Synergistic Potential of Bacteriophage and Blue Light Therapy Against Biofilm-Associated Klebsiella pneumoniae in Postoperative Gynaecological Infections

• Synergistic phage-blue light therapy achieved >82% biofilm reduction. • Sequential Phage first then Blue light treatment showed enhanced early bactericidal activity. • Blue light-induced ROS disrupted EPS, improving phage penetration and efficacy. • Dual treatment was non-cytotoxic and did not trigger inflammatory cytokines. • Combines physical and biological mechanisms for antibiotic-free wound therapy. Klebsiella pneumoniae, a prominent member of the ESKAPE pathogen group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species), represents a serious concern in postoperative gynaecological infections due to its multidrug resistance (MDR) and strong biofilm-forming ability. The limited efficacy of conventional antibiotics against such infections underscores the need for innovative combinatorial strategies, such as bacteriophage therapy and phototherapy. This study aimed to evaluate the synergistic antibacterial potential of bacteriophage therapy and blue light (450 nm) phototherapy against biofilm-associated MDR K. pneumoniae isolated from a post- cesarean wound infection. A clinically isolated MDR K. pneumoniae strain was characterised, and biofilms were treated with phage, blue light, or sequential phage-light combinations. Crystal violet assays and microscopy quantified biofilm biomass reduction, while synergy was analysed using the Bliss independence model. Phage stability under blue light and cytocompatibility with HiFi™ human PBMCs were also assessed, along with cytokine profiling. The combined phage-blue light treatment achieved an 82.3% reduction in biofilm biomass, significantly surpassing either monotherapy (p < 0.0001). Sequence-dependent synergy was observed, with Phage→Light treatments showing stronger early effects (6 h). Phage viability remained unaffected by blue light, and PBMC assays confirmed high cytocompatibility with no detectable cytokine induction. Mechanistically, blue light-induced ROS disrupted the biofilm matrix, facilitating enhanced phage penetration and infection. Bacteriophage-blue light combination therapy represents a safe, synergistic, and resistance-mitigating approach for managing MDR K. pneumoniae biofilm infections, offering promising translational potential in postoperative gynaecological wound care.