Combined Bacteriophage and Antibiotic Treatment PreventsPseudomonas aeruginosaInfection of Wild Type andcftr- Epithelial Cells

With the increase of infections due to multidrug resistant bacterial pathogens and the shortage of antimicrobial molecules with novel targets, interest in bacteriophages as a therapeutic option has regained much attraction. Before the launch of future clinical trials,in vitrostudies are required to better evaluate the efficacies and potential pitfalls of such therapies. Here we studied in anex vivohuman airway epithelial cell line model the efficacy of phage and ciprofloxacin alone and in combination to treat infection byPseudomonas aeruginosa. The Calu-3 cell line and the isogenic CFTR knock down cell line (cftr-) infected apically withP. aeruginosastrain PAO1 showed a progressive reduction in transepithelial resistance during 24 h. Administration at 6 h p.i. of single phage, phage cocktails or ciprofloxacin alone prevented epithelial layer destruction at 24 h p.i. Bacterial regrowth, due to phage resistant mutants harboring mutations in LPS synthesis genes, occurred thereafter bothin vitroandex vivo. However, co-administration of two phages combined with ciprofloxacin efficiently prevented PAO1 regrowth and maintained epithelial cell integrity at 72 p.i. The phage/ciprofloxacin treatment did not induce an inflammatory response in the tested cell lines as determined by nanoString(R)gene expression analysis. We conclude that combination of phage and ciprofloxacin efficiently protects wild type andcftr- epithelial cells from infection byP. aeruginosaand emergence of phage resistant mutants without inducing an inflammatory response. Hence, phage-antibiotic combination should be a safe and promising anti-Pseudomonas therapy for future clinical trials potentially including cystic fibrosis patients.