Abstract: Objective: Staphylococcus aureus was used as the host bacterium for isolating a lytic bacteriophage vB_SauM_RS. Its biological characteristics were determined, and its antibacterial effect in milk and its efficiency in removing biofilms were studied. Methods: Bacteriophage and S. aureus were inoculated together into skim milk or whole milk at a ratio of 1:100, which was then kept at 4 or 25 ℃. At different time points, bacterial concentration and phage titer were determined and the phage’s antibacterial effect was evaluated. Then, by crystal violet staining, plate counting method and double-layer agar plate method, bacterial concentration in the biofilm of S. aureus and phage titer were determined at different time points during phage treatment, the effect of the phage on the removal of biofilms formed on the surface of different materials was analyzed, and the changes in the number of bacterial cells in the biofilm before and after being removed were observed by fluorescence microscope. Results: Phage vB_SauM_RS formed clear plaques with halo; transmission electron microscopic (TEM) observation showed that the phage belonged to the Myoviridae family. The optimal multiplicity of infection (MOI) of this phage was 0.01. The one-step growth curve showed that the latent period was 20 min, and the average lysis amount was 39 PFU/cell. The phage was stable at 20–50 ℃ or pH 4.0–11.0. It inhibited the host bacterium, reducing the bacterial concentration in skim milk and whole milk by 1.079 (lg(CFU/mL)) and 1.021 (lg(CFU/mL)) after 24 h incubation at 4 ℃, and by 5.418 (lg(CFU/mL)) and 5.740 (lg(CFU/mL)) after 24 h incubation at 25 ℃, respectively. The results of plate counting and fluorescence microscopic observation showed that this phage had a clear effect on the clearance of bacterial cells in the biofilm, and of biofilms formed on the surface of all tested materials. Conclusion: Phage vB_SauM_RS not only has a good lytic effect on S. aureus in milk, but also can effectively remove the biofilm formed by S. aureus. It is promising as an antibacterial bioagent for preventing and controlling S. aureus.

Key words: lytic bacteriophage; Staphylococcus aureus; biological characteristics; milk; biofilm