Mastitis (inflammation of the mammary gland) in dairy cows is a problem that leads to significant losses for farms and is also a cause of overuse of antibiotics and, consequently, the spread of antibiotic resistance. Bacteriophages are currently being considered as a promising alternative to antibiotics for the prevention and treatment of mastitis in dairy cows.

Chinese researchers tested* a phage cocktail in a laboratory model of mastitis. They isolated the Staphylococcus aureus strain Sau-XJ-21 from the milk of cows with mastitis and isolated two bacteriophages (designated vBSM-A1 and vBSP-A2) with potent lytic activity against Sau-XJ-21 from the farm's wastewater. Phages vBSM-A1 and vBSP-A2 belonged to the Myoviridae and Podoviridae families, respectively, and had a broad (especially vBSM-A1) spectrum of target bacteria.

To determine the efficacy of phages against mastitis, lactating female mice were used 10-14 days postpartum. The animals were divided into six groups, one of which served as a control, while the others were inoculated with S. aureus to induce mastitis. Four hours after inoculation, the mice were administered either saline (negative control), the cephalosporin antibiotic ceftiofur (positive control), or the vBSM-A1 and vBSP-A2 phages—either a single strain or a cocktail.

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After 20 hours, the mammary glands of the experimental mice were subjected to microbiological and cytological examination. In mice with mastitis, a significant improvement in the clinical picture and a reduction in bacterial load were observed in the groups receiving bacteriophages, with the effect being most pronounced with the phage cocktail. High phage titers were observed in the mammary glands without systemic dissemination. The antimicrobial effect of the phage cocktail was comparable to that of the antibiotic ceftiur.

The authors conclude that bacteriophages can be considered as a safe and effective alternative to antibiotics in the treatment of mastitis in cows.

* Geng H., Zou W., Zhang M. et al. Evaluation of phage therapy in the treatment of Staphylococcus aureus -induced mastitis in mice. Folia Microbiol 65, 339–351 (2020). https://doi.org/10.1007/s12223-019-00729-9