Abstract: Isolation of an appropriate lytic phage against Salmonella Typhimurium will help to provide a biological for controlling infection or pollution caused by this pathogen. A strain of Salmonella Typhimurium with multidrug resistance which had been isolated from bulk milk was used as host bacteria. Artificial induction method was employed. Three chickens were fed daily with the host bacterium suspension for a week. After 7 days, the phage isolation and culture was conducted from chicken feces by using double agar plate method. The titer, nucleic acid type, host spectrum, thermal and acid-base stability and therapeutic effect in Salmonella Typhimurium infected mice using the phage were analyzed. A lytic phage against Salmonella Typhimurium was isolated and purified, named KM104. This phage efficiently lysed the homologous host strain and another Salmonella Typhimurium strains in vitro, producing clear and circular plaques with a diameter of about 1 mm. The viral nucleic acid type was DNA and its genome size was 28 kb or so. The highest titer of the virus was 4.6×10⁸ PFU·mL^-1. The optimal multiplicity of infection (MOI) was 1:10, the incubation period was approximately 6 min, and it reached the highest titer at 70 min. The phage maintained high viability under the condition of 20-60℃ and a pH value range of 2.0-8.0. The phage effectively reduced the injury in duodenal tissue of experimental mice caused by Salmonella Typhimurium. The results here indicated that KM104 can efficiently lyse Salmonella Typhimurium in vivo and in vitro with rapid proliferation and strong adaptability to the environment. Its acid-fast character is expected to help resist the degradation by gastric acid, making the phage have a potential application value in preventing and controlling Salmonella Typhimurium infection or pollution.

Key words: Salmonella Typhimurium, lytic phage, biological properties, biological control