Hygiene Prize of the Rudolf Schülke Foundation 2022 New biofilm model to determine the effectiveness of antimicrobial substances against wound biofilm

Even though wound healing disorders and chronic wounds are part of everyday life for many people, this topic is not very well known among the general population, which is not affected, and also receives little attention in the press.

Based on different internistic, dermatological and immunological diseases, about 2% of the population in western countries suffer from chronic wounds, i.e. wounds that have not healed within six weeks despite adequate treatment. Biofilms are a frequent trigger for disturbances in the healing process (Figure 1). They can form on the wound within 24 to 48 hours. Biofilms are complex networked communities of bacteria, fungi or other microorganisms that, together with proteins and sugars, form a gel-like matrix. This can adhere to inanimate surfaces, such as the inner wall of shower hoses, as well as to vital tissue of a wound. There, biofilms trigger chronic inflammation, which can also damage healthy tissue structures and severely impede wound healing.

A meta-analysis from 2016 showed [2] that about 80% of chronic wounds are populated with pathogenic microorganisms in a biofilm. The removal of the bacterial load and the biofilm of a chronic wound, i.e. the elimination of chronic inflammation, is the first step in local therapy, according to Prof. Stürmer. Only when this is successful can positive influences such as growth factors, MMP blockers or even autologous stem cells effectively intervene in the stagnating wound healing. However, the slimy matrix of the biofilm makes it difficult for antiseptic (and antibiotic) agents to reach the microorganisms and eradicate them. Wound irrigation solutions that kill planktonic, i.e. "free-swimming" bacteria, usually do not achieve the same effect in biofilm constructs. In the S3 guideline on local therapy of chronic wounds of the German Society for Wound Healing (DGfW), which is currently being amended, the quality of evidence for the use of antiseptic solutions for wound cleansing in pathogen-induced inflammation is assessed as low [3]. Reliable measures to sustainably control recurrent bacterial colonisation and the formation of new biofilm are still lacking. Wound debridement is currently in the foreground as the means of choice.

The starting point for Prof. Stürmer's research was the observation that the human biofilm model hpBIOM (individual human donor), which has so far been used to evaluate the efficacy of wound antiseptics in her working group, is reserved for special laboratories because a positive ethical vote for the respective user and the consent of the respective blood donor would always be required. Thus, hpBIOM is not suitable for a comprehensive, standardised efficacy testing of antimicrobial substances.

In the publication [1], which has now been awarded the Hygiene Prize, the team of authors tested the efficacy of various antiseptics in the presence of a wound biofilm using three different biofilm models. Two 3D biofilm models, one based on human plasma with immune cells (lhBIOM) and one based on sheep blood (sbBIOM) with hpBIOM were compared with regard to the microscopic structure of the biofilm (scanning electron microscopy; SEM) and their bacterial tolerance to wound irrigation solutions based on octenidine hydrochloride and sodium hypochlorite/hypochlorous acid, respectively. The animal "sheep" was chosen because sheep erythrocytes are already used in DIN EN 13727 as an increased challenge in determining the efficiency of an antimicrobial product. S. aureus and P. aeruginosa were used as test organisms.

On the one hand, it was shown that the biofilm model based on sheep's blood, which is much easier to use over a wide area, is structurally comparable to the human models in terms of its effect profile and is therefore very well suited as a practical model for the approval of (new) antimicrobial agents by accredited laboratories.

On the other hand, in a direct comparison between a wound irrigation solution containing sodium hypochlorite and hypochlorous acid and Octenisept^® (medicinally active ingredients: octenidine hydrochloride and phenoxyethanol), it was clearly demonstrated that the hypochlorous wound irrigation solution achieved only very low to no efficacy in the biofilm models. Octenisept^®, on the other hand, was effective in all three biofilm models.

In the biofilm model based on sheep's blood, Octenisept^® was able, for example, to reduce the bacterial count of P. aeruginosa, the more resistant of the two test organisms, at an initial bacterial count of 1.5x106 CFU/model by 2 log10-levels after 24 h, by 7 log10-levels after 48 h, and completely eliminated after 72 h. The results of the study were also positive. In addition, clear fissures in the biofilm could be detected in the scanning electron microscope after administration of Octenisept^®. Prof. Stürmer assumes that the additives in Octenisept^® play a significant role in this, as some have the potential to cleave proteins or sugars in the biofilm.

Prof. Dr. med. Ewa Stürmer is a specialist in surgery, orthopaedics and trauma surgery and a recognised qualified expert in the field of translational wound research. Since 2020, she has been senior physician and head of the Comprehensive Wound Center of the Clinic and Polyclinic for Vascular Medicine of the University Heart and Vascular Center of the University Medical Center Hamburg-Eppendorf.

Her translational and clinical research focus has been on "wound biofilm" for many years. She is not only interested in developing new therapy options using a human biofilm model based on blood plasma, but also in analysing the high tolerance of the biofilm against external "forces" through interbacterial communications in cellular and molecular biology. It is important to her, says Prof. Stürmer, that transnational research is more strongly perceived. This research, she emphasises, is an important link between clinical research and basic research. She does not lose sight of everyday clinical life and "researches" close to patients, i.e. focuses on what can be of use to users. This is why translational research is often caught between two stools and receives less funding than basic research on the one hand and clinical research on the other.

In his laudatory speech for the award winner, Priv.-Doz. Dr. med. Albert Pitten, Institute for Hospital Hygiene and Infection Control Gießen and Deputy Chairman of the Rudolf Schülke Foundation, praised the originality, methodology and relevance of the study as well as the extraordinary scientific commitment of the award winner, e.g. in her supervision of already more than 70 medical, dental and pharmaceutical doctoral students. The development of the biofilm model based on sheep's blood, which is close to the reality of the human wound biofilm in vital tissue, will make it possible in future to test and evaluate the efficacy of antimicrobial substances for use on chronic wounds that are usually colonised with biofilm in a standardised manner.

The Hygiene Award with the certificate was presented to Prof. Stürmer and Prof. Smeets, co-author and Deputy Director of the Clinic and Polyclinic for Oral and Maxillofacial Surgery at the University Medical Center Hamburg-Eppendorf, on 20 May 2022 in Hamburg as part of the ceremony marking the 50th anniversary of the Rudolf Schülke Foundation [Figure 2].

The Hygiene Prize, endowed with 15,000 €, is not only financially attractive, but also supports scientists in applying for important positions such as chairs at German universities. In the excellent lecture by Prof. Stürmer entitled "Pitfalls in antimicrobial efficacy profiles" it became immediately clear why this work is worthy of the prize. In her summary, Prof. Stürmer also pointed out that the development of the sheep's blood biofilm model will in future make it possible to dispense with animal experiments for "anti-biofilm" questions.

Every two years, the Rudolf Schülke Foundation organises a symposium in Hamburg to which scientists are invited to discuss important hygiene issues. This year's topic was antisepsis. This was also the topic of the Foundation's first working meeting in 1972. Today, it is particularly important to answer questions about antiseptic stewardship and to promote more epidemiological studies with reliable results for different active substances for the various areas of application.

The awarding of the Hygiene Prize and the Hygieia Medal took place following the working meeting as part of a ceremony marking the Foundation's 50th anniversary. The Hygieia Medal was awarded this year to Prof. Dr. med. Thomas Mertens, virologist and Chairman of the Permanent Vaccination Commission (STIKO) at the Robert Koch Institute.

The company Schülke & Mayr founded the Rudolf Schülke Foundation with the aim of promoting hygiene and microbiology with a focus on the prevention and control of communicable diseases in the service of public health. In the meantime, the objectives and scope have expanded, adding a focus on global health and patient safety. The aim is also to promote a global dialogue between representatives from different fields of science and research and to cooperate with universities.

More information on the Rudolf Schülke Foundation, the 50th anniversary as well as the Hygiene Prize and the Hygieia Medal on the Foundation's website www.rudolf-schuelke-stiftung.de
Every two years, the Rudolf Schülke Foundation organises a symposium in Hamburg to which scientists are invited to discuss important hygiene issues. This year's topic was antisepsis. This was also the topic of the Foundation's first working meeting in 1972. Today, it is particularly important to answer questions about antiseptic stewardship and to promote more epidemiological studies with reliable results for different active substances for the various areas of application.

The awarding of the Hygiene Prize and the Hygieia Medal took place following the working meeting as part of a ceremony marking the Foundation's 50th anniversary. The Hygieia Medal was awarded this year to Prof. Dr. med. Thomas Mertens, virologist and Chairman of the Permanent Vaccination Commission (STIKO) at the Robert Koch Institute.

The company Schülke & Mayr founded the Rudolf Schülke Foundation with the aim of promoting hygiene and microbiology with a focus on the prevention and control of communicable diseases in the service of public health. In the meantime, the objectives and scope have expanded, adding a focus on global health and patient safety. The aim is also to promote a global dialogue between representatives from different fields of science and research and to cooperate with universities.

More information on the Rudolf Schülke Foundation, the 50th anniversary as well as the Hygiene Prize and the Hygieia Medal on the Foundation's website www.rudolf-schuelke-stiftung.de