Treating food products with viruses that target and kill bacteria – called bacteriophages – could significantly reduce concentrations of E. coli, a Purdue University study released this week shows.
An injection of "phages" nearly eradicated a toxin-producing strain of E. coli in contaminated spinach and ground beef, in some cases decreasing E. coli concentrations by about 99%.
The study suggests that bacteriophage treatment could be an effective tool to help ensure the safety of food products, said Paul Ebner, associate professor of animal sciences.
"Phage treatment is a way of harnessing the natural antibacterial properties of phages to limit E. coli and other important foodborne pathogens," Ebner said. "Applying this kind of therapy to contaminated foods will make them safer."
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In his study, Ebner used E. coli O157:H7, which caused more than 63,000 illnesses in U.S. in 2011 alone. Most E. coli infections are caused by eating undercooked meat contaminated with the bacteria, but outbreaks associated with fresh produce such as spinach are on the rise.
In the study, fresh spinach leaves and ground beef were injected with about 10 million cells of E. coli, a far greater amount than typically found in contaminated food products, Ebner said. The researchers then treated the food with a "phage cocktail," a liquid containing three kinds of phages selected for their ability to quickly and efficiently kill E. coli.
After 24 hours, the treatment had reduced E. coli concentrations in the spinach, stored at room temperature, by more than 99.9%. E. coli dropped by more than 99.8% and about 99.8% in spinach after 48 and 72 hours, respectively.
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In ground beef stored at room temperature, the phages cleaned up about 99% of E. coli bacteria within 24 hours. The number of E. coli in refrigerated and undercooked ground beef shrunk by about 68% and 73%, respectively.
"Bacteria have viruses just like we do," Ebner said. "We're taking what already exists in nature and concentrating it to have an impact on these bacteria."
According to Ebner, phages are the most abundant life forms on the planet, if you consider viruses to be alive. "You can eat thousands of phages just by licking your lips," he said.
Ingesting phages does not pose a threat to human health because phages are highly host-specific, only targeting certain types of bacteria, said Ebner.
"Phage therapy is a way of using microbes beneficially, similar to using probiotics in yogurt," he said.
Interest in phages on the rise
Interest in using phages as antibacterial treatments has increased with the rise of antibiotic-resistant bacteria. The host specificity of phages can be an advantage over broad-spectrum antibiotics, which can wipe out both pathogenic and beneficial bacteria, Ebner said.
He said phage therapy is not a substitute for antibiotics, but "it can be very effective when used at specific time points and for shorter periods."
The paper was published in the Journal of Animal Science, titled "Development of bacteriophage treatments to reduce E. coli O157:H7 contamination of beef products and produce."