The microbial world contains trillions of bacteria, alongside powerful, unseen entities that specifically hunt and destroy them. These agents constantly shape the evolution of bacterial life. The history of their discovery involves a curious coincidence: two scientists working independently across Europe during the early 20th century. This dual finding has led to a long-standing historical question about who first observed this phenomenon, which now holds renewed promise for human health.
What Exactly Is a Bacteriophage?
A bacteriophage, often shortened to “phage,” is a type of virus that exclusively infects and replicates within bacterial cells. These viruses are the most abundant biological entities on the planet, characterized by a distinct, tadpole-like structure. The typical phage consists of a polyhedral head (capsid) that encases the genetic material, and an attached tail structure used for attachment and injection.
The phage uses tail fibers to recognize and bind to specific receptor sites on the surface of a bacterium. Once attached, the phage injects its DNA or RNA genome into the host cell’s cytoplasm, initiating a reproductive cycle, most commonly the lytic cycle. This cycle culminates in the destruction of the bacterial cell.
In the lytic cycle, the viral genome hijacks the bacterium’s machinery, forcing it to produce new viral components. These components self-assemble into hundreds of progeny phages. The phages then produce an enzyme, called lysin, that weakens the host cell wall, causing the cell to burst (lyse) and release the new viruses.
The 1915 Observation: Frederick Twort
The first documented observation of this bacteria-destroying phenomenon occurred in 1915 by the English bacteriologist Frederick William Twort. Twort was researching the possibility of cultivating the vaccinia virus, but his cultures were frequently contaminated with micrococci bacteria. He noticed that some bacterial colonies would occasionally undergo a peculiar transformation, becoming transparent and glassy.
Twort discovered that he could filter this “glassy” material, and the resulting filtrate could be transferred to a fresh culture, causing the same destructive effect. He published his findings in The Lancet, describing a transmissible agent that caused a “bacteriolytic agent.” However, he remained uncertain about the agent’s nature, speculating it could be a self-reproducing enzyme, a minute microorganism, or an ultra-microscopic virus.
The outbreak of World War I severely interrupted Twort’s research, preventing him from following up on his observations. His proposal that the agent might be an enzyme secreted by the bacteria, rather than a separate biological entity, limited the immediate recognition of his work. The significance of his 1915 finding was largely overlooked at the time.
The Independent 1917 Discovery: Félix d’Hérelle
Two years later, in 1917, the Franco-Canadian microbiologist Félix d’Hérelle made an independent discovery while working at the Pasteur Institute in Paris. While investigating severe dysentery among French cavalry troops, he observed that a filterable agent in stool samples caused the lysis, or clearing, of Shigella bacteria in his cultures. Unlike Twort, d’Hérelle immediately concluded the agent was an “invisible microbe” parasitic on bacteria, naming it “bacteriophage,” meaning “bacteria eater.”
D’Hérelle quickly recognized the potential for these agents to treat bacterial infections in humans. He began the first therapeutic applications of phages, successfully treating a 12-year-old boy suffering from severe dysentery in 1919. His clear identification, naming, and immediate practical application led to him being widely credited with the discovery and pioneering the field of phage therapy.
Modern Applications of Phage Research
The discovery of antibiotics in the 1940s led to a decline in phage research in the West, but the historical work of Twort and d’Hérelle has recently seen a dramatic resurgence. The global crisis of antimicrobial resistance, where multidrug-resistant (MDR) bacteria are impervious to traditional antibiotics, has forced researchers to seek alternatives.
Phage therapy involves using natural or engineered phages to target specific bacterial pathogens in a patient’s body. Bacteriophages offer a solution because they kill bacteria through a mechanism entirely different from that of antibiotics. A major advantage is their high host specificity, which allows them to target harmful bacteria while leaving beneficial microbiota unharmed.
Modern research is increasingly leveraging synthetic biology to enhance the therapeutic potential of phages. Scientists use tools like CRISPR technology to precisely edit the phage genome, for example, to expand its host range or target more strains of a particular bacterium. They are also engineering phages to carry additional genes that boost their antibacterial power or prevent them from integrating into the host’s DNA, aiming to create customized “designer phages” for personalized treatment against drug-resistant infections.