Abstract

Background: Pseudomonas aeruginosa is an opportunistic pathogen that is of particular importance in respiratory infections of Cystic Fibrosis patients. This in part is due to the ability of Ps. aeruginosa to develop as a biofilm within the mucus layers of CF patients reducing the effectiveness of antibiotic therapy and increasing predisposition to other respiratory pathogens. This decrease in effectiveness has lead to resurgence in interest in the use of lytic bacteriophages to combat such a bacterial infection. Methods: The activity of a cocktail of 3 phages was assessed against 14 strains of Ps. aeruginosa including clinically relevant strains using a novel automated screening assay over a period of 20 hours. The activity of the cocktail was also assessed against four strains of Ps. aeruginosa that had been cultured for 96 hours in a constant depth film fermentor. Following the use of the cocktail for 8 and 20 hours against the bacterial biofilm, phage infectivity was neutralized using pomegranate rind extract and the surviving numbers of bacteria quantified. The effects of alginate lyase and ambroxol hydrochloride in conjunction with the cocktail were also assessed. Results: When assessed with the automated assay, the phage cocktail showed the ability to reduce the number of bacteria at both 8 and 20 hours in all 14 strains. However, the level of reduction varied between strains. When the phage activity was assessed against a bacterial biofilm, there was a reduction in bacterial number between 0.5 and 1.0 log at 8 and 20hours in most cases, with only one strain (NCTC 10332) showing a significant re-growth following phage exposure. The addition of alginate lyase or ambroxol hydrochloride did not increase the efficacy of phages in a meaningful manner in all strains except against NCTC 10332. Conclusion: The assessment of the activity of Ps. aeruginosa cocktails can be rapidly and quantitatively assessed on the basis of multiple relevant criteria using an automated screening assay. Although the cocktail showed to be highly active against planktonic bacteria, reduction of bacterial biofilm was modest but encouraging.