Exploiting phage-antibiotic synergies to disrupt Pseudomonas aeruginosa PAO1 biofilms in the context of orthopedic infections

ABSTRACT In recent years, bacteriophages (or phages) have reentered the spotlight as alternative or adjuvant therapeutic agents to antibiotics. Their efficacy in more recalcitrant forms of infections like biofilms, frequently encountered in the orthopedic setting, remains less characterized. The present study aimed at evaluating the activity of phage-antibiotic combinations against Pseudomonas aeruginosa biofilms. A large collection of phages was de novo isolated from a wide variety of environmental sources. Three phages with a large host range against a.o. clinical orthopedic isolates, PSP2 (Yuavirus), PSP3 (Pbunavirus), and PSP30 (Bruynoghevirus), were selected for phage-antibiotic synergy assays on mature P. aeruginosa PAO1 biofilms. Phages were combined with ciprofloxacin, meropenem, and ceftazidime, all used as standard of care in bone-related infections. Significant reductions in both cell counts and biomass were observed for all phage-antibiotic combinations. The highest reduction in viable cell counts was observed for PSP3 and PSP2 in combination with ceftazidime [4.58 and 4.30 log10 Colony Forming Units (CFU)/well], followed by all phage combinations with ciprofloxacin (up to 3.56 log10 CFU/well). The highest reduction in biomass was obtained by combining PSP3 with ciprofloxacin (29.8%). Metabolic assays confirmed these findings with reductions in biofilm respiratory rate of up to 65%. Scanning electron microscopy imaging of PAO1 biofilms grown on titanium coupons and treated by ciprofloxacin and PSP30 confirmed the efficacy of the combined treatment with PSP30 and ciprofloxacin. This study highlights the synergetic effects of phage-antibiotic combinations on P. aeruginosa biofilms, thereby offering a promising approach to combat biofilm-associated infections. IMPORTANCE Biofilm-related infections are among the most difficult-to-treat infections in all fields of medicine due to their antibiotic tolerance and persistent character. In the field of orthopedics, these biofilms often lead to therapeutic failure of medical implantable devices and urgently need novel treatment strategies. This forthcoming article aims to explore the dynamic interplay between newly isolated bacteriophages and routinely used antibiotics and clearly indicates synergetic patterns when used as a dual treatment modality. Biofilms were drastically more reduced when both active agents were combined, thereby providing additional evidence that phage-antibiotic combinations lead to synergism and could potentially improve clinical outcome for affected patients.