Abstract: A double-layer plate method was used to isolate a virulent phage named T139 from sewage using Salmonella typhimurium (ATCC 13311) as the host strain, and the biological characteristics and antibacterial activity of phage T139 in milk and beef samples were studied. The results showed that phage T139 formed clear plaques; it could lyse its host bacterium and other Salmonella strains with a broad host spectrum. Transmission electron microscopic (TEM) observation showed that phage T139 belonged to the Podoviridae family with a head diameter of (43 ± 1) nm and a tail length of (11 ± 0.6) nm. The optimal multiplicity?of?infection (MOI) of this phage was 0.001, and the optimal adsorption rate was 66%. The one-step growth curve showed that the latent period was 5 min, the burst period was 60 min, and the average lysis amount was 54.54 PFU/cell. The phage was stable within 30–50 ℃ and pH 4–12. It had a good lytic effect on S. typhimurium cultured in vitro. The antibacterial effect of phage T139 on S. typhimurium in milk was not significant at 4 ℃, and the number of host cells decreased by 4.32 and 4.27 (lg (CFU/mL)) at MOI = 10 and 100 at 25 ℃, respectively. Similarly, it had no significant effect on S. typhimurium in beef at 4 ℃, MOI = 10, whereas at MOI = 100, the number of host cells decreased by 0.66 (lg (CFU/mL)). At 25 ℃, MOI = 10 and 100, the number of host cells decreased by 0.77 and 1.16 (lg (CFU/mL)), respectively. It was shown that phage T139 could effectively inactivate S. typhimurium in milk and beef.

Key words: Salmonella typhimurium, lytic phage, biological characteristics, antibacterial effect