Canine endometritis is commonly associated with bacterial infections caused by Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Streptococcus canis (S. canis), leading to reproductive disorders in dogs. With increasing concern regarding antimicrobial resistance, alternative therapeutic strategies are needed. This study evaluated the in vitro antibacterial activity and underlying mechanisms of protocatechuic acid (PCA) against clinical isolates of these pathogens obtained from dogs diagnosed with endometritis. The antibacterial efficacy of PCA was assessed by determining minimum inhibitory concentrations (MICs), minimum bactericidal concentrations (MBCs), and bacterial growth curves. PCA inhibited the growth of all three pathogens, with MIC values of 4 mg/mL for E. coli and S. aureus and 2 mg/mL for S. canis. The MBCs for E. coli and S. aureus were equal to their MICs, while the MBC for S. canis was twice the MIC, indicating bactericidal activity. Mechanistic analyses demonstrated that PCA disrupted bacterial membrane integrity, induced membrane depolarization, reduced intracellular ATP levels, and increased reactive oxygen species (ROS) accumulation. These effects were supported by SYTO9/PI fluorescence staining and scanning electron microscopy. In conclusion, PCA exhibits notable in vitro antibacterial activity against key pathogens associated with canine endometritis and represents a promising natural antimicrobial candidate.

Bovine mastitis is a common inflammatory disease that can progress to mammary fibrosis, thereby impairing udder health, milk yield, and milk quality. This study investigated the protective effects of palmatine on lipopolysaccharide (LPS)-induced epithelial–mesenchymal transition (EMT) in bovine mammary epithelial cells and mammary fibrosis in mice, as well as the underlying mechanisms. In vitro, palmatine markedly reversed LPS-induced EMT by increasing E-cadherin expression and decreasing N-cadherin and α-SMA expression. In vivo, palmatine alleviated inflammatory cell infiltration and collagen deposition in mammary tissue and reduced the expression of TGF-β1, p-Smad2, p-Smad3, p-p65, TNF-α, IL-1β, and IL-6. These findings suggest that palmatine alleviates LPS-induced mammary fibrosis, possibly through inhibition of the NF-κB/TGF-β1/Smad signaling pathway, and may represent a potential therapeutic strategy for the prevention and treatment of mammary fibrosis.