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Dennis D'Amico, a professor of animal science at the University of Connecticut, demonstrated that bacteriophages can successfully reduce the levels of common food pathogens in milk.
Each bacteriophage is highly specific and acts only on certain genera or species of bacteria, and in some cases - only on a specific strain.
"If you have a target, such as a food pathogen, for example, E. coli, then there are phages that infect only E. coli. This means that no beneficial bacteria in your gut or food will be affected, and your human cells will not be touched," he explains.
Bacteriophages are organic antibacterial agents that do not alter the color, taste, or texture of food.
"Manufacturers strongly support the use of phages because it is a natural approach," says D'Amico. He studied several phages available for sale that target common pathogens transmitted through dairy products, such as listeria, salmonella, and E. coli. The goal was to determine how effectively they reduce the levels of these bacteria in milk and cheese. The research results were published in the journal Food Microbiology.
Each product tested by D'Amico contained a mixture of phages targeting specific types of pathogens or strains.
"You mix a lot of these phages, hoping to cover all possible strains that may be present in your food product," says D'Amico.
D'Amico noticed a significant reduction in the levels of pathogens in pasteurized milk. The effects were noticeable within a few hours and continued for up to a week. The amount of listeria decreased by 10,000 times compared to the control group. Regarding E. coli, the effect was more complex, as the levels of some strains decreased by only five times, while others decreased by 100 times. However, with raw milk, the situation was different.
In raw milk, the phages did not reduce the levels of Listeria or E. coli. In fact, the number of phages decreased. This happens because the heat used in pasteurization changes the structure of proteins that could otherwise hinder the phages. In raw milk, these proteins bind to the phages and prevent them from reaching the target - the bacteria.
Regarding salmonella, phages effectively reduced the levels of this pathogen in both pasteurized and raw milk. In pasteurized milk, the pathogen levels decreased by 200-1500 times. In raw milk, the reduction was more moderate, but still significant - from 13 to almost 200 times. These results were also published in the journal Food Microbiology.
D'Amico did not observe a significant decrease in either semi-hard cheese or soft fresh cheese.
"Cheese is a process of turning liquid into a solid. Now these phages and bacteria are in one place, and their ability to interact is greatly reduced. Therefore, we noticed a significant decrease in their effectiveness in the cheese-making process," says the researcher.
However, in sour cream treated with phages, a moderate reduction in the levels of pathogens was observed compared to the control group.
"If we go back, there was a weak effect when phages are added during the cheese-making process, and this difference between treatment and control persists throughout the period," says D'Amico. "Our goal was to enhance the impact during cheesemaking, as phages are likely to remain effective throughout the storage process."
The main constraint of using bacteriophages to combat pathogens in dairy products remains their high cost. To achieve the results in milk that D'Amico obtained, it was necessary to add 1,000,000 times more phages than pathogens.
Considering that bacteriophages are relatively expensive, this poses a serious obstacle to their widespread use, especially for small producers.
"There were a million times more phages than bacteria. From a health and product quality perspective, this doesn't matter, but in terms of costs, you have to add quite a lot of phages to achieve the effect we observed," he concluded.
