Scientists are developing bacteriophages—viruses that infect and destroy bacteria—as a possible treatment for infections that no longer respond to traditional antibiotics. An international group led by the German Society for Infectious Diseases (DGI) has now published the first internationally harmonized clinical guidelines for personalized phage therapy, outlining more than 60 recommendations for selecting, testing, manufacturing, administering and monitoring these highly targeted treatments.
Creating standards for personalized phage therapy
The effort involved 18 international experts, including representatives from 20 professional bodies, regulatory authorities and two patient advocacy groups. Their recommendations also cover laboratory infrastructure, quality control, treatment documentation and priorities for future research.
The consensus statement was published in Nature Medicine. Until now, doctors and researchers have lacked a unified international framework for many of the procedures and quality standards needed to use phages in medical care.
How bacteria-killing viruses could address antibiotic resistance
Antibiotic resistance is making bacterial infections increasingly difficult to treat worldwide. As some bacteria develop defenses against commonly used drugs, doctors may have few effective options.
One potential alternative is bacteriophage therapy. Bacteriophages, commonly called phages, are viruses that naturally infect and destroy bacteria. Unlike many antibiotics, which act against a broad range of bacteria, phages typically target a specific bacterial species or even an individual strain.
This precision makes phage therapy promising, but it also creates challenges. A phage that kills one bacterial strain may have little or no effect on another. Before treatment begins, specialists must therefore determine whether a particular phage can attack the bacteria causing a patient’s infection.
Personalized phage therapy may be considered when established treatments have failed, are unavailable or cannot be used safely. Previous studies suggest that properly manufactured and administered phages generally have a good safety profile. However, controlled clinical trials have not yet produced enough evidence to establish how reliably the treatment works.
For that reason, the new guidelines do not recommend phage therapy as a routine treatment for bacterial infections. Instead, they call for careful evaluation of each patient and use of the approach only when the circumstances warrant it.
Early results show promise against difficult infections
Although important questions remain, early clinical experience suggests that phage therapy may help some patients with refractory infections.
In a Belgian case series involving 100 people who received phage treatment, 77 percent experienced an improvement in their clinical condition. In 61% of cases, tests could no longer detect the targeted bacteria.
These findings are encouraging, particularly for infections that are difficult to control with existing drugs. However, observational studies cannot establish whether phages caused the improvement or determine how effective the treatment is under controlled clinical conditions.
Larger, carefully designed studies will be needed to clarify phage therapy’s effectiveness and identify which patients are most likely to benefit.
Matching the right phage to each infection
A central challenge in personalized phage therapy is finding the right virus for each patient.
Because phages are highly selective, laboratories must test whether a candidate virus can kill the specific bacterial strain involved in an infection. This process, known as a “phage match,” should be completed as quickly as possible before treatment begins.
Timing matters because bacteria can change their susceptibility to phages during an infection. When multiple bacterial pathogens are present, specialists should test for all relevant microorganisms rather than focusing on only one.
The guidelines recommend that treatment decisions involve a team including the patient’s physician, a clinical microbiologist and a recognized phage expert. This collaborative approach is intended to help clinicians select suitable phages and determine whether treatment is justified.
The recommendations also establish expectations for cooperation among laboratories, phage manufacturing facilities, pharmacies and clinical teams. Consistent testing methods and regular proficiency assessments can help ensure that results from different facilities are reliable and comparable.
Another priority is the detailed documentation of every treatment. The guidelines call for cases to be systematically recorded and registered so researchers can compare clinical experiences, identify problems and investigate unanswered questions.
“Standardization of quality standards and identification of infrastructure requirements for the production of phages for personalized use are essential elements of guidelines and important prerequisites for reliable treatment,” said Dr. Annika Klassen.
Klaassen, a researcher at the German Research Center for Infectious Diseases (DZIF), played a leading role in developing the recommendations. She also leads the Translational Bacteriophage Research Group at Cologne University Hospital.
Other key contributors include PD Dr. Sylvia Wursl, Professor Maria Wereschild and Dr. Simone Lieberknecht-Joy from Goethe University Frankfurt. Wereschild is deputy coordinator of the DZIF research field Healthcare-Associated Infectious Diseases, and Klassen, Wursl and Lieberknecht-Joy are also involved in the research.
German hospitals begin using personalized phage therapy
The potential of the approach is already being investigated in clinical practice.
“This guideline provides physicians, pharmacists, and regulators with a common framework to safely and responsibly incorporate phage therapy into clinical practice,” said the guideline’s lead author, Dr. PD Wursl.
At Frankfurt University Medical Center, Wursl is overseeing the development of the facilities and procedures needed to offer phage therapy in accordance with the new recommendations.
The medical center reports that, since February 2026, it has successfully treated 10 patients through its guideline-based phage therapy program. Each treatment uses individually selected viruses to target the bacteria causing the patient’s infection.
The pathogens treated include Pseudomonas aeruginosa and Staphylococcus aureus, two bacterial species associated with infections that can be particularly difficult to manage, especially when antibiotic resistance is involved.
The delivery method depends on the infection and the patient’s medical needs. Treatment may involve intravenous administration, inhalation, a nasal spray or application with sterile hydrogel.
These options show how personalized phage therapy can be adapted to specific clinical situations rather than relying on a single method of treatment.
International standards may shape the future of phage therapy
Building a reliable phage therapy system requires coordination across multiple medical and scientific disciplines.
The guidelines identify PhageNET DZIF, a network founded and coordinated by Claßen, as an important platform for exchanging scientific knowledge and clinical experience.
By bringing together expertise in microbiology, clinical medicine, pharmacy, manufacturing and regulation, the new framework aims to help specialists understand both the potential and the limitations of personalized phage therapy.
The recommendations were developed through a structured consensus process under the AWMF (Association of German Scientific and Medical Societies). They are valid from January 5, 2026, to June 29, 2030. The responsible committee will review them annually to determine whether they need to be renewed.
Phage therapy still requires stronger evidence from controlled clinical trials, but the international standards provide a clearer path for its responsible development. For patients with infections that cannot be adequately treated with traditional antibiotics, bacteria-killing viruses could eventually become another treatment option.
Source: www.sciencedaily.com
