Palo Santo (Bursera graveolens) essential oil nanoemulsion: toxicological, antinociceptive and antimicrobial potential against bovine mastitis–associated strains

Bovine mastitis is one of the major challenges in dairy production, causing significant economic losses and emphasizing the need for alternatives to the indiscriminate use of antibiotics. Palo Santo (Bursera graveolens) essential oil (BEO) presents recognized biological properties that can be enhanced through nanoengineered delivery systems. This study aimed to chemically characterize the BEO of B. graveolens, develop a nanoemulsion containing the essential oil (BEO-NE), and evaluate its toxicological, antinociceptive, and antimicrobial activities against bovine mastitis-associated pathogens. The chemical composition of the BEO was determined by gas chromatography-mass spectrometry (GC-MS), identifying D-limonene (38.70%) as the major constituent. The BEO-NE was formulated using avocado oil as the oil phase and sodium alginate as a stabilizing agent. Toxicological and antinociceptive effects were assessed through in vivo assays, including acute toxicity, acetic acid-induced writhing, and the formalin test. Antimicrobial activity was evaluated by minimum inhibitory and bactericidal concentration assays against Staphylococcus spp., Corynebacterium bovis, Streptococcus uberis, and Prototheca bovis. The BEO-NE showed enhanced antimicrobial activity against Staphylococcus aureus, including MRSA isolates, while exhibiting lower efficacy against C. bovis and S. uberis compared with the free BEO, indicating pathogen-dependent selectivity. The formulation demonstrated a favorable safety profile, with no evidence of hepatotoxicity or behavioral alterations. The BEO also exhibited significant antinociceptive activity, mainly in the neurogenic phase of the formalin test (p < 0.05). In conclusion, the BEO-NE represents a promising strategy for controlling S. aureus, the main etiological agent of bovine mastitis, combining selective antimicrobial and antinociceptive effects.