An inhibition factor from Streptococcus mutans strain C3603 (serotype c) was purified and isolated, and its properties indicated that it was a bacteriocin. Bacteriocin C3603 is a basic protein with a pI value of 10 and a molecular weight of 4,800. The activity of this bacteriocin was not affected by pH over a range of 1.0 to 12.0 or by storage at 100 degrees C for 10 min at pH 2.0 to 7.0 or storage at 121 degrees C for 15 min at pH 4.0. Pronase; papain, phospholipase C, trypsin, and alpha-amylase had no effect on the activity of the bacteriocin, whereas alpha-chymotrypsin and pancreatin were partially active against it. Bacteriocin activity was greater against certain S. mutans strains of serotypes b, c, e, and f than against certain S. mutans strains of serotypes a, d, and g. Bacteriocin C3603 was also effective against selected strains of S. sanguis, S. salivarius, S. bovis, S. faecium, S. lactis, Lactobacillus casei, L. plantarum, L. fermentum, Bifidobacterium bifidum, Bifidobacterium longum, Propionibacterium acnes, and Bacteroides melaninogenicus, but it was not effective against certain strains of Escherichia coli, Klebsiella pneumoniae, Corynebacterium parvum, and Candida albicans. The inhibition of S. mutans strains BHT and PS-14 by bacteriocin C3603 was found to be due to the bacteriocidal activity of the bacteriocin. When water or a diet containing bacteriocin C3603 was consumed by gnotobiotic and specific pathogen-free rats infected with S. mutans PS-14, the caries score was found to be significantly reduced.

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Soybean oligosaccharides(SOE) extracted from soybean whey serve as a growth-promoting agent for bifidobacteria.The effective components have been identified as the tri-and tetrasaccharide (SOR) fractions represented by raffinose (Raf) and stachyose (Sta). We therefore studied the digestibility of Raf and Sta. From the results of in vitro digestive experiments using the digestive enzymes, Raf and Sta were found to be almost indigestible.Raffinose and stachyose in the digestive tract of rats fed the conventional diet with 3.3% SOE were detected in the stomach and small intestine, but not in the large intestine or feces. Fecal excretion of Raf and Sta from germ-free mice was measured after one gastric intubation of SOR. Eighty to ninety percent of the Raf and Sta was recovered from the contents of the digestive tract and feces. These results suggest that Raf and Sta are neither degraded nor absorbed in the small intestine, but utilized efficiently by the microflora of the large intestine.

A bacteriocin from serotype c Streptococcus mutans strain C3603 was examined for its inhibitory effect on experimental dental caries in rats infected with S. mutans MT8148R (serotype c). Significant reduction in the incidence of dental caries was found only when bacteriocin was incorporated both in the drinking water and in the diet at a high concentration.However, caries reduction was not as great as expected and the addition of bacteriocin to drinking water alone had no effect on the recovery of S. mutans, plaque deposition or caries incidence. The bacteriocin activity must have been reduced in the oral cavity of rats, and the reasons were examined.Bacteriocin-resistant mutants were not detected and the bacteriocin was not inactivated by saliva.Whereas the bacteriocin did not kill the S. mutans cells grown in a sucrosecontaining medium, it completely killed the cells grown in a sucrose-free medium.