The Regulatory Role of the Oral Commensal Streptococcus mitis on Human Monocytes

Oral streptococci: modulators of health and disease

Streptococci are primary colonizers of the oral cavity where they are ubiquitously present and an integral part of the commensal oral biofilm microflora. The role oral streptococci play in the interaction with the host is ambivalent. On the one hand, they function as gatekeepers of homeostasis and are a prerequisite for the maintenance of oral health - they shape the oral microbiota, modulate the immune system to enable bacterial survival, and antagonize pathogenic species. On the other hand, also recognized pathogens, such as oral Streptococcus mutans and Streptococcus sobrinus, which trigger the onset of dental caries belong to the genus Streptococcus. In the context of periodontitis, oral streptococci as excellent initial biofilm formers have an accessory function, enabling late biofilm colonizers to inhabit gingival pockets and cause disease. The pathogenic potential of oral streptococci fully unfolds when their dissemination into the bloodstream occurs; streptococcal infection can cause extra-oral diseases, such as infective endocarditis and hemorrhagic stroke. In this review, the taxonomic diversity of oral streptococci, their role and prevalence in the oral cavity and their contribution to oral health and disease will be discussed, focusing on the virulence factors these species employ for interactions at the host interface.

Detailed Characterization of the Lung-Gut Microbiome Axis Reveals the Link between PD-L1 and the Microbiome in Non-Small-Cell Lung Cancer Patients

Next-generation sequencing technologies have started a new era of respiratory tract research in recent years. Alterations in the respiratory microbiome between healthy and malignant conditions have been revealed. However, the composition of the microbiome varies among studies, even in similar medical conditions. Also, there is a lack of complete knowledge about lung-gut microbiome interactions in lung cancer patients. The aim of this study was to explore the lung-gut axis in non-small-cell lung cancer (NSCLC) patients and the associations between lung-gut axis microbiota and clinical parameters (CRP, NLR, LPS, CD8, and PD-L1). Lung tissue and fecal samples were used for bacterial 16S rRNA sequencing. The results revealed, for the first time, that the bacterial richness in lung tumor tissue gradually decreased with an increase in the level of PD-L1 expression (p < 0.05). An analysis of β-diversity indicated a significant positive correlation between the genera Romboutsia and Alistipes in both the lung tumor biopsies and stool samples from NSCLC patients (p < 0.05). Survival analysis showed that NSCLC patients with higher bacterial richness in their stool samples had prolonged overall survival (HR: 2.06, 95% CI: 1.025-4.17, p = 0.0426).

Oral microbiota and oral squamous cell carcinoma: a review of their relation and carcinogenic mechanisms

Oral Squamous Cell Carcinoma (OSCC) is the most common type of head and neck cancer worldwide. Emerging research suggests a strong association between OSCC and the oral microbiota, a diverse community of bacteria, fungi, viruses, and archaea. Pathogenic bacteria, in particular Porphyromonas gingivalis and Fusobacterium nucleatum, have been closely linked to OSCC. Moreover, certain oral fungi, such as Candida albicans, and viruses, like the human papillomavirus, have also been implicated in OSCC. Despite these findings, the precise mechanisms through which the oral microbiota influences OSCC development remain unclear and necessitate further research. This paper provides a comprehensive overview of the oral microbiota and its relationship with OSCC and discusses potential carcinogenic pathways that the oral microbiota may activate or modulate are also discussed.

Modeling periodontal host-microbe interactions using vascularized gingival connective tissue equivalents

Gingival connective tissue and its vasculature play a crucial role in the host's immune response against the periodontal microbiome and serve as a bridge between the oral and systemic environments. However, there is a lack of representative models that mimic the complex features of vascularized gingival connective tissue and its interaction with the periodontal microbiome, hindering our understanding of periodontal health and disease. Towards this pursuit, we present the characterization of vascularized gingival connective tissue equivalents (CTEs) as a model to study the interactions between oral biofilm colonizers and gingival tissues in healthy and diseased states. Whole-mount immunolabeling and label-free confocal reflectance microscopy of human fibrin-based matrix embedded with gingival fibroblasts and microvascular endothelial cells demonstrated the generation of bi-cellular vascularized gingival CTEs. Next, we investigated the response of the vascularized gingival CTEs to early, intermediate, and late oral biofilm colonizers. Despite colonization, the early colonizers did not elicit any significant change in the production of the cytokines and chemokines by the CTEs representative of the commensal and homeostatic state. In contrast, intermediate and late colonizers representing a transition to a diseased state exhibited connective tissue and vascular invasion, and elicited a differential immune response accompanied by increased monocyte migration. The culture supernatants produced by the vascularized gingival CTEs in response to early and intermediate colonizers polarized macrophages towards an immunomodulatory M2-like phenotype which activates and protects the host, while the late colonizers polarized towards a pro-inflammatory M1-like phenotype. Lastly,in silicoanalysis showed a high strength of associations between the proteins and transcripts investigated with periodontitis and vascular diseases. In conclusion, the vascularized gingival CTEs provide a biomimeticin vitroplatform to study host-microbiome interactions and innate immune response in periodontal health and diseased states, which potentially paves the way toward the development and assessment of novel periodontal therapeutics.

Group B streptococci infection model shows decreased regulatory capacity of cord blood cells

BACKGROUND

Sepsis is one of the leading causes of morbidity and mortality in the neonatal period. Compared to adults, neonates are more susceptible to infections, especially to systemic infections with Group B Streptococcus (GBS). Furthermore, neonates show defects in terminating inflammation. The immunological causes for the increased susceptibility to infection and the prolonged inflammatory response are still incompletely understood.

METHODS

In the present study, we aimed to investigate the reaction of cord blood mononuclear cells (MNC) to stimulation with GBS in comparison to that of MNC from adult blood with focus on the proliferative response in an in vitro infection model with heat-inactivated GBS.

RESULTS

We demonstrate that after stimulation with GBS the proliferation of T cells from adult blood strongly decreased, while the proliferation of cord blood T cells remained unchanged. This effect could be traced back to a transformation of adult monocytes, but not cord blood monocytes, to a suppressive phenotype with increased expression of the co-inhibitory molecule programmed death ligand 1 (PD-L1).

CONCLUSIONS

These results point towards an increased inflammatory capacity of neonatal MNC after stimulation with GBS. Targeting the prolonged inflammatory response of neonatal immune cells may be a strategy to prevent complications of neonatal infections.

IMPACT

Neonatal sepsis often leads to post-inflammatory complications. Causes for sustained inflammation in neonates are incompletely understood. We show that cord blood T cells exhibited increased proliferative capacity after stimulation with group B streptococci (GBS) in comparison to adult T cells. Adult monocytes but not cord blood monocytes acquired suppressive activity and expressed increased levels of PD-L1 after GBS stimulation. Increased proliferative capacity of neonatal T cells and decreased suppressive activity of neonatal monocytes during GBS infection may contribute to prolonged inflammation and development of post-inflammatory diseases in newborns.

Core Microbiota in Central Lung Cancer With Streptococcal Enrichment as a Possible Diagnostic Marker

BACKGROUND

Dysbiosis in lung cancer has been underexplored. The aim of this study was to define the bacterial and fungal microbiota of the bronchi in central lung cancer and to compare it with that of the oral and intestinal compartments.

METHODS

Twenty-five patients with central lung cancer and sixteen controls without antimicrobial intake during the previous month were recruited. Bacterial and fungal distribution was determined by massive sequencing of bronchial biopsies and saliva and faecal samples. Complex computational analysis was performed to define the core lung microbiota.

RESULTS

Affected and contralateral bronchi of patients have almost identical microbiota dominated by Streptococcus, whereas Pseudomonas was the dominant genera in controls. Oral and pulmonary ecosystems were significantly more similar in patients, probably due to microaspirations. Streptococcal abundance in the bronchi differentiated patients from controls according to a ROC curve analysis (90.9% sensitivity, 83.3% specificity, AUC=0.897). The saliva of patients characteristically showed a greater abundance of Streptococcus, Rothia, Gemella and Lactobacillus. The mycobiome of controls (Candida) was significantly different from that of patients (Malassezia). Cancer patients' bronchial mycobiome was similar to their saliva, but different from their contralateral bronchi.

CONCLUSIONS

The central lung cancer microbiome shows high levels of Streptococcus, and differs significantly in its composition from that of control subjects. Changes are not restricted to tumour tissue, and seem to be the consequence of microaspirations from the oral cavity. These findings could be useful in the screening and even diagnosis of this disease.

Comparison of Gut Microbiota Between Infants with Atopic Dermatitis and Healthy Controls in Guangzhou, China

Purpose

Evidence on the role of the gut microbiota in atopic dermatitis is inconsistent as human intestinal microbiota is influenced by geography. This cross-sectional study therefore aimed to compare differences in the gut microbiota of infants with atopic dermatitis and healthy infants in Guangzhou, China, by analyzing their stool.

Patients and Methods

The composition of the intestinal microbiota was analyzed from the stool samples of 20 infants with atopic dermatitis (AD group) and 25 healthy infants (non-AD group) (1-6 months old), using full-length 16S rRNA gene sequencing. The Wilcoxon test was used to analyze the relative abundance of bacteria by phylum, family, genus, and species between groups; microbial community richness and diversity were compared between the two groups.

Results

There were no significant differences in the microbial community richness and diversity between the two groups. At the phylum level, 11 bacterial phyla were found; most sequences belonged to one of the three dominant bacterial phyla - Firmicutes, Proteobacteria, and Bacteroidetes. The top 10 microbes at the phylum, family, and genus levels showed no significant changes in their composition within the gut microbiota between the AD and non-AD groups. A decrease in the ratio of the Streptococcus genus was found in atopic dermatitis group when compared with healthy controls (p=0.048).

Conclusion

A decrease in the abundance of Streptococcus was found in children with AD. The role of Streptococcus in the development of AD needs to be confirmed in a large cohort study.

Immunomodulatory streptococci that inhibit CXCL8 secretion and NFκB activation are common members of the oral microbiota

Introduction

Oral tissues are generally homeostatic despite exposure to many potential inflammatory agents including the resident microbiota. This requires the balancing of inflammation by regulatory mechanisms and/or anti-inflammatory commensal bacteria. Thus, the levels of anti-inflammatory commensal bacteria in resident populations may be critical in maintaining this homeostatic balance.

Hypothesis/Gap Statement

The incidence of immunosuppressive streptococci in the oral cavity is not well established. Determining the proportion of these organisms and the mechanisms involved may help to understand host-microbe homeostasis and inform development of probiotics or prebiotics in the maintenance of oral health.

Aim

To determine the incidence and potential modes of action of immunosuppressive capacity in resident oral streptococci.

Methodology

Supragingival plaque was collected from five healthy participants and supragingival and subgingival plaque from five with gingivitis. Twenty streptococci from each sample were co-cultured with epithelial cells±flagellin or LL-37. CXCL8 secretion was detected by ELISA, induction of cytotoxicity in human epithelial cells by lactate dehydrogenase release and NFκB-activation using a reporter cell line. Bacterial identification was achieved through partial 16S rRNA gene sequencing and next-generation sequencing.

Results

CXCL8 secretion was inhibited by 94/300 isolates. Immunosuppressive isolates were detected in supragingival plaque from healthy (4/5) and gingivitis (4/5) samples, and in 2/5 subgingival (gingivitis) plaque samples. Most were Streptococcus mitis/oralis. Seventeen representative immunosuppressive isolates all inhibited NFκB activation. The immunosuppressive mechanism was strain specific, often mediated by ultra-violet light-labile factors, whilst bacterial viability was essential in certain species.

Conclusion

Many streptococci isolated from plaque suppressed epithelial cell CXCL8 secretion, via inhibition of NFκB. This phenomenon may play an important role in oral host-microbe homeostasis.

Differential influence of Streptococcus mitis on host response to metals in reconstructed human skin and oral mucosa

BACKGROUND

Skin and oral mucosa are continuously exposed to potential metal sensitizers while hosting abundant microbes, which may influence the host response to sensitizers. This host response may also be influenced by the route of exposure that is skin or oral mucosa, due to their different immune properties.

OBJECTIVE

Determine how commensal Streptococcus mitis influences the host response to nickel sulfate (sensitizer) and titanium(IV) bis(ammonium lactato)dihydroxide (questionable sensitizer) in reconstructed human skin (RHS) and gingiva (RHG).

METHODS

RHS/RHG was exposed to nickel or titanium, in the presence or absence of S. mitis for 24 hours. Histology, cytokine secretion, and Toll-like receptors (TLRs) expression were assessed.

RESULTS

S. mitis increased interleukin (IL)-6, CXCL8, CCL2, CCL5, and CCL20 secretion in RHS but not in RHG; co-application with nickel further increased cytokine secretion. In contrast, titanium suppressed S. mitis-induced cytokine secretion in RHS and had no influence on RHG. S. mitis and metals differentially regulated TLR1 and TLR4 in RHS, and predominantly TLR4 in RHG.

CONCLUSION

Co-exposure of S. mitis and nickel resulted in a more potent innate immune response in RHS than in RHG, whereas titanium remained inert. These results indicate the important influence of commensal microbes and the route of exposure on the host's response to metals.

Porphyromonas gingivalis-Induced NLRP3 Inflammasome Activation and Its Downstream Interleukin-1β Release Depend on Caspase-4

Background: Oral commensals contribute to microbe-host symbiosis in periodontal homeostasis, and Porphyromonas gingivalis (P. gingivalis) as the keystone pathogen critically accounts for the shift of symbiosis to dysbiosis and periodontal destruction. Nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family pyrin domain containing 3 (NLRP3) inflammasome-mediated interleukin-1β (IL-1β) is significantly involved in periodontal diseases, and notably P. gingivalis enables to modulate the induction and expression of NLRP3. Whereas, the exact mechanism by which NLRP3 inflammasome is regulated in response to commensal and pathogenic bacteria remains unclear.

Methods: To examine the expression of IL-1β and NLRPs inflammasome in tissues with severe chronic periodontitis, and further investigate how Caspase-4-dependent non-canonical NLRP3 inflammasome pathways functioned during the interactions of Streptococcus mitis (S. mitis) and P. gingivalis with human THP-1 cells.

Results: IL-1β and NLRP3, NLRP6, NLRP12, and absent in melanoma 2 (AIM2) inflammasomes are highly expressed in gingival tissues with severe chronic periodontitis. In human THP-1 cells, P. gingivalis activates the synthesis and secretion of IL-1β to higher levels than S. mitis. Importantly, NLRP3-, Caspase-1-, and Caspase-4-siRNA knockdown THP-1 cells treated with P. gingivalis exhibited a lower expression level of IL-1β as compared to the control cells. In addition, silencing of either CASP4 or CASP1 can lead to a concurrent or reciprocal decrease in the expression of the other. Of note, the IL-1β induction is not affected in the S. mitis-treated THP-1 cells with the silence of NLRP3, Caspase-1, and Caspase-4 genes.

Conclusion: NLRP3/Caspase-4 and NLRP3/Caspase-1 dependent IL-1β production may crucially contribute to the dysregulated immuno-inflammatory response in periodontal pathogenesis.

Core Microbiota in Central Lung Cancer With Streptococcal Enrichment as a Possible Diagnostic Marker

BACKGROUND

Dysbiosis in lung cancer has been underexplored. The aim of this study was to define the bacterial and fungal microbiota of the bronchi in central lung cancer and to compare it with that of the oral and intestinal compartments.

METHODS

Twenty-five patients with central lung cancer and sixteen controls without antimicrobial intake during the previous month were recruited. Bacterial and fungal distribution was determined by massive sequencing of bronchial biopsies and saliva and faecal samples. Complex computational analysis was performed to define the core lung microbiota.

RESULTS

Affected and contralateral bronchi of patients have almost identical microbiota dominated by Streptococcus, whereas Pseudomonas was the dominant genera in controls. Oral and pulmonary ecosystems were significantly more similar in patients, probably due to microaspirations. Streptococcal abundance in the bronchi differentiated patients from controls according to a ROC curve analysis (90.9% sensitivity, 83.3% specificity, AUC=0.897). The saliva of patients characteristically showed a greater abundance of Streptococcus, Rothia, Gemella and Lactobacillus. The mycobiome of controls (Candida) was significantly different from that of patients (Malassezia). Cancer patients' bronchial mycobiome was similar to their saliva, but different from their contralateral bronchi.

CONCLUSIONS

The central lung cancer microbiome shows high levels of Streptococcus, and differs significantly in its composition from that of control subjects. Changes are not restricted to tumour tissue, and seem to be the consequence of microaspirations from the oral cavity. These findings could be useful in the screening and even diagnosis of this disease.