Scientists at Purdue University have developed a nanoparticle capable of keeping food safe from Listeria contamination for significantly longer than has previously been possible.

The nanoparticle works by slowly releasing nisin, an antimicrobial agent that kills Listeria, into food.  Nisin is already commonly used to prevent the growth of Listeria.  However, it remains effective for only a few days before it begins to break down and wear off.

This is where the nanoparticle comes in.  It can keep nisin stable for an extended period by holding onto it and releasing it slowly over time.

“You can load large amounts of nisin into this material,” says Dr. Arun Bhunia, a microbiologist at Purdue and partner in the research.

As the nisin molecules get used up, more and more of them are released from the nanoparticle, Bhunia says.  The process helps the nisin to last significantly longer.

Bhunia explains that this discovery could be an important one for commercial food establishments such as delis, where Listeria has ample opportunity to contaminate meats during unpacking, slicing or storing steps. The nanoparticle could also be used effectively in packing plants, where ready-to-eat foods can easily become contaminated with Listeria.

The nanoparticle would likely be administered to food in the form of a spray.  Research has shown that the particle would then be effective for at least 21 days after spraying, and could even prevent Listeria for up to 40 or 45 days.

Finding a way to control Listeria is of critical interest to food producers, because although it is less common source of illness than other food pathogens, it is far more deadly.  It kills at least 16 percent of those it infects.  Pregnant women are 20 times more likely than healthy adults to get listeriosis, which is particularly lethal to fetuses–perinatal listeriosis results in stillbirth or neonatal death in about 25-50 percent of cases.

Makers of raw milk cheese and ready-to-eat foods like deli meats must carefully guard against it, because it can thrive at refrigerator temperatures.  In Canada, an outbreak of Listeria in deli meats resulted in at least 57 illnesses and 22 deaths.  In the U.S., it causes an estimated 1,591 illnesses and 255 fatalities each year.

But in addition to fighting Listeria, Purdue’s little nanoparticle could have an even bigger impact on food safety by combating other foodborne pathogens as well.  The nisin that it holds can also kill other gram-positive microbes, such as Staphyloccocus and Clostridium.  And, according to Bhunia, the nanoparticle has the potential to hold antimicrobials aside from nisin that could prevent the growth of gram-negative bacteria such as E. coli and Salmonella. 

The research team that developed the nanoparticle was funded by the U.S. Department of Agricutlture and the National Science Foundation.  The nanoparticle was developed by Dr. Yuan Yao, a chemist at Purdue, who produced it by altering the surface of a carbohydrate found in sweet corn.  

 “The beauty of this nanostructure is that it’s carb-based,” says Bhunia.  In this way, one food can serve to keep thousands of others free of contamination.