A regulatory approval through FDA or EPA may be required before the strain of Pf 2-79 can be used for field and commercial testing, he says.
Liao and his colleagues plan to validate the research on a larger scale, as well as identify additional bacterial strains that could be used with Pf 2-79 to further improve produce safety and quality.
“We are in the process of evaluating if mass application of Pf 2-79 would cause any sensory or flavor/aroma change on treated produce, although no indication of such undesirable effect has been observed so far,” Liao says.