Characterization, genome analysis, and therapeutic evaluation of a novel Salmonella phage vB_SalS_JNS02: a candidate bacteriophage for phage therapy

Phage therapy is gaining momentum as an alternative to antibiotics in the treatment of salmonellosis caused by Salmonella. In this study, a novel Salmonella phage, vB_SalS_JNS02, was isolated successfully from poultry farms in Shandong, China. The biological characteristics of vB_SalS_JNS02 were analysed, which revealed a short latent period of approximately 10 min and a burst size of 110 PFU/cell. Moreover, vB_SalS_JNS02 exhibited remarkable stability across a wide pH range (pH 3-12) and temperatures ranging from 30 to 80 °C. Genome sequencing analysis provided valuable insights into the genetic composition of vB_SalS_JNS02, which consists of a double-stranded DNA genome that spans 42,450 base pairs and has a G + C content of 49.4%. Of significant importance, the genomic sequence of vB_SalS_JNS02 did not contain any genes related to lysogenicity, virulence, or antibiotic resistance. The phage's efficacy was evaluated in a larval challenge study. Treatment with the phage resulted in increased survival of Galleria mellonella larvae (100%, 70%, and 85%) (MOI 0.1) in the prophylactic treatment, co-infection treatment, and remedial treatment experiments, respectively. Another in vivo experiment investigated the potential application of the phage in broiler chickens and revealed that a single oral dose of vB_SalS_JNS02 (108 PFU/mL, 100 µL/chick) administered 3 h after S. enteritidis oral administration provided effective protection. The introduction of bacteriophage not only enhances the production of secretory immunoglobulin A (sIgA), but also induces alterations in the composition of the gut microbial community. Phage therapy increases the relative abundance of beneficial bacteria, which helps to maintain intestinal barrier homeostasis. However, it is unable to fully restore the disrupted intestinal microbiome caused by S. enteritidis infection. Importantly, no significant adverse effects were observed in the animal subjects following oral administration of the phage, and our findings highlight vB_SalS_JNS02 is a hopeful candidate as a promising tool to target Salmonella infections in poultry.