Common standards for the use of phages against hard-to-treat infections
International group of experts develops more than 60 recommendations – DZIF scientists play key role in developing the guideline
Holes in the bacterial colony on an agar plate—these are the first indications of a new bacteriophage.
An international working group led by the German Society for Infectious Diseases (DGI) has developed a guideline for personalized phage therapy. Twenty professional organizations, 18 international experts, including representatives from regulatory agencies, and two patient advocacy organizations were involved. The guideline includes more than 60 practice-oriented recommendations on the selection and testing of suitable phages, infrastructure, manufacturing and quality control, application, monitoring, and documentation, as well as future research questions. The consensus statement will be published on September 21, 2026, in the journal Nature Medicine.
The guideline provides the first internationally coordinated framework for the clinical application of personalized phage therapies. Until now, there have been no uniform recommendations for key steps in treatment or quality standards for the use of phages as therapeutics.
A treatment option for difficult-to-treat infections
Antibiotic-resistant bacteria complicate the treatment of infections worldwide. Bacteriophages—or phages for short—are viruses that can specifically infect and kill bacteria. Unlike many antibiotics, they are usually only effective against certain bacterial species or individual strains. Before treatment, it must therefore be determined whether a suitable phage is effective against the specific pathogen.
Personalized phage therapy may be particularly considered when established treatment options are ineffective, unavailable, or unsuitable. Clinical research to date indicates a favorable safety profile when phages are manufactured and administered according to appropriate quality standards. However, their efficacy has not yet been sufficiently demonstrated by controlled clinical trials. The new guideline therefore regards phage therapy as a treatment option to be evaluated on a case-by-case basis and not as a generally available standard treatment.
Observational data provide initial indications of potential treatment success: In a Belgian case series involving 100 treated individuals, the clinical condition improved in 77 percent; in 61 percent of cases, the targeted bacteria were subsequently undetectable. However, such observational data cannot replace controlled clinical trials.
Transmission electron micrograph of a bacteriophage targeting Pseudomonas aeruginosa.
Standardized procedures for individualized therapy
Since phages react very specifically to their bacterial hosts, a suitable phage must be identified for each treatment case, and its efficacy against the specific bacterial strain must be verified. The guideline recommends evaluating each case through an interdisciplinary approach involving the treating physicians, the clinical microbiology department, and recognized phage experts. Before starting treatment, it should be determined as soon as possible whether the phage is effective against the specific bacterial strain—the so-called “phage match.” This is important because bacterial susceptibility can change over the course of an infection. In cases of infections caused by multiple pathogens, all relevant bacteria should be tested.
The guideline also describes collaboration between laboratories, phage production facilities, pharmacies, and clinical teams. Standardized testing procedures and regular proficiency testing are intended to improve the quality and comparability of results. Treatment cases are also to be systematically documented and entered into registries to evaluate experiences from clinical use and address ongoing research questions in a more targeted manner.
“The standardization of quality criteria for the production of phages for personalized use, as well as the identification of infrastructural requirements, are essential components of the guideline and important prerequisites for reliable treatments,” says Dr. Annika Claßen. The DZIF researcher played a leading role in developing the guideline. She heads the “Translational Bacteriophage Research Group” at the University Hospital Cologne.
Other leading researchers involved in the guideline include PD Dr. Silvia Würstle, Prof. Maria Vehreschild, and Dr. Simone Lieberknecht-Jouy from Goethe University Frankfurt. Prof. Vehreschild is the deputy coordinator of the DZIF research area “Healthcare-Associated Infections,” in which Dr. Claßen, PD Dr. Würstle and Dr. Lieberknecht-Jouy also work as researchers.
Implementation into clinical practice
“The guideline provides physicians, pharmacists, and regulatory authorities with a common framework for safely and responsibly incorporating phage therapy into clinical practice,” says PD Dr. Würstle, the corresponding author of the guideline. At Frankfurt University Medical Center, she is responsible for establishing the infrastructure for phage therapy in accordance with the guideline.
Developments at Frankfurt University Medical Center demonstrate how this approach can be implemented in clinical practice: Since February 2026, ten patients have been successfully treated there as part of a phage therapy program that adheres to the clinical guideline. This treatment uses individually selected phages to combat various pathogens, including Pseudomonas aeruginosa and Staphylococcus aureus. Depending on the clinical situation, the phages can be administered intravenously, by inhalation, or as a nasal spray. They can also be applied as a sterile hydrogel.
The guideline cites the DZIF network PhageNET DZIF – established and coordinated by Dr. Claßen – as a platform for scientific and clinical exchange on phage therapy. The guideline brings together expertise from the fields of microbiology, clinical medicine, pharmacy, manufacturing, and regulation. It is intended to help specialists better assess the prerequisites and limitations of individualized phage therapy.
The guideline was developed through a consensus-based process within the structured framework of the AWMF (Association of the Scientific Medical Societies in Germany). It is valid from January 5, 2026, through June 29, 2030. The responsible committee is to review annually whether an update is necessary.
