Streptococcus faecium-derived antibacterial substance antagonistic to Bifidobacteria.

An antagonistic strain of Streptococcus faecium was isolated from human feces, and it displayed a marked inhibition of bifidobacteria on agar plates. In liquid culture this isolate produced an antibacterial substance that can be partially purified by ammonium sulfate precipitation followed by gel filtration and ion-exchange chromatography. Its activity was assayed by the inhibition of growth of Bifidobacterium longum. The substance was sensitive to digestion by proteolytic enzymes and alpha-amylase, but was resistant to treatment with 6 M urea, dithiothreitol, 2-mercaptoethanol, ethyl ether, chloroform, and lysozyme. It was also stable to heating at 100 degrees C for 60 min. Its molecular weight was estimated to be about 50,000 by gel filtration.