Two studies by researchers at the U.S. Department of Agriculture (USDA) and the Compton Laboratory in the U.K. have shown that phages may be useful in eliminating harmful bacteria from our food. Food-borne infections are very common. Millions of people each year get sick due to food contaminated with certain bacteria. These bacteria include Listeria monocytogenes, Campylobacter jejuni, and Salmonella enterica to name just a few. Listeria monocytogenes (L. monocytogenes)can in some people cause an infection of the brain that can be life-threatening. Campylobacter jejuni, and Salmonella enterica cause severe diarrhea. Diarrhea can be a real problem for people that become dehydrated and may require hospitalization to rehydrate them. The researchers at the USDA lab describe studies that involved using a phage that specifically kills L. monocytogenes on cut fruit. The cut fruit market is a growing enterprise in the United States. Many people prefer getting half of a melon they eat entirely than a whole melon of which half will go to waste before they can eat it. Unfortunately, cut fruit can become contaminated with L. monocytogenes during the cutting process. Storage of the cut fruit will not keep L. monocytogenes numbers down because this bacterium grows very nicely at refrigerator temperatures. Most decontamination processes will cause the fruit to taste funny ruining the fruit's retail potential. L. monocytogenes phages on the other hand only infect L. monocytogenes. They do not change the flavor of the fruit and do not infect humans. The researchers took fresh cut honeydew melons and Red Delicious apples and applied L. monocytogenes to the cut surfaces of the fruits. They found that L. monocytogenes would grow some on the apples but really grew well on the honeydew melons. They then sprayed the phages onto the L. monocytogenes contaminated fruit and found these bacterial viruses could significantly reduce the number of bacteria on the fruit. The killing of the bacteria was not complete with just the phage alone so they also added nisin along with the phage to the cut fruit. Nisin is a small protein obtained from lactic acid producing bacteria. It is also not harmful to humans. It is able to cause small pores to form in the bacterial membranes helping the phage to kill the bacteria. Nisin also appears to reduce the likelihood that L. monocytogenes will become resistant to the phage. When both phage and nisin are added to the fruit the levels of remaining L. monocytogenes are lower than can be achieved by chemical sanitizers or by washing with water.
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