Bovine mastitis is one of the most significant causes of economic losses for the dairy industry. On the other hand, public health authorities advise prudent use of antibiotics because they could promote bacterial resistance and leave residues in food chain. The dairy industry could benefit from the development of safe antimicrobial agents and bacteriocins could be attractive alternatives to antibiotics. Due to the safety of Lactic acid bacteria (LAB), their bacteriocins have the potential to be used as antimicrobials in veterinary clinical application. We analyzed the efficacy of antibacterial substances produced by bacteriocinogenic Lactococcus lactis subsp. lactis strains against contagious and environmental mastitis pathogens. Thereafter, we investigated how lactococcal strains or their bacteriocins could influence mammary gland innate immune response in vitro. Out of 65 LAB strains tested, 3 were active against mastitis pathogens: 2 strains produced Nisin, one Lacticin 481 and in addition a novel molecule with likely antibacterial activity. To analyze the immune response of mammary epithelial cells when stimulated with lactococcal strains or bacteriocins, a stabilized epithelial cell line, BME-UV1, was used. Both lactococcal live cultures and their antibacterial products were shown to modulate the non-specific immune response of BME-UV1 cells: Lysozyme and N-acetil-\u3b2-D-glucosaminidase excretion were overall enhanced by bacteriocins and live-culture treatments, while intracellular amounts were unaffected by treatments. Proinflammatory cytokine expression of treated BME-UV1 was similar to that observed in control cells, except for Lactococcus lactis subsp. lactis SL153. Such strain induced a significant reduction of TNF\u3b1 transcriptional level.
The stimulation of enzyme secretion due to the administration of lactococci or of their antibacterial products, with potential enhancement of pathogens cleaning, can be of interest for the prevention of intra mammary infections. In addition, Lactococcus lactis subsp. lactis SL153 strain could be advantageous for its potential anti-inflammatory properties and could be of interest for the development of intra-mammary probiotic treatments
