Aims:  To assess the possibility that bifidobacteria compete with Porphyromonas gingivalis for their mutual growth factor vitamin K. This study also examined whether salivary Bifidobacterium species decrease vitamin K concentration in the growth medium. Methods and Results:  Sixty‐five strains of Bifidobacterium were obtained from 20 of 24 periodontally healthy subjects. Bifidobacterium dentium was most frequently detected in the saliva of subjects, followed by Bifidobacterium adolescentis, Bifidobacterium longum, and Bifidobacterium urinalis. The growth of most Bifidobacterium isolates, except that of B. urinalis, was stimulated by vitamin K. Moreover, the isolates were capable of decreasing vitamin K after incubation, which suggests that bifidobacteria compete with P. gingivalis for vitamin K. In a co‐culture, a representative strain –B. adolescentis S2‐1 – inhibited the growth of P. gingivalis if it was inoculated in the medium before P. gingivalis. Conclusions:  B. adolescentis S2‐1 decreased vitamin K concentration and inhibited the growth of P. gingivalis by possibly competing for the growth factor. Significance and Impact of the Study:  Salivary bifidobacteria may possess the potential to suppress the growth of P. gingivalis by reducing the growth factor(s) in the environment.

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A bifidogenic growth stimulator produced by Propionibacterium freudenreichii was purified, and its chemical structure was determined. We obtained 7.1 mg of a bifidogenic growth stimulator from 1738 g of lyophilized P. freudenreichii cells by silica gel column chromatography, Sephadex LH-20 column chromatography, and preparative HPLC. The mass of the bifidogenic growth stimulator was 217.037 (C11H7NO4) as determined by high resolution mass spectrometry. Various experimental analyses indicated that the chemical structure of the bifidogenic growth stimulator was 2-amino-3-carboxy-1,4-naphthoquinone.

We surveyed the distribution of salivary Lactobacillus and Bifidobacterium species in periodontitis patients and healthy subjects. Approximately 700 lactobacilli and 300 bifidobacterial isolates were obtained from 16 young, orally healthy subjects (mean age +/- standard deviation: 21.0+/-2.0 y), 16 periodontitis patients (51.6+/-13.8 y), and 14 well-maintained former periodontitis patients (60.2+/-9.6 y). Among eleven Lactobacillus species detected in saliva, L. salivarius, L. gasseri, and L. fermentum were prevalent, but no species was specifically associated with periodontal health. In contrast, of four Bifidobacterium species, B. adolescentis was specifically (P<0.05) prevalent in young healthy subjects compared with the other two groups. Furthermore, the bifidobacterial count of the well-maintained subjects was the highest (P<0.05) among the groups. These results suggest that bifidobacterial count and species might be associated with periodontal health status and/or age.

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