# Therapeutic Optimization of Pseudomonas aeruginosa Phages: From Isolation to Directed Evolution

## TL;DR

Researchers isolated and improved three new phages that can target antibiotic-resistant Pseudomonas aeruginosa, showing promise for treating lung infections.

## Contribution

The study introduces three novel lytic phages and demonstrates how directed evolution can enhance their therapeutic potential.

## Key findings

- Phage Moonstruck showed superior lytic activity against P. aeruginosa when combined with ciprofloxacin.
- Directed evolution improved the killing efficacy of phage Nello but had less consistent effects on Moonstruck.
- Evolved phages had mutations in tail-associated genes, suggesting adaptation to better interact with their host.

## Abstract

Pseudomonas aeruginosa is a major opportunistic pathogen with high levels of antibiotic resistance. Phage therapy represents a promising alternative for the treatment of difficult infections both alone and in combination with antibiotics. Here, we isolated and characterized three novel lytic myoviruses, Cisa, Nello, and Moonstruck. Genomic analysis revealed that Cisa and Nello belong to the Pbunavirus genus, while Moonstruck is a novel Pakpunavirus species. All lacked lysogeny, virulence, or resistance-associated genes, supporting their therapeutic suitability. Phage Nello and Moonstruck were active against P. aeruginosa Pa3GrPv, isolated from a patient with lung infection candidate for phage therapy. Moonstruck exhibited superior lytic activity with ciprofloxacin sub-MIC value (0.125 µg/mL), achieving bacterial suppression for 48 h. However, to improve the lytic efficacy of the phages on the clinical isolate, phage adaptation via serial passage was investigated. The killing efficacy of Nello was enhanced, whereas Moonstruck showed a less consistent improvement, suggesting phage-specific differences in evolutionary dynamics. Sequencing of the evolved phages revealed point mutations in tail-associated genes, potentially linked to a better phage–host interaction. These results support the use of phage–antibiotic combinations and directed evolution as strategies to enhance phage efficacy against drug-resistant infections. Overall, these findings support the therapeutic potential of the newly isolated phages in treating P. aeruginosa lung infections.