Pre-clinical studies on therapy of Staphylococcus aureus Mastitis by bacteriophage in mice model

With the rising prevalence of antibiotic-resistant bacteria, alternatives to treatment with antibiotics are receiving increased attention. One option is therapeutic use of bacteriophages. Since Staphylococcus aureus is accepted as the most problematic organism associated with bovine mastitis throughout the world, a study on assessment of therapeutic efficacy of a specific lytic phage against a mastitogenic S. aureus isolate was undertaken using murine mammary gland as a model for the study. Fourteen S. aureus cultures were isolated from 52 bovine and buffalo mastitis cases. Lytic bacteriophage against each S. aureus isolate was purified and characterized with respect to its host range. On the basis of the clinical history of the animal, 1 isolate was selected for the experiment. Therapeutic phage stock against the experimental organism was prepared and plaque forming units/ml of the stock was determined. Trials were conducted in R-4 and L-4 inguinal mammary glands of 7 day post litter mice groups challenged with approximately 10⁷ colony forming units (CFUs) of the S. aureus strain. Single injection of approximately 2x10⁷ pfu of the phage particles was given through intramammary (i.mam) or intravenous (i.v) route 24 hrs after challenge infection. Mammary glands were externally examined and collected for bacterial counts, detection of phage and histopathology after 24, 48 and 72hrs of phage inoculation. Suitable groups of infected, saline injected and uninfected control animals were also incorporated. Complete recovery evidenced by (i) elimination of challenge organism with detection of phage in the mammary tissue (ii) complete reduction in swelling and return to normalcy in histopathological sections was observed at 48h in the i.v treated group. In the i.mam group, similar recovery was observed at 72hrs of therapeutic inoculation. Though, recovery through i.v inoculation was faster, the route was not found absolutely safe. Murine mammary gland model appeared satisfactory for conducting safety and potency trials of therapeutic phage stocks.