Inhibition of bacteriophage K proliferation on Staphylococcus aureus in raw bovine milk

Aims: To assess the ability of staphylococcal bacteriophage K to inhibit Staphylococcus aureus in raw milk. Methods and Results: The ability of bacteriophage (phage) to replicate in milk is important in situations where phage might be used as a therapeutic for bovine mastitis. Phage K was able to replicate normally, leading to elimination of the host culture in milk, which had been previously heat-treated. When raw milk was used under identical conditions, the phages were unable to replicate. Phage adsorption assays were performed and these demonstrated that adsorption of phage was significantly reduced in the raw milk while it was restored in the heat-treated sample (86.50% compared with 99.96% adsorption respectively). When confocal microscopy with a Live/Dead Bac light staining system was employed, it was observed that in raw milk S. aureus formed clusters associated with fat globules, while in heat-treated milk, bacterial agglutination had not occurred. Conclusions: Raw milk inhibits staphylococcal phage K proliferation. Significance and Impact of the Study: This observation has implications for the exploitation of staphylococcal therapeutic phage in milk.