Spray to kill harmful bacteria on food

The McMaster engineering team behind the invention, led by professors Zeinab Hosseinidoust, who holds the Canada Research Chair in Bacteriophage Bioengineering, and Tohid Didar, who holds the Canada Research Chair in Nano-Biomaterials, and graduate student Lei Tian, have created a spray using nothing but the microbeads.

The spray consists of microgel beads of viruses known as bacteriophages. Although the latter are harmless to humans, they kill and eat bacteria. And importantly, certain bacteriophages prey on certain types of bacteria – they don't just indiscriminately kill all bacteria, harmful and beneficial alike.

Building upon previous research by the same group, the process for producing the beads begins with the creation of a liquid solution made up of bacteriophages and a crosslinking organic compound called glutaraldehyde.

That solution is deposited onto a two-layer thin polymer film – the bottom base layer is solid, whereas the top template layer consists of a honeycomb-like grid of tiny holes.

Next, the solution-filled film is placed in a vacuum for 10 minutes, then left in a cool, humid environment for two days. Over this time, the glutaraldehyde causes all the individual bacteriophages in each honeycomb hole to self-assemble into linked nanofilament networks, thus forming a gelatinous bead in that hole.

When the top layer of the film is subsequently peeled off, the microgel beads can be harvested from the exposed base layer. Each bead is about 20 microns wide, and contains approximately half a million bacteriophages. In this collective form, the viruses are considerably more robust than they would be on their own.

"They link together like microscopic Lego pieces," said one of the lead scientists, Prof. Zeinab Hosseinidoust. "This organized natural structure makes them much more durable and easier to package, store and use."

In lab tests, the bead spray thoroughly eradicated E. coli bacteria on tainted lettuce and meat within nine hours of application. The scientists state that if other types of bacteriophages were used, the spray could also kill harmful bacteria such as Salmonella and Listeria.

It is hoped that the spray could ultimately be utilized when processing and packaging foods, or even when growing fresh produce. The technology could additionally have medical applications, being used to kill bacteria in infected wounds.

A paper on the research – which was co-led by Assoc. Prof. Tohid Didar and grad student Lei Tian – was recently published in the journal Nature Communications.

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