Isolation and characterization of lytic bacteriophages against Salmonella enterica serovar Typhimurium from poultry farms and rivers in Addis Ababa, Ethiopia

Background Antimicrobial resistance (AMR) is a growing worldwide challenge, treatment options for bacterial infections are increasingly limited. Non-typhoidal Salmonella (NTS), particularly Salmonella enterica serovar Typhimurium, poses a serious threat to public health due to rising antimicrobial resistance. It can cause invasive bloodstream infections that have a high death rate. This study aimed to identify and isolate putatively lytic bacteriophages that target S . Typhimurium (ATCC 13311) from river water and poultry farm environments in Addis Ababa, Ethiopia and assessed their potential as candidate therapeutic phages. Method A total of 38 environmental samples were collected from poultry farms and rivers. From these samples, 22 bacteriophages were isolated using S . Typhimurium (ATCC13311) as the host strain. Spot assays were used to isolate phages, and the double-layer agar method (DLA) was used for purification. Characterization of phages performed by PCR-based identification and classification, latent period determination, plating efficiency, stability testing, and assessment of in vitro bactericidal activity. Results The majority (63.6%) were isolated from river water samples. Host range analysis showed that all isolates were active against the primary host, and four isolates showed cross-genus efficacy against specific pathotypes of Escherichia coli . The latent periods of the isolated phages ranged from 10 to 20 min, indicating a wide range of infection kinetics. Some of the most productive isolates attained Peak titers as high as 10¹³ plaque forming unit per mL(PFU/mL), indicating significant replication capacity. Additionally, the ideal multiplicity of infection differed significantly amongst isolates, ranging from 0.001 to 100. Regarding environmental stability, all phages were active in a pH range of 5 to 9 and withstood temperatures ranging from 4 °C to 37 °C. Molecular analysis classified most isolates into the T4-like and T7-like lineages. Conclusion The findings of this study suggest that the isolated phages may have potential as candidate biocontrol agents against S . Typhimurium. However, further characterization, including whole-genome sequencing, in vivo studies, and clinical trials, is necessary to confirm their taxonomic identity, therapeutic effectiveness, and safety. Clinical trial number Not applicable.