In vitro evaluation of a novel bacteriophage cocktail as a preventative for bovine coliform mastitis.

Mastitis control by means other than antibiotic treatment is one of the research topics of Milk SA. The UKZN in this regard is investigating the efficacy of bacteriophages and bacteriocins against Staphylococcus aureus as major mastitis-causing pathogen. Bacteriophages are viruses which attack the pathogen whereas bacteriocins are chemical substances produced by normal bacteria in the system which are toxic to invading bacteria such as Staph. aureus. The initial results at UKZN are promising; therefore it will be interesting to see results from elsewhere. Such a study was reported by Dr J. Porter and colleagues in the Journal of Dairy Science, Volume 99 of 2016, page 2053 to 2062. The title of their study is: In vitro evaluation of a novel bacteriophage cocktail as a preventative for bovine coliform mastitis.

 The objective of their study was to investigate the potential use of bacteriophages in preventing Escherichia coli mastitis in dairies. A cocktail consisting of four distinct bacteriophages was generated by screening in the laboratory against 36 E. coli isolates from dairy cows in Washington State with clinical mastitis. The bacteriophage significantly inhibited growth of 58% of the Washington State isolates and 54% of E. coli mastitis isolates from New York State, suggesting that the cocktail of phages had a relatively broad spectrum of action against relevant strains from two distinct areas. The ability to suppress bacterial growth of these isolates in a liquid growth medium was not affected by the ratio of bacteriophage particles to bacterial cells. A 3.3- to 5.6-log reduction of growth was achieved when E. coli was co-incubated with the phage cocktail in raw milk over a 12 hour period at room temperature. A developed assay using udder epithelial cells provided a model to test whether bacteriophage could prevent cell attachment and invasion by chronic coliform mastitis strains. Pre-treatment of cell cultures with the phage cocktail significantly reduced adhesion and intracellular survival of E. coli compared with controls. When combined with a bismuth-based teat sealant, the phage cocktail was able to inhibit bacterial growth when challenged with 1.6 × 10³ cfu/mL of a clinical mastitis E. coli strain.

The results show bactericidal activity by the phage cocktail both in raw milk and in the udder tissue culture. However, although promising, before a bacteriophage-based dry-cow treatment becomes a potential option for dairies, field studies must be able to demonstrate that a specific dose of bacteriophage can protect cows from experimentally induced E. coli mastitis without inducing an inflammatory reaction.