Bacteriophages, or phages, are viruses that infect and kill bacteria. These microscopic predators are found everywhere from soil and water to food and the human gut. Because they attack only specific bacteria, researchers are increasingly exploring them as tools for reducing harmful bacteria in humans and animals without disturbing helpful microbes.

That makes them especially interesting at a time of rising antimicrobial resistance. This is when bacteria evolve ways to survive drugs designed to kill them. It’s a global health threat driven in part by the overuse of antibiotics in medicine and agriculture. Unlike broad-spectrum antibiotics, which kill many different kinds of bacteria and can also disrupt helpful gut microbes, research has shown that phages may be able to remove harmful bacteria with less disruption to the wider microbiome.

This has led researchers to investigate phages both as nutraceuticals, dietary supplements intended to promote health, and as feed additives in livestock production. In both cases, the aim is similar: reduce harmful bacteria, support gut health and potentially cut reliance on antibiotics.

Phages work very differently from antibiotics. Rather than killing a broad range of bacteria, each phage typically infects only particular bacterial species or closely related types of bacteria.

When a phage encounters its target bacterium, it attaches to the cell and injects its genetic instructions. The virus then replicates inside the bacterium until the cell bursts. This releases new phage particles that go on to infect other bacteria.

This precision is one reason phages are attracting attention as a possible way to........

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