SUMMARY: Mutacin MT6223, a cell-free bacteriocin produced by MT6223, was purified by ammonium sulphate precipitation, chromatofocusing with PBE 94 and column chromatography on SP Sephadex C-25. The specific activity of the purified mutacin was increased 1950-fold with a recovery of 9·7%. The molecular mass of the purified mutacin preparation was estimated to be 6·5 kDa. The mutacin activity was stable from pH 2-7, and was resistant to treatment at 100 °C for 20 min. It was inactivated by papain or ficin digestion, and was partially inhibited by α-chymotrypsin. The mutacin was found to be active against strains of serotypes and of and the addition of purified mutacin MT6223 to growing cells of MT8148 resulted in a rapid inhibition of incorporation of [H]thymidine, [H]uracil or L-[H]glutamic acid into DNA, RNA or protein, respectively. Specific pathogen-free Fischer rats fed diet 2000 and infected with MT8148R showed significantly fewer caries and lower plaque scores when mutacin was administered through drinking water. The present study demonstrates that mutacin MT6223 inhibited the growth of mutans streptococci. Thus, mutacin MT6223 may be a candidate for use in dental caries prevention.


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