Kenichi Hojo

Bacterial Interactions in Dental Biofilm Development

Recent analyses with ribosomal RNA-based technologies have revealed the diversity of bacterial populations within dental biofilms, and have highlighted their important contributions to oral health and disease. Dental biofilms are exceedingly complex and multispecies ecosystems, where oral bacteria interact cooperatively or competitively with other members. Bacterial interactions that influence dental biofilm communities include various different mechanisms. During the early stage of biofilm formation, it is known that planktonic bacterial cells directly attach to surfaces of the oral cavity or indirectly bind to other bacterial cells that have already colonized. Adherence through co-aggregation may be critical for the temporary retention of bacteria on dental surfaces, and may facilitate eventual bacterial colonization. It is likely that metabolic communication, genetic exchange, production of inhibitory factors (e.g., bacteriocins, hydrogen peroxide, etc.), and quorum-sensing are pivotal regulatory factors that determine the bacterial composition and/or metabolism. Since each bacterium can easily access a neighboring bacterial cell and its metabolites, genetic exchanges and metabolic communication may occur frequently in dental biofilms. Quorum-sensing is defined as gene regulation in response to cell density, which influences various functions, e.g., virulence and bacteriocin production. In this review, we discuss these important interactions among oral bacteria within the dental biofilm communities.

Isolation and Identification of a New Bifidogenic Growth Stimulator Produced by Propionibacterium freudenreichii ET-3

We have found a new growth stimulator for bifidobacteria in the culture broth of Propionibacterium freudenreichii ET-3. The bifidogenic growth stimulator (BGS) was purified by Diaion HP-20 column chromatography and preparative HPLC. Spectroscopic methods including 1H-NMR, UV, and LC-ESI-MS experiments indicated that the chemical structure of the bifidogenic growth stimulator was 1,4-dihydroxy-2-naphthoic acid (DHNA). Approximately 10 mg/L of DHNA was found to be produced in the culture broth of P. freudenreichii ET-3.

Distribution of Salivary Lactobacillus and Bifidobacterium Species in Periodontal Health and Disease

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.

Interactions between salivary Bifidobacterium adolescentis and other oral bacteria : in vitro coaggregation and coadhesion assays

Coaggregation assays were performed to investigate interactions between oral Bifidobacterium adolescentis and other oral bacterial species. Bifidobacterium adolescentis OLB6410 isolated from the saliva of healthy humans did not coaggregate with Actinomyces naeslundii JCM8350, Streptococcus mitis OLS3293, Streptococcus sanguinis JCM5708, Veillonella parvula ATCC17745 or Porphyromonas gingivalis OB7124, but it did coaggregate with Fusobacterium nucleatum JCM8532. Subsequent examination of biofilm formation on saliva-coated hydroxyapatite discs using FISH revealed that B. adolescentis OLB6410 could not directly adhere to the coated discs. It did, however, adhere to biofilms of A. naeslundii, V. parvula, and F. nucleatum, although it did not coaggregate with A. naeslundii nor with V. parvula. These results suggest that the adhesion of B. adolescentis to tooth surfaces is mediated by other oral bacteria. Heat- or proteinase K-treated F. nucleatum could not coaggregate with B. adolescentis. Similarly, the coaggregation and coadhesion of proteinase K-treated B. adolescentis were strongly inhibited. It is therefore probable that proteinaceous factors on the cellular surface of B. adolescentis and F. nucleatum are involved in their interaction. The data presented in this study add to our understanding of bifidobacterial colonization in the human oral cavity.

Predominant Bacteria Recovered from a Periodontitis Site in a Hamster Model Raised by Silk-Ligature with Prophyromonas gingivalis Infection

We isolated oral bacteria that coexisted with Porphyromonas gingivalis in a hamster periodontitis model. As predominant bacteria in the periodontitis site, Collinsella-reltaed strains, Eubacterium-reltaed strains, Streptococcus suis-related strains, and Veillonella parvula-reltaed strains were detected. In addition, Actinomyces, Bacteroides, and P. gingivalis were also isolated predominantly. The results suggest that the bacterial composition of the periodontitis site in hamsters is complex, as in human periodontitis.

Abnormal fecal Lactobacillus flora and vitamin B12 deficiency in a patient with short bowel syndrome.

Lactobacillus overgrowth has been reported in patients with short bowel syndrome (SBS) (1–4). We previously reported D-lactic acidosis that Lactobacillus overgrowth caused in a male SBS patient (5). He had severe anemia related to vitamin B12 deficiency 9 years later. It has been generally accepted that B12 deficiency in SBS patients results from the inadequate absorption of B12 and/or the bacteria–host competition for uptake of B12 (6). In the present study, we suspected the recurrence of Lactobacillus overgrowth as a possible cause, because some lactobacilli require B12 for growth. Therefore, we analyzed the fecal flora and the B12 auxotrophy of Lactobacillus isolates.

Antibacterial Activity of Sodium Citrate against Oral Bacteria Isolated from Human Tongue Dorsum

Antibacterial activity of sodium citrate against tongue bacteria, especially hydrogen-sulfide (H2S) producers, was examined. Based on 16s rDNA partial sequences analysis, 691 isolates from 6 subjects were identified. In the present study, Prevotella histicola, P. melaninogenica, Veillonella atypica and V. dispar/V. parvula were detected as predominant H2S producing bacteria. Antibacterial assay showed that sodium citrate inhibited the growth of the representative strains of H2S producers at low concentrations although it similarly inhibited that of commensal bacteria, viz., Streptococcus parasanguinis and S. salivarius. When the effects of several pH conditions on antibacterial activity of sodium citrate against P. melaninogenica JCM6325T were examined, the activity was effective under neutral pH as well as under acidic conditions.

Potential Antagonistic Activity of Bifidobacterium adolescentis against Porphyromonas gingivalis in a Hamster Periodontitis Model

The antagonistic activity of Bifidobacterium adolescentis against Porphyromonas gingivalis was investigated in a hamster periodontitis model. Experimental periodontitis was induced by a silk-suture that was placed around the first molar of the lower jaw and inoculation with P. gingivalis. Real-time PCR was applied for the enumeration of P. gingivalis. Three B. adolescentis strains were individually used to inoculate the oral cavity for five weeks. In this study, B. adolescentis OLB6410 and KH96 were recovered from the oral cavity of hamsters and they seemed to weakly inhibit (p<0.1) the growth of P. gingivalis as compared with the control group. In contrast, OLB6398 did not affect the growth of P. gingivalis. Although the results did not reach significance, we propose a hypothesis whereby colonizing B. adolescentis potentially competes with P. gingivalis. This study sheds new light on the development of probiotics for the prevention of periodontal disease.

Anti-Fatigue Effects of Yogurt Fermented with Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1 in Healthy People Suffering from Summer Heat Fatigue: A Randomized, Double-Blind, Placebo-Controlled Trial

Fatigue caused by summer heat is a typical indefinite complaint along with anorexia, loss of sleep, stress, lack of motivation and, in some cases, catching a cold. Yogurt fermented with Lactobacillus delbrueckii subsp. bulgaricus OLL1073R-1 has been shown to stimulate the immune system and reduce the risk of catching colds. Here, we conducted a randomized, double-blinded, placebo-controlled trial to investigate whether ingesting this yogurt could ameliorate summer heat fatigue in 49 healthy males (median age 40.0 ± 6.0 years; 30–49 years) who felt fatigued every summer. Fatigue was evaluated by visual analogue scales (VAS) and the balance of sympathetic/parasympathetic nervous systems. After 12 weeks of ingestion in early autumn, the VAS fatigue scores in the yogurt group were lower than those of the placebo group. These results indicate that yogurt fermented with L. bulgaricus OLL1073R-1 can ameliorate summer heat fatigue lasting up to early autumn.