Production and characterization of a bacteriocin produced by Enterococcus faecium LR/6

A soil isolate of Lactic acid bacteria (LAB), strain LR/6 was identified as Enterococcus faecium on the basis of its morphological, biochemical, and 16S rDNA analysis. Strain LR/6 is a potential producer of an antimicrobial compound that followed the kinetic pattern typical of a primary metabolite synthesis and is released extracellularly. The antimicrobial action remained unaffected when treated with β-glycerophosphate and catalase suggesting that the activity is neither based on acid nor H2O2 production. This antimicrobial compound was highly stable over a wide range of pH (2.0 to 8.0), high temperature (boiling and autoclaving) and could be stored stably at a range of temperature (-20oC to 37oC) at least upto one year. The proteinaceous nature of the antimicrobial compound was ascertained by its sensitivity to many proteolytic enzymes confirming it to be a bacteriocin. Strain LR/6 bacteriocin was also insensitive to the presence of α-amylase, lipase, surfactants, organic solvents, and showed a bactericidal mode of action. Crude bacteriocin exhibited broad inhibition spectrum both against related as well as some foodborne pathogenic bacteria including Listeria monocytogenes. Tricine SDS-PAGE analysis and bacteriocin activity assay corresponded to a protein of an apparent molecular mass of ~6.0 kDa.