Scientists are developing bacteriophages—viruses that infect and destroy bacteria—as a potential treatment for dangerous infections that no longer respond to conventional antibiotics. An international expert group led by the German Society for Infectious Diseases (DGI) has now published the first internationally harmonized clinical guidelines for personalized phage therapy, establishing more than 60 recommendations for selecting, testing, manufacturing, administering and monitoring these highly targeted treatments.
Guidelines aim to make phage therapy safer
The initiative involved 18 international experts, representatives from 20 professional bodies and 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 natural medicine. Until now, doctors and researchers have lacked a unified international framework for many of the procedures and quality standards involved in using phages medically.
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, physicians can be left with few effective options.
Bacteriophages, commonly called phages, offer one possible alternative. These viruses naturally infect and destroy bacteria. Unlike many antibiotics, which affect a broad range of microorganisms, phages typically target a particular bacterial species or even a specific strain.
This precision is one of the main advantages of phage therapy, but it also creates a practical challenge. A phage that kills one bacterial strain may have little or no effect on another. Before treatment begins, specialists must therefore determine whether a candidate 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 clinical circumstances justify it.
Early clinical results are encouraging but limited
Although important questions remain, early clinical experience suggests that phage therapy may help some people with refractory infections.
In a Belgian case series of 100 people who received phage treatment, 77 percent experienced an improvement in their clinical condition. In 61 percent of cases, tests could no longer detect the treated bacterium.
These findings are encouraging, particularly for infections that are difficult to control with existing drugs. However, observational studies cannot show whether phages caused the improvement or determine how effective the treatment would be in controlled clinical trials.
Larger, carefully designed studies will be needed to clarify the effectiveness of phage therapy 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 a virus that can attack the bacteria infecting a particular patient.
Because phages are highly selective, laboratories must test whether a candidate virus can kill the specific bacterial strain involved. This process, known as a “phage match,” should be completed as quickly as possible before treatment starts.
Timing is important because bacteria can change their susceptibility to phages during an infection. When several bacterial pathogens are present, specialists should test all relevant microorganisms rather than focus 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 decide whether treatment is warranted.
The recommendations also define 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 detailed treatment documentation. The guidelines call for cases to be systematically recorded and registered so that 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, while Klassen, Wursl and Lieberknecht-Joy are also involved in the research.
German hospitals begin using personalized phage therapy
The potential of phage therapy 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 facilities and procedures needed to provide 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. Phages may be administered intravenously, by inhalation or nasal spray, or through application with sterile hydrogel.
These options illustrate how personalized phage therapy can be adapted to specific clinical situations rather than relying on a single method of administration.
International standards could shape future research
Building a reliable phage therapy system requires coordination across multiple medical and scientific disciplines.
The guidelines highlight 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 framework aims to help specialists assess 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 require renewal.
Phage therapy still needs stronger evidence from controlled clinical trials, but the new 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 valuable treatment option.
Source: www.sciencedaily.com