Characterization and mode of action of a purified bacteriocin from the oral bacterium Streptococcus mutans RM-10

The purified bacteriocin was sensitive to proteolytic enzymes such as trypsin, alpha-chymotrypsin and pronase, but resistant to papain and pepsin. Lowering the pH of the bacteriocin caused precipitation, and the Abs280 of the supernatant reached a minimum at pH 3.6, suggesting that this is the isoelectric point. Such a pH value coincides with minimum bacteriocin activity. The effect of the bacteriocin was bactericidal rather than bacteriolytic and concentration dependent. Treatment of Streptococcus faecalis ODU with Rm-10 bacteriocin led rapidly to the cessation of biosynthesis of macromolecules, DNA, RNA and protein. Electron microscopy showed bacteriocin fibres attached in aggregated bundles to target cells; after ultra-sonication or detergent treatment they were individually attached to the cell surface and, at the same time, the apparent bacteriocin activity had doubled. Bacteriocin activity was not altered by filter-sterilized saliva components. Oral rinsing with Rm-10 bacteriocin reduced the number of viable salivary bacteria after 20 min, suggesting a possible therapeutic use for Rm-10 bacteriocin.