# Synergistic Efficiency of a Novel Temperate Phage YF1204 and Amikacin Against Carbapenem-Resistant Pseudomonas aeruginosa and Its Biofilms

## TL;DR

A new temperate phage combined with amikacin shows strong antibacterial and anti-biofilm effects against drug-resistant Pseudomonas aeruginosa.

## Contribution

A novel temperate phage YF1204 is shown to synergize with amikacin to combat carbapenem-resistant Pseudomonas aeruginosa and its biofilms.

## Key findings

- Phage YF1204 belongs to the Siphoviridae family and has lytic activity against 41.4% of clinical isolates.
- Combining YF1204 with amikacin reduced the antibiotic's MIC by 2- to 8-fold and inhibited biofilm formation by 48.75%.
- The phage-amikacin combination showed no significant toxicity to THP-1 cells and achieved an 80% suppression index against CRPA.

## Abstract

Infections caused by carbapenem-resistant Pseudomonas aeruginosa (CRPA), especially chronic infections associated with biofilm formation, have become a major clinical challenge. Phage therapy has received much attention as an alternative strategy, but temperate phages have limited direct application due to their lysogenicity. The aim of this study was to explore the synergistic therapeutic effect of a novel temperate phage combined with antibiotics. A temperate Pseudomonas phage YF1204 was isolated from the patient’s bronchoalveolar lavage fluid and systematically characterized by whole-genome sequencing, transmission electron microscopy, and host range analysis. The synergistic antibacterial and anti-biofilm effects of phage with amikacin (AK) were evaluated by using the checkerboard test, a time-killing curve based on optical density (OD600) and crystal violet staining, and the cytocompatibility was analyzed by using the CCK-8 method. The results showed that phage YF1204 belonged to the Siphoviridae family and had typical temperate phage genome characteristics (containing integrase gene). It also showed lytic activity against 41.4% (87/210) of the clinical isolates, especially against carbapenem-resistant strains. When YF1204 was combined with AK, it reduced the minimum inhibitory concentration (MIC) of AK by 2- to 8-fold across all tested strains, respectively. Moreover, the inhibitory effect against CRPA was significantly enhanced (achieving suppression indexes about 80% ) and biofilm formation was inhibited with an inhibition ratio of 48.75%. Cell experiments showed that YF1204 had no significant toxicity to THP-1 cells. The combination of YF1204 and AK exhibited significant synergistic bactericidal and anti-biofilm activities, providing a novel therapeutic strategy with translational potential for CRPA-induced refractory infections.