With the increase of infections due to multidrug resistant bacterial pathogens and the\nshortage of antimicrobial molecules with novel targets, interest in bacteriophages as\na therapeutic option has regained much attraction. Before the launch of future clinical\ntrials, in vitro studies are required to better evaluate the efficacies and potential pitfalls\nof such therapies. Here we studied in an ex vivo human airway epithelial cell line model\nthe efficacy of phage and ciprofloxacin alone and in combination to treat infection by\nPseudomonas aeruginosa. The Calu-3 cell line and the isogenic CFTR knock down\ncell line (cftr-) infected apically with P. aeruginosa strain PAO1 showed a progressive\nreduction in transepithelial resistance during 24 h. Administration at 6 h p.i. of single\nphage, phage cocktails or ciprofloxacin alone prevented epithelial layer destruction\nat 24 h p.i. Bacterial regrowth, due to phage resistant mutants harboring mutations\nin LPS synthesis genes, occurred thereafter both in vitro and ex vivo. However, co-\nadministration of two phages combined with ciprofloxacin efficiently prevented PAO1\nregrowth and maintained epithelial cell integrity at 72 p.i. The phage/ciprofloxacin\ntreatment did not induce an inflammatory response in the tested cell lines as determined\nby nanoString gene expression analysis. We conclude that combination of phage\nand ciprofloxacin efficiently protects wild type and cftr- epithelial cells from infection\nby P. aeruginosa and emergence of phage resistant mutants without inducing an\ninflammatory response. Hence, phage-antibiotic combination should be a safe and\npromising anti-Pseudomonas therapy for future clinical trials potentially including cystic\nfibrosis patients.
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