Isolation of lytic phage and its inhibition of multidrug-resistant Salmonella and its biofilm.

Abstract

Salmonella represents a prevalent foodborne zoonotic pathogen. The growing prevalence of drug-resistant strains in recent years underscores an urgent need for novel antimicrobial agents. In this study, a novel broad-spectrum Salmonella phage SPTA3 was successfully isolated and characterized. Biological and physicochemical analyses revealed that phage SPTA3 exhibits a broad host range, lysing 44 out of 95 tested Salmonella strains, including four serotypes: S. Enteritidis, S. Typhimurium, S. Kottbus, and S. Bovismorbificans. In terms of physicochemical properties, phage SPTA3 demonstrated considerable stability under varying temperature (40-70℃) and pH (3-12) conditions. The optimal multiplicity of phage SPTA3 infection was 0.00001. SPTA3 displayed a short latent period (30 min) and an extended lytic cycle (90 min), with a burst size of 143 PFU/cell. Genomic analysis further classified SPTA3 within the family Caudovirales and the genus Jerseyvirus. The genome encoded 30 functional protein sequences, including tail fiber proteins, tail spike proteins, as well as endolysin and holin involved in host lysis. Notably, the phage genome lacks tRNA genes, virulence factors, and antimicrobial resistance genes. Research demonstrated that phage SPTA3 effectively eradicated biofilms formed by S. Enteritidis 72 (71.9%) and S. Typhimurium JN21 (64.24%). Further evaluation using a duckling infection model revealed that oral administration of phage SPTA3 significantly reduced the Salmonella load in vivo, achieving a maximum reduction of 1.73 lg CFU/mL. These findings indicate that phage SPTA3 possesses notable preventive and control efficacy against biofilms, positioning it as a promising potential biocontrol agent for mitigating Salmonella transmission in poultry and food processing environments.