First case of Streptococcus oligofermentans endocarditis determined based on sodA gene sequences after amplification directly from valvular samples

Elucidating the Role and Structure-Activity Relationships of the Streptococcus oligofermentans Competence-Stimulating Peptide

Streptococcus oligofermentans is an early colonizer of the oral microbiome with documented bactericidal activity against the oral pathogen Streptococcus mutans. S. oligofermentans has been observed to possess the typical comABCDE competence regulon found within most oral streptococci; however, the competence-stimulating peptide (CSP) responsible for QS activation and the regulatory role of the competence regulon is yet to be explored. Herein, we have both confirmed the identity of the S. oligofermentans CSP and utilized a wide range of phenotypic assays to characterize its regulatory role in competence, biofilm formation, and hydrogen peroxide formation. To determine the importance of each amino acid residue in CSP/ComD binding, we performed systematic replacement of amino acid residues within the S. oligofermentans CSP and developed a luciferase-based reporter system to assess the ability of these mutated analogues to modulate the competence regulon. Additionally, we performed CD analysis on mutated CSP analogues to determine the correlation between the peptide secondary structure and QS activation. To further explore S. oligofermentans' potential as a biotherapeutic against S. mutans infection, lead QS activators and inhibitors were used in interspecies competition assays to assess the effect of QS modulation on interactions between these two species. Lastly, we have documented a lack of S. oligofermentans-induced cytotoxicity, highlighting the potential of this native flora as a biotherapeutic with minimal health risks.

Racial Differences in the Oral Microbiome: Data from Low-Income Populations of African Ancestry and European Ancestry

Increasing evidence indicates the significant racial difference in gut, vaginal, and skin microbiomes. However, little is known regarding the racial difference in the oral microbiome. In this study, deep sequencing of 16S rRNA genes was utilized to assess the oral microbiome in mouth rinse samples of 1,058 African-Americans (AAs) and 558 European-Americans (EAs) from the Southern Community Cohort Study. Generally, AAs had a higher species richness than EAs, with P = 5.28 × 10-14 (Wilcoxon rank sum test) for Faith's phylogenetic diversity index. A significant difference in overall microbiome composition was observed between AAs and EAs, with P = 5.94 × 10-4 (MiRKAT) for the weighted UniFrac distance matrix. We also found 32 bacterial taxa showing a significant differential abundance or prevalence between the two racial groups at a Bonferroni-corrected P < 0.05 in linear or logistic regression analyses. Generally, AAs showed a higher abundance of Bacteroidetes and a lower abundance of Actinobacteria and Firmicutes Interestingly, four periodontal pathogens, Porphyromonas gingivalis, Prevotella intermedia, Treponema denticola, and Filifactor alocis, were more prevalent among AAs than among EAs, with Bonferroni-corrected P values of 5.23 × 10-6, 4.47 × 10-6, 1.08 × 10-3, and 4.49 × 10-5, respectively. In addition, all of these 32 taxa were significantly correlated with the percentage of genetic African ancestry. These findings call for research to understand how the racial difference in oral microbiome influences the health disparity.IMPORTANCE In this systemic investigation of racial differences in the oral microbiome using a large data set, we disclosed the significant differences in the oral microbial richness/evenness, as well as in the overall microbial composition, between African-Americans and European-Americans. We also found multiple oral bacterial taxa, including several preidentified oral pathogens, showing a significant different abundance or prevalence between African-Americans and European-Americans. Furthermore, these taxa were consistently found to be associated with the percentage of genetic African ancestry. Our findings warrant further research to understand how the racial difference in the oral microbiome influences the health disparity.

Oral microbiome and obesity in a large study of low-income and African-American populations

Few studies have evaluated the relationship of oral microbiome with obesity. We investigated the oral microbiome among 647 obese and 969 non-obese individuals from the Southern Community Cohort Study, through 16S rRNA gene sequencing in mouth rinse samples. We first investigated 16 taxa in two probiotic genera, Bifidobacterium and Lactobacillus. Among them, eight showed nominal associations with obesity (P < 0.05). Especially, Bifidobacterium (odds ratio [OR] = 0.67, 95% confidence interval [CI]:0.54, 0.83) and Bifidobacterium longum (OR = 0.57, 95% CI: 0.45, 0.73) were significantly associated with decreased obesity prevalence with false-discovery rate (FDR)-corrected P of 0.01 and 5.41 × 10-4, respectively. Multiple other bacterial taxa were also significantly associated with obesity prevalence at FDR-corrected P < 0.05. Among them, five in Firmicutes and two respectively in Actinobacteria and Proteobacteria were significantly associated with increased obesity prevalence. Significant associations with decreased obesity prevalence were observed for two taxa respectively in Actinobacteria and Firmicutes. Most of these taxa were associated with body mass index at study enrollment and weight gain during adulthood. Also, most of these associations were observed in both European- and African-Americans. Our findings indicate that multiple oral bacterial taxa, including several probiotic taxa, were significantly associated with obesity.

The Role of Macrophage Migration Inhibitory Factor in the Function of Intestinal Barrier

Macrophage migration inhibitory factor (MIF) is a multifunctional protein that is involved in the development of gut-related inflammation. To investigate the role of MIF in the function of the intestinal barrier, we have explored intestinal permeability and gut-associated immune response in MIF-deficient (MIF-KO) mice. The absence of MIF provoked impairment of tight and adherens epithelial junctions in the colon through the disturbance of E-cadherin, zonula occludens-1, occludin and claudin-2 expression, which lead to the increase of intestinal barrier permeability. In these circumstances the diversity and content of gut microbiota in MIF-KO mice was considerably different compared to wild type mice. This change in microbiota was accompanied by an increased intestinal IgA concentration and a higher production of pro-inflammatory cytokines TNF and IFN-γ in mesenteric lymph nodes of MIF-KO mice. The forced changes of microbiota executed by antibiotics prevented the "leakage" of the barrier in MIF-KO mice, probably through up-regulation of occludin expression and normalization of cellular pore diameters. In addition, cytokine secretion was normalized after the treatment with antibiotics. These results suggest that MIF participates in the maintenance of physiological microbiota diversity and immunosurveillance, which in turn enables the proper intestinal barrier function.

Phylogenomic and MALDI-TOF MS analysis of Streptococcus sinensis HKU4T reveals a distinct phylogenetic clade in the genus Streptococcus

Streptococcus sinensis is a recently discovered human pathogen isolated from blood cultures of patients with infective endocarditis. Its phylogenetic position, as well as those of its closely related species, remains inconclusive when single genes were used for phylogenetic analysis. For example, S. sinensis branched out from members of the anginosus, mitis, and sanguinis groups in the 16S ribosomal RNA gene phylogenetic tree, but it was clustered with members of the anginosus and sanguinis groups when groEL gene sequences used for analysis. In this study, we sequenced the draft genome of S. sinensis and used a polyphasic approach, including concatenated genes, whole genomes, and matrix-assisted laser desorption ionization-time of flight mass spectrometry to analyze the phylogeny of S. sinensis. The size of the S. sinensis draft genome is 2.06 Mb, with GC content of 42.2%. Phylogenetic analysis using 50 concatenated genes or whole genomes revealed that S. sinensis formed a distinct cluster with Streptococcus oligofermentans and Streptococcus cristatus, and these three streptococci were clustered with the “sanguinis group.” As for phylogenetic analysis using hierarchical cluster analysis of the mass spectra of streptococci, S. sinensis also formed a distinct cluster with S. oligofermentans and S. cristatus, but these three streptococci were clustered with the “mitis group.” On the basis of the findings, we propose a novel group, named “sinensis group,” to include S. sinensis, S. oligofermentans, and S. cristatus, in the Streptococcus genus. Our study also illustrates the power of phylogenomic analyses for resolving ambiguities in bacterial taxonomy.

Phylogenetic analysis supports horizontal gene transfer of L-amino acid oxidase gene in Streptococcus oligofermentans

Phylogenetic analysis of 10 amino acid sequences from 19 Streptococcus species showed that S. oligofermentans clustered within the mitis group. However, the l-amino acid oxidase (LAAO) of S. oligofermentans showed a different clustering pattern from the other proteins analyzed implicating horizontal gene transfer (HGT) in the origin of the S. oligofermentans LAAO gene. LAAO of S. oligofermentans is known to confer ability to compete with other oral cavity bacteria, most notably S. mutans; therefore, the HGT event may have been important in extending the ecological niche occupied by this species, consistent with those of other studies suggesting that HGT can play a key role in enabling bacterial species to occupy new ecological niches.

Streptococcus australis meningitis

We report a case of meningitis due to Streptococcus australis, a species of oral streptococcus. Accurate identification was performed by various molecular techniques.

Bacterial and host interactions of oral streptococci

The oral microbial flora comprises one of the most diverse human-associated biofilms. Its development is heavily influenced by oral streptococci, which are considered the main group of early colonizers. Their initial attachment determines the composition of later colonizers in the oral biofilm and impacts the health or disease status of the host. Thus, the role of streptococci in the development of oral diseases is best described in the context of bacterial ecology, which itself is further influenced by interactions with host epithelial cells, the immune system, and salivary components. The tractability of the oral biofilm makes it an excellent model system for studies of complex, biofilm-associated polymicrobial diseases. Using this system, numerous cooperative and antagonistic bacterial interactions have been demonstrated to occur within the community and with the host. In this review, several recent identified interactions are presented.