Isolation and characterization of Salmonella enteritidis bacteriophage Salmp-p6 for potential application.

The emergence of multidrug-resistant (MDR) Salmonella enteritidis poses a significant threat to public health and food safety, necessitating novel antibacterial strategies. In this study, a lytic phage, Salmp-p6, was isolated from livestock wastewater and systematically characterized. The phage exhibited strong lytic activity against multidrug-resistant S. enteritidis and third-generation cephalosporin-resistant Escherichia coli. Salmp-p6 demonstrated robust physicochemical stability, retaining infectivity across a wide pH range (3-11) and at temperatures up to 70 °C. One-step growth assays revealed a short latent period (10 min) and a high burst size (62 PFU/cell). In addition, the phage-derived endolysin Lys67 was cloned, expressed, and demonstrated antibacterial activity against S. enteritidis under membrane-permeabilizing conditions, with stability across diverse pH and temperature ranges. In vitro, Salmp-p6 effectively inhibited biofilm formation and disrupted mature biofilms, and in food contamination models (milk and pork), it significantly reduced bacterial load. In vivo validation using a Galleria mellonella infection model confirmed its therapeutic efficacy by improving host survival. Whole-genome analysis revealed the absence of known virulence, integrase, and antibiotic resistance genes, supporting the biosafety of Salmp-p6. These findings demonstrate the strong applicability of Salmp-p6 for phage-based control of MDR Salmonella in both clinical and food safety applications.