Antimicrobial Activity of Peptides Produced by Lactococcus lactis subsp. lactis on Swine Pathogens

SIMPLE SUMMARY: Antimicrobial peptides naturally produced by probiotic bacteria are used as alternatives to the long-term use of antibiotics against pathogenic bacteria. In the present study, we tested the effect of secreted compounds produced by the probiotic bacterium Lactococcus lactis subsp. lactis strain L2 on inhibiting the growth of pig pathogens in vitro. It was shown to be effective by bacteriostatic and bactericidal mechanisms in a strain-dependent manner, particularly against Gram-positive bacteria. The present analyses indicate that the molecules secreted in the cell-free supernatant responsible for this effect are of very low molecular weight, which may be responsible for this antimicrobial effect. Here we present potential beneficial effects of the use of probiotics in the control of pathogens in the pig industry. ABSTRACT: Swine production is of great importance worldwide and has huge economic and commercial impact. Due to problems with bacterial infection, the use of antimicrobials has increased in the last decades, particularly in Latin America and Asia. This has led to concerns about antimicrobial resistance, which poses risks to human health and the environment. The use of probiotic organisms has been proposed as an alternative to this use, as these beneficial bacteria can produce antimicrobial peptides, such as bacteriocins, which allow the induction of inhibitory effects against pathogenic microorganisms. Among probiotics, some bacteria stand out with the inhibition of animal pathogens. The bacteriocin-like inhibitory substances (BLISs) of Lactococcus lactis subsp. lactis strain L2, present in its cell-free supernatant, were tested against pathogenic strains isolated from pig samples, such as Escherichia coli, Salmonella enterica, Streptococcus suis, Streptococcus dysgalactiae, Staphylococcus hyicus, and Enterococcus faecalis. Compounds secreted by L. lactis L2 have been shown to inhibit the growth of some pathogenic species, particularly Gram-positive bacteria, with S. suis being the most prominent. Antimicrobial peptides with a molecular size of 500–1160 Daltons were isolated from BLISs. The results highlight the potential of L. lactis BLISs and its peptides as natural antimicrobials for use in the food industry and to reduce the use of growth promoters in animal production.