Engineered Phage Endolysin Eliminates _Gardnerella_ Biofilm without Damaging Beneficial Bacteria in Bacterial Vaginosis Ex Vivo  
[PERSON]  
1 PhagoMed Biopharma GmbH, Vienna Biocenter, 1110 Wien, Austria; [EMAIL_ADDRESS] (C.L. ); [EMAIL_ADDRESS] (L.T. ); [EMAIL_ADDRESS] (V.); [EMAIL_ADDRESS] (T.S. ); [EMAIL_ADDRESS] (A.M.)  
[PERSON]  
2 Laboratory Bacteriology Research, Department of Diagnostic Sciences, Faculty of Medicine & Health Sciences, Ghent University, Flanders, 9000 Gent, Belgium; [PERSON] (A.L. ); [PERSON]] (L.V.S. ); [PERSON].V.) Muhammad  
in the normal, healthy microbiome of the vagina that results mostly in discharge, odor, and irritation. BV is associated with an increased risk of preterm delivery and low birthweight [3; 4], infertility and early spontaneous abortion [5; 6; 7], and it is also a high risk factor for contracting sexually transmitted diseases, including HIV [8; 9]. Besides these potentially severe physiological consequences, frequently recurring and strongly symptomatic BV can have a huge negative impact on some women's quality of life and psychological wellbeing. The healthy vaginal microbiome is characterized by a low diversity and uniform colonization by a few species of _Lactobacillus_[10]. In BV, the imbalance in the vaginal microbiome is represented predominantly by the loss of beneficial lactobacilli and overgrowth of bacteria such as _Gardnerella_, _Prevotella_, _Atopobium_, _Sneathia_[11], and _Lactobacillus iners_[12]. The current model of the etiology of BV focuses on the importance of _Gardnerella_ species. It postulates that virulent strains of _Gardnerella_ form an adherent biofilm on the vaginal epithelium in which other species can proliferate, resulting in a polymorphic biofilm [13; 14; 15; 16; 17]. This adherent biofilm is only weakly affected by the innate immune response [18], and the interplay with the host immune system is only partially understood [19]. BV development may be triggered by sexual transmission of a mix of bacteria including _Gardnerella_, which can adhere to epithelial cells in the presence of lactobacilli. It has been suggested that, unlike strictly anaerobic bacteria associated with BV, _Gardnerella_, a facultative anaerb, can tolerate the high redox potential created by the Lactobacillus-dominated healthy vaginal microbiome [15; 20; 21]. The metabolism of _Gardnerella_ spp., in turn, results in a local increase in pH and decrease in redox potential, favoring the growth of iron-dependent anaerbes [10] and suppression of lactobacilli [22]. Recently, the species previously known as _Gardnerella vaginalis_ was shown to comprise at least 13 different species of which 4 were named [23]. Clinical studies indicated that various _Gardnerella_ species may contribute differently to the pathogenesis of BV. A higher abundance of _G. vaginalis_ and _G. swidsinskii_ was found to be related with vaginal symptoms of abnormal odor and discharge and the relative abundances of _G. vaginalis_, _G. swidsinskii_, and _G. piotiti_ but not _G. leopoldii_ were strongly associated with the BV microbiome [24; 25]. The therapies used currently to treat BV are broad-spectrum antibiotics, mainly metronidazole (MDZ), tinidazole (TDZ), or clindamycin (CLI); antisetics (such as Octenisept(r), based on the detergent-like octenidin); probiotics (preparations of lactobacilli); and prebiotics (lactate gels). Although all of these treatments may have some beneficial effects, none have proven to have satisfactory efficacy in preventing recurrence. Antibiotics are the most effective in quickly reducing the symptoms, but they are associated with a recurrence rate of up to 60% within six months of treatment [26]. One reason may be the presence of an antibiotic-tolerant biofilm in BV that shelters a reservoir of persister cells [26; 27]. Antibiotic treatment not only often fails to eradicate the biofilm, but can also lead to further dysbiosis of the vaginal microbiome and can promote candidiasis [28].