Bacteriophages: meet the viruses that hunt superbugs

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.

How phages work

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 fight harmful bacteria. Unlike broad-spectrum antibiotics, which can disrupt entire communities of microbes, phages may be able to remove particular harmful bacteria without the same wider effects on the microbiome, according to studies of phage-microbiome interactions and research on antibiotic-associated microbiome disruption.

That raises the possibility that phages could be used not simply to kill bacteria, but to shape communities of microbes in ways that support health. Researchers have explored their potential in food safety, agriculture and human health.

In recent years, researchers and biotechnology companies have begun exploring phages as dietary supplements for humans. The idea is that people could ingest phages to reduce harmful gut bacteria in the hope of restoring balance in the gut microbiome, the community of microbes that lives in the digestive system.

Early findings are encouraging, though still preliminary. For example, one human clinical study found that a commercially available phage product targeting E. coli reduced levels of the bacteria in the gut without causing major disruption to the rest of the microbiome.

Other work has examined phage products designed to support digestive health by targeting bacteria associated with digestive discomfort or dysbiosis, an imbalance in gut microbes. A randomised controlled trial of a phage-based supplement reported improvements in digestive symptoms among participants with mild digestive issues.

This is still an emerging field, and the evidence remains limited. But the results so far suggest phage-based nutraceuticals could eventually form part of diet-based approaches to improving gut health.

There are already signs of commercial interest. In the US, phage products have been approved for certain food safety uses, such as reducing bacterial contamination on foods. Phage-containing supplements are already on sale.

Public acceptance, however, may prove just as important as scientific progress. Because viruses are usually associated with disease, researchers and manufacturers will need to explain clearly why these “good viruses” are different. They occur naturally, they are highly specific and they target bacteria rather than human cells.

Improving animal health through feed additives

Phages may also have an important role to play in livestock production. Farm animals often carry disease-causing bacteria such as Salmonella, Campylobacter and harmful strains of E. coli. These bacteria can harm animal health and contaminate food products. They can contribute to food-borne illness in humans.

Phage-based feed additives are being developed to target these bacteria in livestock. By incorporating phages into feed or drinking water, farmers may be able to reduce harmful bacteria while preserving beneficial microbes that support digestion and the immune system.

Experimental studies have produced promising results. In poultry, phage supplementation has been shown to reduce the presence of Salmonella and Campylobacter, two of the most common causes of food-borne infection worldwide. Research in pigs has also found that phage treatments can reduce harmful E. coli infections, improving gut health and growth.

Phages are also being investigated as alternatives to antibiotic feed additives used to prevent diseases such as liver abscesses – pockets of infection in the liver – in cattle. Because phages replicate only when their target bacteria are present, their effects may naturally taper off once those bacteria are gone, making them a potentially useful way to control infection.

Despite promising research, bacteriophage supplements are not yet widely authorised as feed additives in the UK. Regulators require extensive evidence of safety, stability and effectiveness. Because phages are biological entities that can evolve alongside bacteria, agencies must also consider whether they remain genetically consistent over time and what effects they might have on other microbial communities in the environment.

Even so, regulatory progress is emerging elsewhere. Phage-based food safety products targeting disease-causing bacteria such as Listeria monocytogenes and Salmonella have already been approved in several countries. This includes the US, where they are already being used in food safety applications.

More recently, European regulators authorised the first bacteriophage-based feed additive designed to reduce Salmonella in poultry. That marks an important step towards broader adoption of the technology.

Interest in bacteriophages reflects a wider shift in how microbes are understood in relation to health. If research continues to advance, and regulation keeps pace, phage-based nutraceuticals and feed supplements could become part of a new generation of more targeted ways to shape the microbiome, supporting both human health and more sustainable agriculture.

Tiny though they are, these bacterial viruses may end up playing a significant role in how we manage harmful bacteria.

Manal Mohammed does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.