Characterization of enterocin-like substances produced by two strains of Enterococci isolated from ewe's and goat's milks

Raw milk is a source of new strains of bacteriocin-producing lactic acid bacteria (LAB) with the potential to inhibit undesirable microorganisms. The aim of this work was to detect the bacteriocin-producing LAB from raw ewe's and goat's milks and characterize the isolated bacteriocins. A total of 100 samples of ewe's and goat's milks were screened for bacteriocin-producing lactic acid bacteria. Two strains were selected and identified phenotypically to genus level. The serums of cultures of the selected strains were treated with various enzymes to detrmine the nature of their antimicrobial substances. The inhibition potential of the substances was investigated by agar well diffusion assay and their stability at different temperatures and pH's were determined. The antimicrobial substances were partially purified by ammonium sulphate and poly-ethylene gltcol (PEG) and the titer determined. In addition, their molcular weights were determined by SDS-PAGE analysis and their resistance estimated during storage at 4 °C. The two strains of Enterococcus, Le40 and Le50, exhibited a broad antimicrobial activity in several replicates. The sensivity of the inhibitory substances to proteolytic enzymes confirmed the production of enterocin-like substances (ELS) by these strains. Listeria monocytogenes and Staphylococcus aureus were inhibited by the ELSs. The ELSs were both stable at a wide pH range (pH 3-10) and the one isolated from Le50 was resistant to heat. Partial purification of both the ELSs increased their activity and titer. Their molcular weights were between 24 and 29 KD. Finally, the ELS's activity was maintained during storage at 4 °C for 28 days. Considering the desirable antimicrobial characteristics and biochemical properties of the isolated ELSs, further studies to explore the possibility of using them as biopreservatives in food processing is recommended.