Screening of Bacteriocin-producing Lactic Acid Bacteria: Isolation and Purification of and Antibacterial Mechanism of Bacteriocin

A strain of lactic acid bacteria (LAB) with an inhibitory effect on Staphylococcus aureus was isolated from naturally fermented pickle. The strain was identified as Lactococcus lactis subsp. lactis and named NCU036018 by 16S rDNA gene sequence analysis and physiological and biochemical experiments. The antibacterial substance in the fermentation supernatant of NCU036018 was sensitive to trypsin, papain, protease K and α-chymotrypsin, but not to pepsine, lipase, amylase or catalase, and retained more than 70% and 90% of its activity at pH 2.0–10.0 and 50–100 ℃, respectively. Then, the antibacterial substance was separated and purified by successive steps of ammonium sulfate saltingout, ultrafiltration and cation exchange chromatography. The obtained bacteriocin was named lactococcin 036018, whose molecular mass and minimum inhibitory concentration (MIC) were 14.4-20 kDa and 0.50 mg/mL, respectively. Lactococcin 036018 could effectively reduce the biofilm formation rate of S. aureus, damage the morphology of the cell surface, reduce the permeability of the cell membrane and consequently inhibit or even killing the cells. The bacteriocin had a significant inhibitory effect on the growth of S. aureus in milk, thereby showing great promise as a food preservative.