Isolation, Characterization, and Application in Poultry Product of a Specific Salmonella Bacteriophage S55.

Salmonellosis occurs frequently worldwide, causing serious threats to public health safety. The abuse of antibiotics is increasing the antibiotic resistance in bacteria, thereby making the prevention and control of Salmonella more difficult. A phage can help control the spread of bacteria. In this study, S55, a lytic phage, was isolated from faecal samples obtained from poultry farms using Salmonella Pullorum ( S . Pullorum) as the host bacterium. This phage belongs to Siphoviridae and has a polyhedral head and a retraction-free tail. S55 showed a strong ability to lyse Salmonella serovars, such as S . Pullorum (58/60, 96.67%) and S . Enteritidis (97/104, 93.27%). One-step growth kinetics showed that the latent period was 10 min, burst period was 80 min and burst size was 40 pfu/cell. The optimal multiplicity of infection was 0.01, and the phage was able to survive at a pH of 4-11 and temperature of 40°C-60°C for 60 min. Complete genome sequence analysis revealed that the S55 genome length is 42,781 bp (GC content, 50.28%) and it contains 58 open reading frames (ORF), including 25 ORFs with known or assumed functions, without tRNA genes. Moreover, S55 does not carry genes that encode virulence or resistance factors. At different temperatures (4°C or 25°C), S55 was found to lower the populations of S . Pullorum and S . Enteritidis on chicken skin surface. Its bacteriostatic effect at 4°C was higher than that at 25°C. In conclusion, S55 can be considered a promising biological agent for the prevention and control of Salmonella .