Purification, characterization, and identification of a novel bacteriocin produced by Lacticaseibacillus casei KLS1, and its antimicrobial mechanism against Staphylococcus aureus

Staphylococcus aureus (S. aureus) and its biofilm were recognized as one of the major threats to food safety and human health. Bacteriocins produced by Lacticaseibacillus species have been demonstrated to inhibit the growth of foodborne pathogenic bacteria and their biofilm formation. Herein, a novel bacteriocin KLS1 from Lacticaseibacillus casei KLS1 was extracted by ethyl acetate and purified using an AKTA Pure 25 protein chromatography purification system. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analyses revealed that the molecular mass of bacteriocin KLSI was 3786.91 Da and the amino acid sequence was DTSASIASNKSETNDLLKQIEAANTEVINLNKQID. Bacteriocin KLS1 was stable at pH 2.0∼6.0, sensitive to proteases, and showed excellent thermal stability. Furthermore, bacteriocin KLS1 exhibited broad-spectrum antimicrobial activity against both Gram-positive and Gram-negative bacteria, even fungi. The crystal violet staining assay indicated that bacteriocin KLS1 significantly reduced the relative percentage of S. aureus biofilm (P < 0.05). Meanwhile, bacteriocin KLS1 was found to significantly decrease the metabolic activity of S. aureus by Cell Counting Kit-8 assay (P < 0.05). In addition, scanning electron microscopy and confocal laser scanning microscope showed that bacteriocin KLS1 disrupted the structure of S. aureus biofilm and cell membrane integrity, leading to cell deformation and leakage of contents. These results suggested that bacteriocin KLS1 might have the potential to serve as a biological preservative in the food industry.