Abstract
Overuse of antibiotics is a major problem in the treatment of bovine mastitis, and antibiotic treatment is frequently non-curative, thus alternative treatments are necessary. The primary aim of this study was to evaluate the efficacy of a purified phage cocktail for treatment of bovine Staphylococcus aureus mastitis in a well-defined mouse model. Candidate phages were selected based on their in vitro performance and subsequently processed into an optimally composed phage cocktail. The highest scoring phages were further tested for efficacy and resistance suppression in broth and raw milk, with and without supplemental IgG. As these in vitro results displayed significant decreases in CFU, the cocktail was purified for testing in vivo. Lactating mice were intramammarily inoculated with S. aureus N305 (ATCC 29740), a clinical bovine mastitis isolate commonly used for experimental infection of dairy cows. The phage cocktail was applied via the same route 4 h post-inoculation. Treated mammary glands were graded for gross pathological appearance and excised for bacterial and phage load quantification as well as histopathology. Observation of gross macroscopic and histopathological changes and CFU quantification demonstrated that the phage cocktail treatment significantly improved mastitis pathology and decreased bacterial counts. Phage PFU quantification indicated that the tested phage cocktail treatment was able to maintain high intramammary phage titers without spreading systemically. The in vivo results complement the in vitro data and support our concept of phage therapy as an innovative alternative or supplementation therapy to antibiotics for the treatment of bovine mastitis.
Highlights
Bovine mastitis is the most prevalent disease impacting United States dairy cattle (USDA, 2007)
Despite the antibiotic sensitivity that most S. aureus mastitis isolates display in vitro (Erskine et al, 2006; Lindeman et al, 2013), they are more difficult to eliminate in vivo with reported clinical mastitis cure rates as low as 4% (Barkema et al, 2006)
The current study investigated the potential of phage therapy for the treatment of bovine staphylococcal mastitis, by combining complementary in vitro and in vivo strategies
Summary
Bovine mastitis is the most prevalent disease impacting United States dairy cattle (USDA, 2007). A withholding period is imposed after completing a course of antibiotic therapy in dairy cattle to allow the animal to eliminate the antibiotic from its system prior to returning to production for human consumption. The length of this period is determined by route of administration and pharmacokinetic properties of the specific drug, and residue studies are performed prior to product approval to determine when milk and meat from the cows is acceptable for consumption. If phage therapy were to be granted a zero withholding period based on a positive human food safety profile, the presence of any residual phage in meat or milk would be of no concern, it would benefit producers by reducing losses due to discarded milk and if appropriate, send cattle to slaughter sooner
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