Encapsulation of bacteriophages to improve effective delivery to the intracellular bacterial pathogens

Bacterial antimicrobial resistance represents a significant challenge to global medicine. Bacteriophage therapy is receiving renewed attention as a promising alternative, or supplement, to conventional antimicrobials, however, bacteriophages do not penetrate eukaryotic cells well. This limits their use against intracellular bacterial pathogens, such as Mycobacterium tuberculosis and Rhodococcus equi (R. equi). Both these pathogens reside and grow within alveolar macrophages in lungs, infection requires long treatment and antimicrobial resistance is of concern.

One approach to overcome this limitation of bacteriophages, is delivery within liposomes, a well-established method for targeting drugs to sites of infection, including within eukaryotic cells. The aim of this project was to formulate and test liposome-encapsulated phage preparations for activity against intracellular Actinomycete pathogens,

Eight novel R. equi bacteriophages, including 4 which infect R. equi at 37°C, were isolated from soil samples collected at equine studs with a previous history of foal R. equi infections. Genomic and biological analysis of these bacteriophages revealed that these Siphoviruses share low genomic similarity. Based on size, host range, and kinetic features, R. equi phage AAM1 was selected for liposome encapsulation experiments. Different liposome lipid formulations and phage encapsulation efficiency were assessed.

Liposome encapsulated bacteriophage AAM1 had higher efficiency than free bacteriophages in treating R. equi infecting J774A.1 macrophages. Prophylactic treatment of macrophages with either bacteriophage preparation was unable to prevent the establishment of R. equi infection. Although free mycobacteriophage TM4 had no effect on M. bovis BCG when applied after uptake into THP-1 macrophages, application of liposome encapsulated TM4 resulted in a significantly higher numbers of intracellular BCG.

In conclusion, R. equi bacteriophages with therapeutic potential have been isolated. The preliminary evidence of efficacy of preparations of liposome encapsulated R. equi bacteriophage AAM1 in treating intracellular R. equi, supports the need for further studies and optimisation of liposome formulations.