how-does-phage-therapy-function

Written by Dr. Alain Dublanchet, physician and honorary hospital biologist. — Updated August 29, 2026.

Phage therapy uses natural viruses, bacteriophages, to destroy the bacteria responsible for an infection. Each phage attacks only a single bacterial species: the treatment is custom-prepared from the bacteria sampled from the patient. Practiced without interruption since 1923 at the Eliava Institute in Tbilisi, Georgia, it represents today one of the few options against antibiotic-resistant infections.

The essentials in five points

Principle — viruses that infect only bacteria, without affecting human, animal, or plant cells. Timeline — 7 to 10 days to identify the active phage via a phagogram, then anywhere from a few weeks to 3 months of treatment. Specificity — a phage destroys only one bacterial species: the gut and skin microbiota is preserved. Tolerability — a century of clinical use, with reported side effects that are rare and mild. Where — in Georgia, the only country where the practice has never stopped; the Eliava Institute holds over 6,000 strains there.

What is Phage therapy ?

Phage therapy is a treatment for bacterial infections that uses bacteriophages, natural viruses capable of destroying one specific species of bacteria. It is aimed primarily at patients whose infection no longer responds to antibiotics. Phages infect and destroy bacteria without causing damage to human or animal cells. This is why the therapy is very well tolerated: after a century of clinical use, reported side effects remain rare and mild. The principle is to identify the virus suited to the infection, then apply it to the infected site so that it destroys the bacteria — and only the bacteria. These viruses then multiply on site and continue destroying the identical bacteria they encounter. Phage therapy successfully treats antibiotic-resistant infections, starting with Staphylococcus aureus, but also Pseudomonas aeruginosa, Escherichia coli, and Klebsiella. Details of the conditions concerned are presented on a dedicated page. Before turning to it, consult a specialist doctor and contact a team experienced in the use of phages.

What is phage therapy?

Bacteriophages, or phages, are viruses that infect only bacteria. They are among the most abundant organisms on the planet and pose no danger to human, animal, or plant cells. A phage binds to receptors on the surface of a bacterium, punctures its wall, and enters the cell. Once inside, it multiplies and destroys the bacterium by literally making it burst, in under an hour. The new phages disperse, encounter neighboring bacteria of the same species, and repeat the process. Elimination becomes exponential. Each phage is specific to a single bacterial species. This is what radically distinguishes it from an antibiotic: the infection is eliminated without destroying the beneficial bacteria of the gut, mucous membranes, and skin. Phages are present everywhere — in water, soil, living organisms — where they naturally regulate bacterial populations. Discovered in 1917, they have been studied for over a hundred years and cured millions of patients before the arrival of antibiotics.

Phages vs. antibiotics: what are the differences?

An antibiotic acts on entire families of bacteria, following a standardized protocol that can be applied immediately. A phage targets only one species, and the treatment is prepared from the strain sampled from the patient. Three practical consequences follow: the gut microbiota is preserved instead of being destroyed, side effects remain rare and transient, and resistance never leads to a dead end, since a more active phage can be selected. Methodology, side effects, resistance mechanisms, bacterial targeting, and production conditions are covered point by point on the Comparing Phages and Antibiotics page.

What are the advantages and disadvantages of phage therapy?

The main drawback of phage therapy is its duration: because it is personalized, it takes more time and costs more than antibiotic treatment. The bacterium must first be sampled, cultured, and a phagogram carried out — the search for the most active phage. This process takes 7 to 10 days. Treating a urinary tract infection can then take 2 to 3 months, and longer for multi-resistant osteitis. In return, bacteriophages do not cause serious or lasting side effects, unlike antibiotics. Another decisive advantage: if a bacterium becomes resistant to the phages administered, a more active phage can be selected or adapted from the patient’s own strain. There is therefore never an absolute therapeutic dead end.

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How are phages prepared?

Phages are isolated from environmental samples, then purified, tested, and packaged in a bacteriology laboratory.
A non-sterile sample is collected — river water, wastewater — which always contains numerous bacteria and their associated phages. The sample is homogenized and cleared of solid particles and bacteria. A drop is brought into contact with the bacterium to be fought, cultured for 18 to 24 hours in a broth that becomes cloudy.
After a few hours of incubation, the clearing of the broth signals that the specific phage has recognized “its” bacterium and destroyed it: this is lysis. The operation is repeated from the cleared medium. Adding chloroform eliminates residual bacteria without harming the phages; centrifugation and fine filtration remove the remaining particles.
In this way, a laboratory obtains, within a few days, phages active against a bacterium isolated from a patient. Industrial production of therapeutic phages is far more demanding: purity, concentration, and activity testing, strictly regulated by health authorities as for any medicine.
Artificial intelligence is beginning to be used to shorten this timeframe, by selecting suitable phages from banks of already-characterized strains. This avenue is promising but still under study.

How are phages administered?

The method of administration depends on the site of the infection. A century of practice has validated numerous routes, with no major side effects. Depending on the location, phages are applied locally, injected, nebulized, or infiltrated: mesotherapy for folliculitis, inhalation for a lung condition such as cystic fibrosis. The liquid formulation remains the most common, but tablets, ointments, and incorporation into orthopedic cements also exist. Since phages are sensitive to acidity, oral treatment is preceded by the administration of sodium bicarbonate, to neutralize the gastric fluid. The full process is described on the Phage Therapy Treatment Protocol page.

Who discovered phage therapy?

Phage therapy was invented in 1919 by Félix d’Hérelle, a French-Canadian researcher at the Institut Pasteur, two years after his discovery of bacteriophages.
In 1917, he observed that samples from patients with dysentery, plated on a Petri dish, produced “clear plaques” where the bacteria had disappeared. By transferring these plaques onto other cultures, he obtained the same effect and deduced the presence of a bacteria-killing microbe. He named it bacteriophage, from the Greek phagos, to eat: a bacteria-eater.
The hypothesis was bold. The electron microscope would not appear until the 1940s: it was therefore impossible to observe these organisms at the time. D’Hérelle faced fierce criticism, notably from Nobel laureate Jules Bordet.
In 1919, he isolated these active bacteriophages to administer them to animals, then to patients. To convince his colleagues of their safety, he drank his own preparations himself. He then treated children with shigellosis — then common and often fatal — and cured them. Phage therapy was born, and spread rapidly across Europe, the Americas, and Asia.

Why are phages not used in UK ?

Until 1980, five phage-based medicines were sold in French pharmacies and reimbursed at 75% by Social Security. Their disappearance was not due to a lack of effectiveness, but to the rise of antibiotics and an unsuitable economic model. After the Second World War, antibiotics — simpler to study, produce, and prescribe — took over. The production and sale of phages gradually ceased in France and the West. Antibiotic resistance was not yet an issue at the time; phages fell into disuse, unnoticed. Today, the rapid rise of antibiotic resistance is bringing this solution back to the forefront. One obstacle remains: phages were not invented but collected from nature. They are therefore not patentable, which has long discouraged the pharmaceutical industry. The regulatory framework remains complex.

Why is phage therapy authorized in Georgia?

Georgia has never banned phage therapy: it has been practiced there without interruption since 1923. The dedicated research institute was founded that year in Tbilisi by the Georgian bacteriologist Giorgi Eliava. He had met Félix d’Hérelle at the Institut Pasteur in Paris between 1919 and 1921 and had invited him to work in his laboratory. D’Hérelle traveled to Tbilisi in 1933 and 1934, then worked there for about eighteen months starting in 1934, where he wrote The Bacteriophage and the Phenomenon of Recovery (1935). The institute today bears its founder’s name: the Eliava Institute. During the Soviet era, with antibiotics less accessible than in the West, phages continued to be studied, produced, and prescribed. This continuity has given Georgia over a hundred years of uninterrupted practice and one of the largest phage collections in the world, estimated at over 6,000 strains. Phage therapy is still taught today in Georgian medical schools, which is not the case anywhere in the West. Georgian doctors therefore have know-how, clinical experience, and authorizations that do not exist elsewhere. The remaining question is where to get treated.

On this site you will find everything you need to understand phage therapy and assess whether it fits your situation, starting with testimonials from patients already treated. To go further, you can request a personalized medical opinion or check the cost of phage therapy in Georgia.

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