At this time of year, it starts to feel like everyone is getting sick, and it’s hard not to resent the germs responsible. If a common cold or flu is keeping you home from work, the cause is likely a virus.
Viruses have developed an infamous reputation, especially in recent years. However, just like how we sometimes talk about our ‘good bacteria’ and ‘bad bacteria’, there can be some ‘good’ viruses too. Viruses are actually a pretty vital part of our microbiome; they help strengthen our immune system and can even deliver vaccines or help identify illnesses. (Dutchen, 2023)
Viruses infect every living creature, from plants down to the microscopic. So, if we get sick from viral infections, what happens when they infect bacteria? Why does it matter?
Viruses could help us solve one of our most urgent and pressing problems, antibiotic resistance.
What is antibiotic resistance? Antibiotic resistance happens when a bacterial strain evolves to survive exposure to a drug. This happens naturally through genetic changes in the bacteria as they multiply, mutate or share DNA between cells. (WHO, 2024)
It is estimated that bacterial antimicrobial resistance was directly responsible for 1.27 million deaths and contributed to 4.95 million deaths in 2019. (WHO, 2023). The development of antimicrobial resistance is being accelerated by human activity including misuse and overuse of antibiotics. It means that many of our antibiotic treatments may stop working. All over the world, researchers are looking into alternative ways to kill bacteria with increasing urgency.
Structure of a Bacteriophage
Bacteriophage treatment is one of these alternatives.
Bacteriophages, or phages, are viruses that only infect bacteria cells. These alien looking microbes are bacteria's natural predators; they were the first viruses to be discovered and are found everywhere on Earth. (Kasman & Porter, 2022)
Phage therapy works by using phages to kill bacteria. To understand how this works, it helps to understand phage lifecycles. On its own, a virus cannot use energy, create energy, move, or multiply. To replicate, they hijack the machinery and energy inside the cell of a host, to produce their own viral parts.
When bacteriophages complete their lysogenic lifecycle as below, they destroy the bacterial cell as the new viruses exit the cell. The new viruses then infect more bacterial cells, and repeat the process of enter, hijack, replicate, destroy, wiping out bacterial populations quickly and effectively. (Kasman & Porter, 2022) Humans can harness this natural cycle to kill bacterial infections.
This diagram shows the (lysogenetic) lifecycle of a phage:
Phage therapy has many advantages.
Because the viruses multiply and mutate at a very fast rate, they can often keep up with their bacterial targets evolution. As fast as a bacterium evolves the power to resist, a virus can evolve the power to overcome it. So unlike antibiotics, resistance is responded to in real time by the virus. (Borin et al., 2021)
Phage therapy is also more targeted than antibiotics, as phages usually only infect one species of target bacteria. (Kasman & Porter, 2022) Antibiotics do not target specific bacteria and can kill a lot of good bacteria in your body in the process of curing an infection, causing unpleasant side effects. (WHO, 2025)
Phages can target specific bacteria because they are so good at identifying different types of cells. Almost every cell that exists has special proteins on its surface. These proteins help cells perform essential tasks, and different proteins exist on different types of cells. Proteins on bacteria cell surfaces are very different from the ones on human cells, plant cells, animal cells, or even cells in different parts of the body.
Viruses have proteins on their surface too, these proteins are designed to recognise and clip onto the proteins on their preferred host cell, like a puzzle piece.
This means viruses are highly specific and only infect a cell if it has the exact ‘puzzle piece’ match.
Some countries have been using phage therapy for over 100 years...
While Western countries, like America, decided to invest in the development of new kinds of antibiotics, Eastern European countries, especially members of the former Soviet Union, chose to develop phage treatments.
There are a few reasons for this, and a major social factor was the occurrence of WWII, and the Cold War. Many western scientists avoided the use of phage therapy as it was so strongly associated with the Soviet Union, and scientific collaboration wasn't exactly encouraged at this time. (Medlow, 2025)
Phage therapy does have other challenges that may have impacted the choice to abandon development.
One of these challenges was that, at the time that phages were discovered, nobody really knew how they worked. Scientists didn’t realise how specific viruses are to their hosts. The viral protein needs to match the protein on the bacteria’s surface exactly. Which means that for any infection to be treated, you need to find the exact phage matching the exact bacteria causing the infection. Without understanding this, it could have seemed like phages were simply unreliable treatments. (Barron, 2026)
Solutions such as ‘phage cocktails’, mixtures of many different phages that target many bacteria at once, have been developed to combat this (and yes, you can drink them!).
A viral comeback...
Phage therapy is now having a resurgence in western medicine and has been used to combat antibiotic resistant infections in people with success. More research needs to be completed on the safety and effectiveness of these treatments before they can become widely available. However, there is potential for phages to become one of our biggest allies in the fight against antimicrobial resistance. (WHO, 2025)
Who knows, next time you're suffering a stubborn bacterial infection, maybe you'll be swapping out your martini for a phage cocktail!
Jai Tarn
References
Barron, M. (2026, February 24). Phage therapy: Past, present and future. American Society for Microbiology. https://asm.org/articles/2022/august/phage-therapy-past,-present-and-future
Borin, J. M., Avrani, S., Barrick, J. E., Petrie, K. L., & Meyer, J. R. (2021, June 3). Coevolutionary phage training leads to greater bacterial suppression and delays the evolution of phage resistance. Proceedings of the National Academy of Sciences, 118(23), e2104592118. https://doi.org/10.1073/pnas.2104592118
Dutchen, S. (2022). The good that viruses do. Harvard Medicine Magazine. https://magazine.hms.harvard.edu/articles/good-viruses-do
Kasman, L. M., & Porter, L. D. (2022, September 26). Bacteriophages. In StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK493185/
Medlow, A. (2025, November 19). The politics behind the global divide in bacteriophage therapy. The Microbiologist. https://www.the-microbiologist.com/opinion/the-politics-behind-the-global-divide-in-bacteriophage-therapy/7180.article
World Health Organization. (2023, November 21). Antimicrobial resistance. https://www.who.int/news-room/fact-sheets/detail/antimicrobial-resistance
World Health Organization: Regional Office for Europe. (2024, September 19). Antimicrobial resistance. https://www.who.int/europe/news-room/fact-sheets/item/antimicrobial-resistance
World Health Organization: Regional Office for Europe. (2025, February 17). Bacteriophages and their use in combating antimicrobial resistance. https://www.who.int/europe/news-room/fact-sheets/item/bacteriophages-and-their-use-in-combating-antimicrobial-resistance