Abstract: Based on the molecular tools to identify with rapidity,sensitivity,and specificity the major pathogens involved in intramammary infections in cows,a PCR-based assays of the highly divergent and species-specific regions of the DNA coding for 23S rRNA was employed. In this study,a novel virulent bacteriophage had been isolated from the waste water sample in a local dairy farm after three times enrichment in LB liquid medium co-cultured with S. aureus isolates. TEM observation of the isolated phage had an icosahedral capsid of 62.5 nm in diameter and a long (187.5 nm) with contractible tail,there was a connector linked the head and tail. As a tailed virus of bacteria,phage classified into the families of tailed viruses infected bacteria. The plaques of the phage were formed transparent uniformed,clear,round zones and their sizes were 2 mm in diameter. The titer of phage against S.aureus isolates was more than 10⁹ PFU/mL. Storage conditions of the phage were studied. The phage should store at -80 ℃ supplemented with 7% DMSO.

Key words: bovine mastitis; Staphylococcus aureus; virulent phage; isolation; storage