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A slice of queso fresco might seem harmless, but in some instances, it can carry a deadly hitchhiker: Listeria monocytogenes. As Hispanic-style cheeses gain popularity in U.S. kitchens, scientists are working to ensure their safety. Traditional methods to curb Listeria have limits, so researchers are turning to an unexpected ally: viruses that hunt bacteria.

In the battle against foodborne illness, scientists are turning to an unlikely ally: bacteriophages, viruses that infect bacteria. A recent Journal of Biological Chemistry details the structure and function of PlyP100, an endolysin from bacteriophage P100.

Researchers from the labs of , professor of food microbiology at the University of Illinois Urbana–Champagne, and , professor of biochemistry at Stockholm University, combined their expertise in food safety and novel protein characterization to study PlyP100. Co-first authors Karson Bateman and Emma Scalleti Hutchinson said the P100 bacteriophage is already used in food production, so PlyP100 could be commercialized to prevent Listeria in queso fresco.

PlyP100 is an endolysin, a protein bacteriophages use to break down bacterial cell walls.

"With Gram-positive bacteria, it is possible for endolysins to hydrolyze the surface exposed peptidoglycan when added exogenously which makes then an interesting tool for controlling unwanted, Gram-positive bacteria," Miller said.

Few endolysins have been studied in detail, so identifying the best candidates for food safety remains trial and error, Bateman said. To move beyond trial and error, the team used AlphaFold to predict PlyP100’s 3D structure, revealing three domains.

Domain 1 proved key for hydrolytic activity, the team confirmed by testing mutated versions in lab models, including queso fresco. They found domain 3 binds Listeria’s cell wall and discovered an unexpected role for domain 2.

“The second domain does not seem to have a discrete function, yet it is still necessary for full function of the endolysin," Scaletti said. "The importance of domain 2 was a bit of a surprise but this demonstrates why experimental validation is still needed.”

This structural insight could enable computer-based analysis of uncharacterized endolysins and expand their use.

"We anticipate that work like this will enable analysis of uncharacterized endolysins identified in genomic sequence databases and facilitate greater application of these powerful proteins," Stenmark said.

Next, the team plans to produce PlyP100 in a GRAS, or a Generally Recognized as Safe, organism, such as yeast, to test conditions to keep it active in queso fresco and study synergy with other antimicrobials.

Food safety affects everyone, from farmers to families at the dinner table. By unlocking the secrets of PlyP100, researchers are moving beyond trial and error toward precision tools that could stop deadly outbreaks before they start. If successful, this work won’t just protect queso fresco lovers — it could redefine how we safeguard the global food supply.