Background and Aim: This study was carried out to isolate lytic bacteriophages against Pseudomonas aeruginosa and analyze their biological characteristics and antibacterial effects on other clinical isolates of bacteria. Materials and Methods: Isolating two lytic bacteriophages against two strains of P. aeruginosa was carried out using the double-layer agar method. After investigating the antibacterial potential of the phages, the morphology of both phages was studied. The absorption rate and one-step growth curve of each phage were also determined. The survival rate of isolated phages was evaluated against different physical conditions, chemicals, and organic solvents. Then, the antibacterial potential of phages against clinical multidrug-resistant isolates of P. aeruginosa, Staphylococcus aureus, Escherichia coli, and Klebsiella pneuminiae, as well as standard strains of P. aeruginosa ATCC 27853, P. aeruginosa ATCC 9027, K. pneumonia ATCC 1290, S. aureus ATCC 25923, and Salmonella enterica ATCC 19430 and E. coli ATCC 8739, was determined. Results: One of the phages showed antibacterial effects on 50% of P. aeruginosa. Both phages had a high absorption rate, short latent period, and high burst size. Isolated bacteriophages belonged to the Cystoviridae family, and the highest stability of phages (PPaMa3/19 and PPaMa4/19) was observed at pH= 7 and a temperature of 4°C. The organic solvents and ionic detergents used in this study decreased the titers of both phages. Also, the highest anti-phage activity belonged to ethanol and acetone. PPaMa4/19 phage, unlike PPaMa3/19, was also lethal against E. coli (40%) and S. aureus (20%) bacteria. Conclusion: Phage PPaMa4/19 had high antibacterial potential against P. aeruginosa, S. aureus, and E. coli bacteria. What's more, it can be used for therapeutic purposes after more analysis. It is essential to consider the biological characteristics of phage stability and its resistance to infection treatment.
