You might have seen the word ‘bacteriophage’ appear more often in the media, news articles, and scientific publications in the recent years. But what exactly are bacteriophages? What do they do, and how can they be used in healthcare? This blog starts a series in which we take a closer look at the bacteriophage and its possible applications in healthcare, screening and diagnostics.
What are bacteriophages?
Bacteriophages, or phages for short, are one of the most numerous microorganisms on the planet. Some estimate that the number of phage particles on Earth is 1031 – a nonillion, which roughly translates to around a trillion phages for every grain of sand in the world.
Phages are virus-like organisms that are present everywhere – in water, soil, plants and even our skin and metabolism. Compared to other organisms they can survive in extreme environments and withstand fairly high and low temperatures. Bacteriophages have a crucial role in regulating the world’s bacterial populations. Some studies estimate that they kill anywhere between 15–40% of the bacteria in our oceans every day.
The discovery of phages
Bacteriophages were first discovered and used successfully in treatment already in the beginning of the 20th century. William Twort first observed them in 1915, after which Felix d’Herelle realized their bacteria-killing potential in 1917.
However, the research and development of bacteriophages was quickly overshadowed by the discovery of penicillin. While antibiotics reliably killed all bacteria making their administration extremely easy, the use and research into phages, which required more in depth skills, declined significantly. For several decades phages were left on the back burner as antibiotics seemed to be the ultimate solution to all infections.
But luckily, the study of phages did not die out completely, and their study and development continued throughout the 20th century in a few dedicated research institutions and universities around the world.
How phages operate
Because bacteriophages are a type of virus, like other viruses they don’t have the ability to replicate on their own. To reproduce, they need a host cell. And bacteriophages are very specific about their host cell. Through millions of years phages have evolved and specialized to survive by exclusively infecting and killing bacterial cells without harming the surrounding human or animal cells. But the phage’s specificity does not end there – specific phages are programmed to only kill specific species of bacteria, like predators in nature only hunting one type of prey.
When phages find their bacterial host cell they attach to it and start using the host cell’s nutrients to multiply and replicate themselves inside the host. And when all the nutrients in the host cell are used, the new phages make their exit. The new phages produce an enzyme called endolysin that destroys the host bacteria’s walls, killing the host from the inside and releasing the new phages. Then, the newly released phages start to look for their own host cell to infect, and the process starts again from the beginning.
A growing need for alternative solutions
In the last few decades antibiotic-resistant bacteria have become an ever more serious global threat. Some researchers and scientists have even proclaimed the era of antibiotics to be over as doctors and hospitals struggle with new forms of bacteria that cannot be defeated with conventional means.
According to WHO, antibiotic resistance is one of the biggest threats in health care globally. It’s estimated that at least 700,000 people die annually because of drug-resistant diseases, and the number will continue to rise if no action is taken.
Through the years phages have been sporadically used to treat individual patients around the world, often with success. They also have other potential applications in screening and diagnostics. The interest in phages and phages has picked up significantly during the last 20 years, and the next big discoveries are most likely just around the corner. In our next phage-related blog post, we will discuss the use of phages in healthcare in more detail.
Keen EC. A century of phage research: bacteriophages and the shaping of modern biology. Bioessays. 2015;37(1):6-9. doi:10.1002/bies.201400152
Clokie MR, Millard AD, Letarov AV, Heaphy S. Phages in nature. Bacteriophage. 2011;1(1):31-45. doi:10.4161/bact.1.1.14942
Fernando L. Gordillo Altamirano, Jeremy J. Barr. Phage Therapy in the Postantibiotic Era. Clinical Microbiology Reviews. 2019; 32 (2). doi: 10.1128/CMR.00066-18