As warned by Sir Alexander Fleming in his Nobel Prize address: “the use of antimicrobials can, and will, lead to resistance”. Antimicrobial resistance (AMR) has recently increased due to the overuse and misuse of antibiotics, and their use in animals (food-producing and companion) has also resulted in the selection and transmission of resistant bacteria. The epidemiology of resistance is complex, and factors other than the overall quantity of antibiotics consumed may influence it. Nowadays, AMR has a serious impact on society, both economically and in terms of healthcare. This narrative review aimed to provide a scenario of the state of the AMR phenomenon in veterinary medicine related to the use of antibiotics in different animal species; the impact that it can have on animals, as well as humans and the environment, was considered. Providing some particular instances, the authors tried to explain the vastness of the phenomenon of AMR in veterinary medicine due to many and diverse aspects that cannot always be controlled. The veterinarian is the main reference point here and has a high responsibility towards the human–animal–environment triad. Sharing such a burden with human medicine and cooperating together for the same purpose (fighting and containing AMR) represents an effective example of the application of the One Health approach.

Bovine mastitis is a major concern for the dairy cattle community worldwide. Mastitis, subclinical or clinical, can be caused by contagious or environmental pathogens. Costs related to mastitis include direct and indirect losses, leading to global annual losses of USD 35 billion. The primary treatment of mastitis is represented by antibiotics, even if that results in the presence of residues in milk. The overuse and misuse of antibiotics in livestock is contributing to the development of antimicrobial resistance (AMR), resulting in a limited resolution of mastitis treatments, as well as a serious threat for public health. Novel alternatives, like the use of plant essential oils (EOs), are needed to replace antibiotic therapy when facing multidrug-resistant bacteria. This review aims to provide an updated overview of the in vitro and in vivo studies available on EOs and their main components as an antibacterial treatment against a variety of mastitis causing pathogens. There are many in vitro studies, but only several in vivo. Given the promising results of treatments with EOs, further clinical trials are needed.

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.

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 pathogens associated with 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 related to bovine mastitis: S. agalactiae, S. dysgalactiae, S. uberis, S. 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 S. aureus and S. epidermidis. Results: Origanum vulgare and Cinnamomum verum resulted to be the EOs with the highest activity against the above-mentioned bacteria, inhibiting both bacterial growth and biofilm formation. Conclusions: This study emphasizes the relevance of investigating natural products and supports the hypothesis of appropriate 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.