Abstract: Mutacin are bactericidal substances of proteinaceous natures produced by Streptococcus mutans. Lantibiotics are antibacterial substances containing posttranslationnally modified amino acids such as lanthionine. The present invention teaches a simple method of purifying mutacin B-Ny266 from Streptococcus mutans strain Ny266 to homogeneity. The present invention further teaches the primary amino acid sequence of mutacin B-Ny266 as well as its proposed modified structure. Further, the present invention teaches compositions comprising mutacin B-Ny266 as well as methods for the treatment and/or prophylaxy of bacterial infections comprising an administration of a suitable dose of composition comprising mutacin B-Ny266.