Purification of novel bacteriocin produced by Lactobacillus coryniformis MXJ 32 for inhibiting bacterial foodborne pathogens including antibiotic-resistant microorganisms

Bacteriocins produced by LAB comprise a variety of antimicrobial proteins or peptides which can be used as food biopreservatives and/or possible antibiotic alternatives. Bacteriocin-producing Lactobacillus coryniformis MXJ 32, which was identified based on its 16S rRNA gene sequence, was isolated from a traditional fermented vegetable (Jiangshui Cai) of Xixiang county, Shaanxi province, China. Thereafter bacteriocin (designated as lactocin MXJ 32A) produced by L. coryniformis MXJ 32 was purified by ammonium sulfate precipitation, dialysis and ion exchange chromatography. The molecular mass of lactocin MXJ 32A was 3520 Da determined by LC-ESI/MS and the N-terminal sequence of lactocin MXJ 32A was NH2-GEPGPMGPAGAD. Lactocin MXJ 32A had a broad antimicrobial spectrum including many Gram-positive and Gram-negative foodborne pathogens, in which even some antibiotic-resistant foodborne pathogenic strains could also be inhibited. The MIC of lactocin MXJ 32A for Staphylococcus aureus and Escherichia coli was 10 mg/mL. Lactocin MXJ 32A showed good pH-stability and heat stability and was sensitive to proteolytic enzymes. It was shown by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) that the possible mode of action of lactocin MXJ 32A was pore formation of the cytoplasmic membrane of target cells.