SUMMARY: A ssp. was isolated from goat's milk on the basis of its ability to inhibit the growth of . The antimicrobial effect was due to the presence in the culture medium of a compound, named mesentericin Y105, excreted by the Y105. The compound displayed known features of bacteriocins from lactic acid bacteria. It appeared as a proteinaceous molecule exhibiting a narrow inhibitory spectrum limited to genus . The apparent relative molecular mass, as indicated by activity detection after SDS-PAGE, was 2.5–3.0 kDa. The bacteriocin was purified to homogeneity by a simple three-step procedure: a crude supernatant obtained from an early-stationary-phase culture in a defined medium was subjected to affinity chromatography on a blue agarose column, followed by ultrafiltration through a 5 kDa cut-off membrane, and finally by reverse-phase HPLC on a C column. Microsequencing of the pure bacteriocin and of tryptic fragments showed that mesentericin Y105 is a 36 amino acid polypeptide whose primary structure is close to that of leucocin A-UAL 187, which contains an extra residue at the C-terminus and displays only two differences in the overlapping sequence. However, unlike leucocin A-UAL 187, mesentericin Y105 displayed a bactericidal mode of action.


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