Multimodal molecular mechanisms of octanoic acid (OA) against recurrent mastitis causing pathogens.

Recurrent bovine mastitis is a global concern that causes substantial economic losses and is exacerbated by pathogen internalization into mammary epithelial cells, and the emergence of antimicrobial resistance. These challenges necessitate the development of alternative antimicrobial strategies with multimodal activity. In this study, the naturally occurring molecule octanoic acid (OA) was evaluated for its antimicrobial efficacy and multitargeted mode of action against mastitis-associated pathogens. OA exhibited rapid bactericidal activity within 1 h and significantly reduced bacterial pathogenicity by attenuating toxin activity and inhibiting pathogen adhesion and internalization into epithelial cells. Transcriptomic analysis of Staphylococcus aureus revealed extensive OA-induced transcriptional alterations across multiple functional categories, including virulence regulation, stress response, metabolism, DNA replication and repair, membrane-associated functions, and transport systems, suggesting a broad cellular response to OA exposure. OA treatment also upregulated endogenous antimicrobial peptide (AMP) gene expression in MAC-T cells and did not induce detectable resistance even after 30 serial passages. Membrane perturbation was supported by molecular dynamics simulations and validated experimentally using DiBAC assays. In vivo toxicity assessment using Galleria mellonella demonstrated no observable toxicity up to 1000 mM OA. In addition, quantum chemical, physicochemical, and ADME/Tox analyses provided predictive insights into the chemical stability, drug-likeness, and safety profile of OA. Collectively, these findings suggest that OA exerts a multifaceted antimicrobial effect and represents a promising candidate for the development of next-generation antimicrobials targeting recurrent and resistant infections. KEY POINTS: • Octanoic acid (OA) rapidly kills mastitis pathogens via multimodal mechanisms. • OA prevents adhesion and internalization and mitigates toxicity in vitro and in silico. • OA alters mRNA expression profiles, revealing key antimicrobial pathways.