Antibacterial and Anti-Biofilm Activities of Essential Oils Against Etiological Agents of Bovine Mastitis

Background: The inflammation of the mammary gland, known as bovine mastitis, is a major challenge for the dairy cattle industry globally. The main organisms responsible for mastitis are bacteria, classified as either contagious, such as Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus agalactiae; or environmental, primarily Streptococcus spp. (e.g. Streptococcus uberis) and coliform species. Even though the emergence of antibiotic-resistant strains of pathogens poses a serious threat, antibiotics are still the primary treatment for mastitis. It is therefore necessary to explore alternative therapies, such as essential oils (EOs). This in vitro research intended to evaluate the efficacy of EOs against etiological agents of bovine mastitis, as an alternative or complementary treatment to conventional antibiotics. Methods: The bactericidal activity of eleven essential oils and two blends was tested on five strains causing bovine mastitis: Str. agalactiae, Str. dysgalactiae, Str. uberis, Sta. aureus, and Staphylococcus epidermidis. An assessment was carried out of both the reduction of biofilm formation and the inhibition of pre-formed biofilm against biofilm-formative strains of Sta. aureus and Sta. epidermitis. Results: Origanum vulgare and Cinnamomum zeylanicum resulted to be the EOs with the highest activity against the above-mentioned bacteria, inhibiting both bacterial growth and biofilm formation. Conclusions: This study emphasises the relevance of investigating natural products and supports the hypothesis of safe use of EOs to reduce bacterial infections and provide an effective alternative to antibiotics in complementary therapy. Moreover, to avoid treatment failure, the combined use of available antibiotics and natural compounds should also be considered.