Stability and purity of a bacteriophage cocktail preparation for nebulizer delivery

Abstract

The aim of this study was to determine the stability and purity of a phage cocktail to be delivered by nebulization. A cocktail of three phages active against Pseudomonas aeruginosa isolates from cystic fibrosis patients was developed for a potential nebulized formulation. The individual phages were examined for their retention of activity over time, while the phage cocktail was analysed for bacterial contaminant and endotoxin level according to regulatory requirements for nebulized products. The phage cocktail was nebulized using a Porta-neb nebulizer connected to an Anderson cascade impactor. The three phages retained activity over a period of 180 days storage at room temperature and at 4°C. Nebulized phages were recovered in the lower stages of the cascade impactor indicative of potential delivery deep into the lungs. The phage cocktail met bacterial limits but the endotoxin levels measured with the Limulus amoebocyte lysate (LAL) test remained considerably in excess of acceptable levels even following purification. These findings suggest that nebulization of phage is a viable delivery option; although, there is a need for appropriate depyrogenation strategies to remove bacterial endotoxins from phage-based preparations to meet regulatory requirements. With increasing reports of bacterial resistance to antibiotics and the lack of new antibiotics being produced, bacteriophage therapy is becoming an attractive alternative. There has been no published report on the quality assurance of bacteriophage product to date. This is the first study on the quality assurance of a Pseudomonas aeruginosa phage cocktail following pharmacopoeial requirements. The presence of bacterial endotoxin was found to be the key stumbling block for meeting regulatory criteria.