Recurrent bacterial vaginosis
Bacterial vaginosis (BV) is the most common vaginal dysbiosis in reproductive-age women and is driven by the replacement of protective Lactobacillus species with a polymicrobial, Gardnerella vaginalis-anchored biofilm adherent to the vaginal epithelium. Standard antibiotics (metronidazole, clindamycin) clear symptoms but penetrate this biofilm poorly and indiscriminately suppress commensal lactobacilli, so recurrence within 3-12 months exceeds 50-60%. Phages and especially phage-derived endolysins are well suited here because they can be made exquisitely genus-specific for Gardnerella, leaving the protective lactobacilli intact, and because endolysins enzymatically degrade the peptidoglycan scaffold that holds the biofilm together. This targeted, biofilm-dissolving, resistance-resilient mode of action directly addresses the two failure points of antibiotics: biofilm recalcitrance and collateral damage to the healthy microbiome.
How phages act here
Mechanism
Two related strategies are in play. (1) Lytic Gardnerella phages (e.g., vB_Gva_AB1) infect and lyse specific clinical strains, but Gardnerella's deep strain/clade diversity makes whole-phage host range narrow, which motivates cocktail approaches. (2) The more advanced strategy uses recombinant/engineered phage endolysins (peptidoglycan hydrolases) applied directly as proteins. The lead molecule, PM-477/BNT331, is a genetically engineered, domain-optimized endolysin whose cell-wall-binding domain confers genus-level specificity: it kills all tested Gardnerella species (MIC90 ~1 ug/mL) yet does not lyse Lactobacillus crispatus, L. iners, or other commensals. Critically, endolysins attack peptidoglycan from the outside, so they physically dissolve established Gardnerella biofilms at low microgram concentrations (minimum biofilm eradication concentrations of 1-4 ug/mL), outperforming metronidazole and clindamycin in biofilm assays. Because they act on a conserved structural target rather than a metabolic pathway, resistance develops far more slowly than to antibiotics (only a marginal MIC rise after 25 passages, versus rapid high-level metronidazole resistance). This selectivity also preserves the option of phage-antibiotic or phage-probiotic synergy (debulking biofilm to let lactobacilli re-colonize).
Where it stands
Current evidence
Evidence has progressed from preclinical to first-in-human. PhagoMed Biopharma (acquired by BioNTech in 2021) developed the engineered Gardnerella endolysin PM-477, later clinical candidate BNT331. Robust preclinical data (Landlinger et al., 2022) showed Gardnerella-selective killing, superior biofilm eradication, and resistance avoidance. A 2025 ex vivo pharmacodynamics study (Tisakova et al., npj Biofilms and Microbiomes) treated vaginal samples from 49 women with BV and achieved >=94% reduction of viable Gardnerella at 20-50 ug/mL over 19 hours while sparing/allowing proliferation of L. crispatus, and these data defined the human dose. BioNTech then ran a registered Phase I first-in-human trial of BNT331 (NCT06469164 / BNT331-01): a randomized, double-blind, placebo-controlled study of single ascending doses in healthy women (Part A) and multiple ascending doses in women diagnosed with BV (Part B), using a vaginal insert formulation. The trial started July 2024 and is listed as completed (primary completion July 2025). Separately, academic groups (Arroyo-Moreno et al., 2022) have identified dozens of additional anti-Gardnerella endolysins, broadening the pipeline. No phage/endolysin product is yet approved for BV; the field is at the Phase I / proof-of-concept stage.
Evidence confidence: medium
The data
Key studies & trials
- Tisakova LP, Schwebs T, Berdaguer R, von Freyberg M, Foessleitner P, Kieninger AK, Poljak A, Corsini L, Farr A. Endolysin selectively kills Gardnerella ex vivo in vaginal samples from women with bacterial vaginosis. npj Biofilms and Microbiomes. 2025;11(1):161. ↗
- Landlinger C, Oberbauer V, Podpera Tisakova L, Schwebs T, Berdaguer R, Van Simaey L, Vaneechoutte M, Corsini L. Preclinical Data on the Gardnerella-Specific Endolysin PM-477 Indicate Its Potential to Improve the Treatment of Bacterial Vaginosis through Enhanced Biofilm Removal and Avoidance of Resistance. Antimicrobial Agents and Chemotherapy. 2022;66(5):e02319-21. ↗
- Arroyo-Moreno S, Cummings M, Corcoran DB, Coffey A, McCarthy RR. Identification and characterization of novel endolysins targeting Gardnerella vaginalis biofilms to treat bacterial vaginosis. npj Biofilms and Microbiomes. 2022;8(1):29. ↗
- BioNTech SE. A Phase I Randomized, Double-blind, Placebo-controlled, Safety, Tolerability, and Pharmacokinetic Trial of BNT331 Administered in Single Ascending Doses in Healthy Women and Multiple Ascending Doses in Women Diagnosed With Bacterial Vaginosis (BNT331-01). ClinicalTrials.gov identifier NCT06469164; started 2024, status Completed. ↗
Who is working on it
Programs & centers
The possibility
If the Phase I results hold, BV could become the first common condition routinely treated with a phage-derived enzyme rather than an antibiotic, with a vaginal insert that dissolves the Gardnerella biofilm in hours while leaving protective lactobacilli to repopulate the niche. Pairing a genus-specific endolysin with a Lactobacillus crispatus probiotic could turn today's revolving door of recurrence into a one-and-done reset of the vaginal microbiome. Because endolysins target a conserved structural wall rather than a mutable metabolic pathway, this approach may stay effective for decades where antibiotics are already failing.