Mastitis is one of the most important and multi-factorial diseases affecting dairy cows. This study was conducted to evaluate the effect of postbiotics secreted by lactic acid bacteria on mastitis. Within this aim, a total of 10 raw milk samples of healthy dairy cows were processed for the isolation of microbiota-derived bacteria. Following the isolation protocol, 24 isolates showing phenotypic characters similar to Lactobacillus species on specific MRS agar were selected and screened for their antibacterial activity against important mastitis-causing pathogens using the agar well diffusion method. According to the screening of the isolates, only one strain was found effective against all tested pathogens and selected for further assays. The isolate that exhibited a remarkable inhibitory effect was then identified as Lactobacillus sakei by 16S rRNA sequence analysis. The minimum inhibitory concentration of the postbiotics secreted by L. sakei into the culture medium was defined between the range of 40–50 mg/L. The antibacterial activity was also determined to be an acid-dependent effect, and HPLC analysis confirmed the presence of lactic acid (21.42 mg/mL) as the most common acid in the postbiotics. Among the 37 fatty acids, only oleic acid, palmitic acid, and stearic acid were detected. In addition to its antibacterial activity, postbiotics significantly reduced the biofilm formation of pathogens following the co-incubation, pre-treatment, and eradication assays, confirmed by confocal-laser and scanning electron microscopy. In conclusion, postbiotics with antibacterial and antibiofilm activity against important mastitis-causing pathogens can be used as a promising and natural agent in the prevention of mastitis.

Previous studies have indicated that the exopolysaccharides of lactic acid bacteria exhibit antibiofilm activity against non-oral bacteria by preventing their initial adhesion to surfaces and by downregulating the expression of genes responsible for their biofilm formation. The aims of this study were to (1) characterize the exopolysaccharides (EPSs) of Lactobacillus plantarum EIR/IF-1 postbiotics, (2) test their antibiofilm effect on dual biofilms, and (3) evaluate their bacterial auto-aggregation, co-aggregation, and hydrocarbon-binding inhibitory activity. The EPSs were characterized by FTIR, HPLC, and thermogravimetric analysis. Bacterial auto- and co-aggregation were tested by Kolenbrander’s method and hydrocarbon binding was tested by Rosenberg’s method. Dual biofilms were formed by culturing Fusobacterium nucleatum ATCC 25586 with one of the following bacteria: Prevotella denticola ATCC 33185, P. denticola AHN 33266, Porphyromonas gingivalis ATCC 33277, P. gingivalis AHN 24155, and Filifactor alocis ATCC 35896. The EPSs contained fractions with different molecular weights (51 and 841 kDa) and monosaccharides of glucose, galactose, and fructose. The EPSs showed antibiofilm activity in all the biofilm models tested. The EPSs may have inhibited bacterial aggregation and binding to hydrocarbons by reducing bacterial hydrophobicity. In conclusion, the EPSs of L. plantarum EIR/IF-1, which consists of two major fractions, exhibited antibiofilm activity against oral bacteria, which can be explained by the inhibitory effect of EPSs on the auto-aggregation and co-aggregation of bacteria and their binding to hydrocarbons.