‘Sugar-Glass’ Films Use Viruses to Kill Harmful Bacteria in Food

Food Quality & Safety Magazine, December 1, 2017 • By Karen Appold

Scientists at McMaster University have developed an antibacterial “sugar-glass” coating that has the potential to prevent any illness caused by pathogenic bacteria such as E. coli, Salmonella, Campylobacter, and Listeria.

The technique uses viruses known as “bacteriophages” or “phages” to specifically target single strains of these germs with a high degree of specificity, making these bacteria “sick” and eventually causing their death while leaving beneficial microbes unharmed.

“Phages are abundant in the natural environment and food; they are not harmful to humans because they only infect bacteria,” explains Carlos Filipe, PhD, professor and chair, Department of Chemical Engineering, McMaster University, Hamilton, Ontario, Canada, one of the researchers. Phages can be immobilized in a thin film deposited as a coating on top of packaging and they can remain infective for at least two months at room temperature.

The approach can be used to protect solid packaged food. Films can be applied to paper sheets used in deli stores to separate slices of meat and can also be applied to flexible plastic films wrapping vegetables, Dr. Filipe says. Moisture from these food products will dissolve the film and release the phages—contacting the food’s surface and providing protection against a specific bacteria.

“This film could prevent food contamination after manufacturing, protecting food products longer against cross-contamination,” says Claudia Narvaez-Bravo, PhD, DVM, MSc, assistant professor, Department of Food and Human Nutritional Sciences, University of Manitoba, Winnipeg, Manitoba, Canada. “It’s probable that sugar-glass films could be part of hurdle technology, combining more than one approach to eliminate foodborne pathogens.”

In addition to containing phages—the active agents responsible for killing the bacteria—the film is made from a solution consisting of two types of sugars—pullulan and trehalose—hence the name “sugar films.” Pullulan is a polysaccharide with outstanding film-forming properties, Dr. Filipe says. Trehalose is used in the food and pharmaceutical industries to protect labile molecules (such as protein) against the negative effects of drying.

Differences From Other Methods

The method differs from others using bacteriophages to kill foodborne pathogens because it can stabilize phages for long periods of time at room temperature in the surface of a packaging material, Dr. Filipe says.

Another difference, according to Dr. Narvaez-Bravo, is that this technology involves immobilized phages; the majority of phages intervention currently used are delivering phages via spray or immersion. The film could be a solution for food where water is not desirable.

A Few Challenges

The researchers are still working on how to make the film dissolve slowly once contacted with the food to provide a continuous supply of fresh phages to the food’s surface, Dr. Filipe says.

Dr. Narvaez-Bravo foresees several possible challenges with the novel film. “Phages are more efficient when they are in a solution because the chances to find a host are higher,” she says. “When phages are immobilized, the phage-host interaction can still occur, but it might be limited.”

In addition, if the food was already contaminated before the coating is applied, the coating might not be as effective. This is because pathogens can be harbored within the food matrix, where phages may be unable to reach their host while immobilized.

Another limitation is the development of phage-insensitive mutants; this problem could be avoided by using multiple phages (in the film) targeting different host receptors, Dr. Narvaez-Bravo concludes.