Ciprofloxacin in combination with bacteriophage cocktails against multi-drug resistant Pseudomonas aeruginosa in ex vivo simulated endocardial vegetation models

-associated infective endocarditis represents difficult-to-treat, deep-seated infections. Phage-antibiotic combinations have shown to eradicate multi-drug resistant (MDR) , limit the development of phage resistance, and restore antibiotic sensitivity. The objective of this study was to evaluate the activity of phage-ciprofloxacin (CIP) combinations in 4-day simulated endocardial vegetation (SEV) models against drug-resistant isolates. Two isolates, extensively drug-resistant AR351 and MDR I0003-1, were selected for their drug resistance and sensitivity to phage. Three phages [LL-5504721-AH (LL), E2005-C (EC), and 109] and CIP were evaluated alone and in combination for their activity and influence on drug and phage resistance using 24-h time-kill analysis. The three-phage cocktail (q24h) in combination with CIP (400 mg q12h) was then tested in dynamic 4-day SEV models, with reduction of log CFU/mL compared using ANOVA with Bonferroni analysis. Compared to other combinations, CIP-LL-EC-109 demonstrated synergistic and bactericidal activity from starting CFU/g against AR351 and I0003-1 (-Δ5.65 and 6.60 log CFU/g, respectively; < 0.001). Additionally, CIP-LL-EC-109 mitigated phage resistance, while all other therapies had a high degree of resistance to >1 phages, and all phage-containing regimens prevented CIP mean inhibitory concentration increases compared to CIP alone for both AR351 and I0003-1 at 96 h.