Preliminary results of antimicrobial activity of bacteriocins secreted by lactic acid bacteria against mastitis pathogens

In the last thirty years antimicrobial peptides known as bacteriocins, that are secreted by strains of lactic acid bacteria (LAB), have been studied mainly in the dairy industry, for their antibacterial activity. Recently, their prophylactic and therapeutic efficacy against bacteria agents of dairy cow mastitis has been also demonstrated. Few studies have been performed about the efficacy of different bacteriocins in clinical and subclinical mastitis and as teat sealant. We tested 18 LAB strains for production of antibacterial metabolites after different culture times and with different extraction methods. Minimum inhibitory concentration (MIC) test of culture supernatants was performed using the microdilution broth method. Two strains (SC20 and LL11) showed antibacterial activity against different mastitis pathogens (S. agalactiae, S. uberis, S. aureus, E. faecalis and L. monocytogenes), but the efficacy changed in relation to the bacteria tested. The highest MIC values were achieved using LL11, after extraction of bacteriocins at ph 2. The most sensitive strains were S. agalactiae, which were inhibited at a dilution of 1:380, while all the other isolates showed variable sensitivity. Our results represent the starting point for further studies aimed to the development of non-antibiotic formulations as prophylactic and therapeutic tools in dairy cow mastitis. Antibacterial substances produced by LAB have the potential to reduce the use of antibiotics in the dairy farm, with a consequent reduction of the risk of residues for the consumer.