Lactic Acid Bacteria Metabolites Modulate Immune Response Against Staphylococcus haemolyticus-Infected RAW264.7 Murine Macrophage: A Novel Approach for Bovine Mastitis

Bovine mastitis, an inflammation of the mammary gland, is recognized as the most prevalent disease in dairy cattle, leading to significant economic losses due to the reduction in quality and yield of milk. While antibiotic treatment remains to be the primary control method but their use of antibiotics contributes to the emergence of antibiotic-resistant bacteria and possesses potential health risks to consumers. Enhancement of host immune responses represents a promising alternative strategy for combating pathogenic bacteria. This study aimed to evaluate the immunomodulatory potential of metabolites derived from lactic acid bacteria (LAB) in murine macrophage RAW264.7 cells infected with Staphylococcus haemolyticus, a causative agent of bovine mastitis. Notably, LAB-derived metabolites demonstrated significant, strain-specific immunostimulatory activity. A comparative metabolomic analysis confirmed that each strain possessed a unique metabolic profile, providing a chemical basis for these various responses. The most pronounced effects were observed with metabolites from the isolated strain Enterococcus faecalis, which markedly increased NO production. Furthermore, these metabolites upregulated the expression of key inflammatory genes, e.g., iNOS, COX-2, TNF-α, and IL-6 and enhanced the protein levels of iNOS and COX-2. These findings suggest that LAB metabolites, particularly those from E. faecalis, may offer a novel therapeutic approach for enhancing immune defenses against mastitis-causing pathogens.