A novel Staphylococcus phage, vB_Sau-RP15, and its application in contaminated milk

The vB_Sau-RP15 phage, selected for its potential use as a phage treatment in milk, was isolated from raw milk using Staphylococcusaureus NP01 as the host. The host range test revealed that the phage was able to lyse 12 strains of Staph. aureus from raw milk. This phage was stable at 4-37°C and pH 6-9 for at least 1 h. The adsorption rate was ~78% within the first 3 min. A low frequency of phage-insensitive mutant induction (4.6 × 10-6) was observed. Genomic analyses revealed that the vB_Sau-RP15 represented a novel species in the genus Silviavirus. Even though no virulence or antibiotic resistance genes were detected, the phage genome carried lysogenic-associated genes. Phage treatments (108 PFU per ml) in pasteurized milk contaminated with low (104 CFU per ml) and high (107 CFU per ml) concentrations of Staph. aureus confirmed the proficiency of the phage in the diminishing of the number of bacterial cells at 4°C and ambient temperature. A Staphylococcus phage, vB_Sau-RP15, could be a promising agent for controlling Staph. aureus contamination in milk.