Developing a Non-aureus Staphylococcus Intramammary Probiotic as a Preventative Measure for Bovine Mastitis

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Bovine mastitis is the most common and economically important disease affecting the dairy industry. Intramammary infection (IMI) with Staphylococcus aureus is the leading cause of contagious mastitis. Interestingly, non-aureus staphylococci (NAS) are frequently found in cows with subclinical mastitis, but with a severity less than with S. aureus. Antibiotics are the main method for preventing and treating mastitis. Misuse and overuse of antibiotics have resulted in the emergence of antimicrobial-resistant bacteria, and thus, alternative treatments are required. Bacteriocins, antimicrobial peptides produced by bacteria, are a promising alternative. We hypothesized that by creating a NAS probiotic through genetically engineering a bacteriocin gene cluster into its genome, it will be able to inhibit S. aureus and prevent mastitis. To achieve this, we needed to find a persistent and non-inflammatory NAS strain that can colonize cow mammary glands by using an experimental mammary infusion model. After finding a persistent and non-inflammatory NAS, we will perform a bacteriocin gene cluster knock-in using allelic replacement. Finally, the probiotic will then be characterized through gene expression and killing assays. This thesis aimed to create an alternative treatment to prevent the growth of mastitis pathogens during the dry period. Ultimately, this will lower the usage of antibiotics and give us another preventative tool against mastitis. We identified S. warneri 2993 as the most persistent and non-inflammatory NAS but unfortunately, we were not able to perform our bacteriocin gene knock-in. Instead, we recommend future studies to re-attempt this gene knock-in but with a different bacteriocin gene cluster for an increased likelihood of success. The probiotic will then need testing in ¬in vivo¬ IMI experiments in mice and then in cows following the protocols we have designed.
Mastitis, Probiotic, Bovine, Non-aureus Staphylococcus, Genetic Manipulation, Transformation, Allelic Replacement
Vu, D. (2023). Developing a non-aureus staphylococcus intramammary probiotic as a preventative measure for bovine mastitis (Master's thesis, University of Calgary, Calgary, Canada). Retrieved from