Efficacy and Safety of a Bovine-Associated Staphylococcus aureus Phage Cocktail in a Murine Model of Mastitis

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.

Potentiële therapeutische toepassing van bacteriofagen en faag-afgeleide endolysinen als alternatieve behandeling van boviene mastitis

“…It may therefore be useful to develop cocktails consisting of different bacteriophages or to supplement the phage therapy with endolysins. The expansion of the working spectrum has already been tested and confirmed by two recent studies (Porter et al, 2016;Breyne et al, 2017). The main disadvantage of the classical endolysins remains their Gram-positive spectrum.…”

“…A selected phage cocktail for the treatment of S. aureus-associated (Newbould 305) bovine mastitis has recently been tested in vitro and in a mouse model (Breyne et al, 2017). First, different cultures were verified in the presence or absence of IgG and the phage cocktail.…”

“…A third group was injected with the phage cocktail. Breyne et al (2017) reported that S. aureus could not be isolated from the mice which were injected with cefalonium. In contrast, S. aureus was still present in the phagetreated group although the number of colony forming units (CFU) was significantly lower when compared to the negative control group.…”

The use of bacteriophages to control and detect pathogens in the dairy industry

“…saw a reduction in the bacterial load in mammary tissue in comparison with the phage‐free control. An improvement in mammary gland pathology was also observed post‐treatment (Breyne et al ). A similar study by Iwano et al .…”

Framing the Future with Bacteriophages in Agriculture

“…S. aureus , one of the etiological agents for mastitis, which has a propensity to recur chronically, causes a potentially fatal inflammatory response in gland tissues. In an experimental model, lactating mice intramammarily infected with a clinical bovine S. aureus strain showed significant improvement in mammary gland pathology and a 4-log reduction in bacterial load after phage treatment [ 32 ]. However, compared to the antibiotic cefalonium, the phage treatment was far less effective.…”