Antibacterial efficacy of lytic Pseudomonas bacteriophage in normal and neutropenic mice models

Recently, lytic bacteriophages (phages) have been focused on treating bacterial infectious diseases. We investigated the protective efficacy of a novel Pseudomonas aeruginosa phage, PA1Ø, in normal and neutropenic mice. A lethal dose of P. aeruginosa PAO1 was administered via the intraperitoneal route and a single dose of PA1Ø with different multiplicities of infection (MOI) was treated into infected mice. Immunocompetent mice infected with P. aeruginosa PAO1 were successfully protected by PA1Ø of 1 MOI, 10 MOI or 100 MOI with 80% to 100% survival rate. No viable bacteria were found in organ samples after 48 h of the phage treatment. Phage clearing patterns were different in the presence or absence of host bacteria but PA1Ø disappeared from all organs after 72 h except spleen in the presence of host bacteria. On the contrary, PA1Ø treatment could not protect neutropenic mice infected with P. aeruginosa PAO1 even though could extend their lives for a short time. In in vitro phage-neutrophil bactericidal test, a stronger bactericidal effect was observed in phage-neutrophil co-treatment than in phage single treatment without neutrophils, suggesting phage-neutrophil co-work is essential for the efficient killing of bacteria in the mouse model. In conclusion, PA1Ø can be possibly utilized in future phage therapy endeavors since it exhibited strong protective effects against virulent P. aeruginosa infection.