Repurposing metformin as a dual-function agent to combat E. coli-induced mastitis: Mechanistic insights into biofilm dispersion and AMPK/SIRT1-mediated NF-κB inhibition.

Escherichia coli-induced bovine mastitis represents a major challenge in dairy production due to the prevalence of multidrug-resistant strains. This study repurposes metformin as a dual-function agent that simultaneously targets bacterial virulence and host inflammation. Epidemiological surveillance identified phylogroup B1 as the most prevalent (52.5%) and resistant E. coli lineage. Against a representative B1 strain, metformin potently inhibited and dispersed bacterial biofilms, and synergized with conventional β-lactam antibiotics. Bacterial transcriptomics revealed metformin downregulated genes critical for membrane integrity and metabolism. In parallel, metformin attenuated the inflammatory response in bovine mammary epithelial cells and in murine and ovine mastitis models. In vivo, it significantly reduced bacterial colonization in mammary tissue and suppressed key pro-inflammatory cytokines. Mechanistically, metformin activated the AMPK/SIRT1 axis, leading to deacetylation of NF-κB p65. In the ruminant model, this culminated in epigenetic regulation, with increased chromatin compaction at promoters of inflammatory genes, and a significant inverse correlation (r = -0.77) between NF-κB binding and chromatin accessibility. Collectively, metformin combats resistant E. coli mastitis through a dual mechanism: disrupting biofilm-dependent bacterial persistence and reprogramming host immunometabolism via AMPK/SIRT1-mediated epigenetic regulation. These findings provide a compelling non-antibiotic strategy for overcoming antimicrobial resistance.