Next-generation sequencing of whole saliva from patients with primary Sjögren's syndrome and non-Sjögren's sicca reveals comparable salivary microbiota

Hyposalivation but not Sjögren's syndrome associated with microbial dysbiosis in women

Background

Saliva modulates the environment of the oral biofilm through pH buffer, microbial attachment to host surfaces, and nutritional source. The ecology of stress occurs when a physical factor adversely impacts an ecosystem or its biotic components. Therefore, reduced salivary flow can affect oral-host balance. The leading causes of hyposalivation include disease-associated Sjögren's syndrome (SS) and menopausal women as aging-associated. However, little is known about the oral microbiome integrated with sex hormones in hyposalivation. This study aimed to characterize the hyposalivation microbiome caused by aging or disease affecting the salivary glands in women.

Methods

We included 50 women older than 40 years of age in any menopausal phase. We collected stimulated saliva from 25 women diagnosed with SS (SS) and 25 without SS (non-SS). The bacterial profile of the patients was obtained by 16S rRNA sequencing. Bioinformatics analysis used machine learning to analyze the cohort's signs, symptoms, and bacterial profile. Salivary estradiol as a sex hormone variation level was determined.

Results

We obtained that 79% of the SS group, and 52% of the non-SS group had hyposalivation. We found a negatively correlated Prevotella-age and Rothia-estradiol in the SS group. Highlight, we found that the cause of the hyposalivation in the study did not explain differences in microbial diversity comparing non-SS and SS groups. Therefore, microbial communities found in hyposalivation but not related to systemic conditions suggest that changes in the oral environment might underpin host-microbial balance.

Conclusion

The salivary microbiome was similar in women with and without SS. However, hyposalivation showed two distinctive clusters associated with the bacterial population profiles. Our study suggests that local ecological disturbances could drive the change in the microbiome.

Oral microbial biomap in the drought environment: Sjogren's syndrome

Sjogren's syndrome (SS) is an autoimmune disease that affects primarily the salivary glands, making perturbations in the oral ecosystem and potential factors of salivary flow that influence the onset and development of the disease. The oral cavity contains diverse microorganisms that inhabit various niches such as the oral microbial "biomap." It does not seem specific enough to establish a characteristic microbiome, given the diversity of clinical manifestations, variable rates of salivary secretion, and influential risk factors in patients with SS. This review discusses the biogeography of the oral microbiome in patients with SS such as saliva, tongue, tooth, mucosa, and gum. The microorganisms that were more abundant in the different oral niches were Gram-positive species, suggesting a higher survival of cell wall bacteria in this arid oral environment. Reduced salivary flow appears not to be linked to the cause of dysbiosis alone but influences host-associated risk factors. However, much work remains to be done to establish the role of the microbiome in the etiopathogenesis of autoimmune diseases such as SS. Future studies of the microbiome in autoimmunity will shed light on the role of specific microorganisms that have never been linked before with SS.

The salivary microbiota is altered in cervical dysplasia patients and influenced by conization

This study supports the correlation between the salivary microbiota and cervical dysplasia and suggests that smoking influences the salivary microbiota.

Interactions between systemic diseases and oral microbiota shifts in the aging community: A narrative review

As a gateway to general health and a diverse microbial habitat, the oral cavity is colonized by numerous microorganisms such as bacteria, fungi, viruses, and archaea. Oral microbiota plays an essential role in preserving oral health. Besides, the oral cavity also significantly contributes to systemic health. Physiological aging influences all body systems, including the oral microbial inhabitants. The cited effect can cause diseases by forming dysbiotic communities. Since it has been demonstrated that microbial dysbiosis could disturb the symbiosis state between the host and the resident microorganism, shifting the condition toward a more pathogenic one, this study investigated how the oral microbial shifts in aging could associate with the development or progression of systemic diseases in older adults. The current study focused on the interactions between variations in the oral microbiome and prevalent diseases in older adults, including diabetes mellitus, Sjögren's syndrome, rheumatoid arthritis, pulmonary diseases, cardiovascular diseases, oral candidiasis, Parkinson's disease, Alzheimer's disease, and glaucoma. Underlying diseases can dynamically modify the oral ecology and the composition of its resident oral microbiome. Clinical, experimental, and epidemiological research suggests the associations of systemic disorders with bacteremia and inflammation after oral microbial changes in older adults.

High-Throughput Sequencing of Oral Microbiota in Candida Carriage Sjögren's Syndrome Patients: A Pilot Cross-Sectional Study

BACKGROUND

This study sought to characterize the saliva microbiota of Candida carriage Sjögren's syndrome (SS) patients compared to oral candidiasis and healthy patients by high-throughput sequencing.

METHODS

Fifteen patients were included, with five Candida carriage SS patients (decayed, missing, and filled teeth (DMFT) score 22), five oral candidiasis patients (DMFT score 17), and five caries active healthy patients (DMFT score 14). Bacterial 16S rRNA was extracted from rinsed whole saliva. PCR amplification generated DNA amplicons of the V3-V4 hypervariable region, which were sequenced on an Illumina HiSeq 2500 sequencing platform and compared and aligned to the SILVA database. Taxonomy abundance and community structure diversity was analyzed using Mothur software v1.40.0.

RESULTS

A total of 1016/1298/1085 operational taxonomic units (OTUs) were obtained from SS patients/oral candidiasis patient/healthy patients. Treponema, Lactobacillus, Streptococcus, Selenomonas, and Veillonella were the primary genera in the three groups. The most abundant significantly mutative taxonomy (OTU001) was Veillonella parvula. Microbial diversity (alpha diversity and beta diversity) was significantly increased in SS patients. ANOSIM analyses revealed significantly different microbial compositional heterogeneity in SS patients compared to oral candidiasis and healthy patients.

CONCLUSION

Microbial dysbiosis differs significantly in SS patients independent of oral Candida carriage and DMFT.

Microbial profiling of peri-implantitis compared to the periodontal microbiota in health and disease using 16S rRNA sequencing

PURPOSE

The objective of this study was to analyze the microbial profile of individuals with peri-implantitis (PI) compared to those of periodontally healthy (PH) subjects and periodontitis (PT) subjects using Illumina sequencing.

METHODS

Buccal, supragingival, and subgingival plaque samples were collected from 109 subjects (PH: 30, PT: 49, and PI: 30). The V3-V4 region of 16S rRNA was sequenced and analyzed to profile the plaque microbiota.

RESULTS

Microbial community diversity in the PI group was higher than in the other groups, and the 3 groups showed significantly separated clusters in the buccal samples. The PI group showed different patterns of relative abundance from those in the PH and PT groups depending on the sampling site at both genus and phylum levels. In all samples, some bacterial species presented considerably higher relative abundances in the PI group than in the PH and PT groups, including Anaerotignum lactatifermentans, Bacteroides vulgatus, Faecalibacterium prausnitzii, Olsenella uli, Parasutterella excrementihominis, Prevotella buccae, Pseudoramibacter alactolyticus, Treponema parvum, and Slackia exigua. Network analysis identified that several well-known periodontal pathogens and newly recognized bacteria were closely correlated with each other.

CONCLUSIONS

The composition of the microbiota was considerably different in PI subjects compared to PH and PT subjects, and these results could shed light on the mechanisms involved in the development of PI.

A Glimpse Into the Microbiome of Sjögren’s Syndrome

Sjögren’s syndrome (SS) is a common chronic systemic autoimmune disease and its main characteristic is lymphoid infiltration of the exocrine glands, particularly the salivary and lacrimal glands, leading to sicca symptoms of the mouth and eyes. Growing evidence has shown that SS is also characterized by microbial perturbations like other autoimmune diseases. Significant alterations in diversity, composition, and function of the microbiota were observed in SS. The dysbiosis of the microbiome correlates with worse symptoms and higher disease severity, suggesting that dysbiosis may be of great importance in the pathogenesis of SS. In this review, we provide a general view of recent studies describing the microbiota alterations of SS, the possible pathways that may cause microbiota dysbiosis to trigger SS, and the existence of the gut-ocular/gut-oral axis in SS.

The Oral Microbiome and Its Role in Systemic Autoimmune Diseases: A Systematic Review of Big Data Analysis

Introduction

Despite decades of research, systemic autoimmune diseases (SADs) continue to be a major global health concern and the etiology of these diseases is still not clear. To date, with the development of high-throughput techniques, increasing evidence indicated a key role of oral microbiome in the pathogenesis of SADs, and the alterations of oral microbiome may contribute to the disease emergence or evolution. This review is to present the latest knowledge on the relationship between the oral microbiome and SADs, focusing on the multiomics data generated from a large set of samples.

Methodology

By searching the PubMed and Embase databases, studies that investigated the oral microbiome of SADs, including systemic lupus erythematosus (SLE), rheumatoid arthritis (RA), and Sjögren's syndrome (SS), were systematically reviewed according to the PRISMA guidelines.

Results

One thousand and thirty-eight studies were found, and 25 studies were included: three referred to SLE, 12 referred to RA, nine referred to SS, and one to both SLE and SS. The 16S rRNA sequencing was the most frequent technique used. HOMD was the most common database aligned to and QIIME was the most popular pipeline for downstream analysis. Alterations in bacterial composition and population have been found in the oral samples of patients with SAD compared with the healthy controls. Results regarding candidate pathogens were not always in accordance, but Selenomonas and Veillonella were found significantly increased in three SADs, and Streptococcus was significantly decreased in the SADs compared with controls.

Conclusion

A large amount of sequencing data was collected from patients with SAD and controls in this systematic review. Oral microbial dysbiosis had been identified in these SADs, although the dysbiosis features were different among studies. There was a lack of standardized study methodology for each study from the inclusion criteria, sample type, sequencing platform, and referred database to downstream analysis pipeline and cutoff. Besides the genomics, transcriptomics, proteomics, and metabolomics technology should be used to investigate the oral microbiome of patients with SADs and also the at-risk individuals of disease development, which may provide us with a better understanding of the etiology of SADs and promote the development of the novel therapies.

Next generation sequencing-based salivary biomarkers in oral squamous cell carcinoma

Selection of potential disease-specific biomarkers from saliva or epithelial tissues through next generation sequencing (NGS)-based protein studies has recently become possible. The early diagnosis of oral squamous cell carcinoma (OSCC) has been difficult, if not impossible, until now due to the lack of an effective OSCC biomarker and efficient molecular validation method. The aim of this study was to summarize the advances in the application of NGS in cancer research and to propose potential proteomic and genomic saliva biomarkers for NGS-based study in OSCC screening and diagnosis programs. We have reviewed four categories including definitions and use of NGS, salivary biomarkers and OSCC, current biomarkers using the NGS-based technique, and potential salivary biomarker candidates in OSCC using NGS.

Why Should We Consider Potential Roles of Oral Bacteria in the Pathogenesis of Sjögren Syndrome?

Sjögren syndrome (SS) is a chronic autoimmune disorder that primarily targets the salivary and lacrimal glands. The pathology of these exocrine glands is characterized by periductal focal lymphocytic infiltrates, and both T cell-mediated tissue injury and autoantibodies that interfere with the secretion process underlie glandular hypofunction. In addition to these adaptive mechanisms, multiple innate immune pathways are dysregulated, particularly in the salivary gland epithelium. Our understanding of the pathogenetic mechanisms of SS has substantially improved during the past decade. In contrast to viral infection, bacterial infection has never been considered in the pathogenesis of SS. In this review, oral dysbiosis associated with SS and evidence for bacterial infection of the salivary glands in SS were reviewed. In addition, the potential contributions of bacterial infection to innate activation of ductal epithelial cells, plasmacytoid dendritic cells, and B cells and to the breach of tolerance via bystander activation of autoreactive T cells and molecular mimicry were discussed. The added roles of bacteria may extend our understanding of the pathogenetic mechanisms and therapeutic approaches for this autoimmune exocrinopathy.

Combined serum anti-SSA/Ro and salivary TRIM29 reveals promising high diagnostic accuracy in patients with primary Sjögren's syndrome

Objectives

To determine the diagnostic potential of simultaneous presence of serum anti-SSA/Ro and upregulated salivary protein biomarkers in patients with primary Sjögren’s syndrome (pSS).

Methods

Previous proteomics data on the intensity of neutrophil elastase, calreticulin, tripartite motif containing protein 29 (TRIM29), clusterin and vitronectin provided basis for performing extended analysis. Protein data was obtained by liquid chromatography tandem mass spectrometry technique in whole saliva from 24 patients with pSS and 16 patients having symptoms of pSS, but not fulfilling the American College of Rheumatology/European League against Rheumatism classification criteria (non-pSS). Serum anti-SSA/Ro antibody was measured using enzyme-linked immunosorbent assays. Receiver operating characteristic curve (ROC) value was calculated for combined biomarkers.

Results

Simultaneous presence of serum anti-SSA/Ro and upregulated salivary TRIM29 provided the most optimal combination with an area under curve (AUC) of 0.995 (95% CI 0.98–1.00, p = 2.0E-7 and standard error 0.007) and combinations of sensitivity and specificity within the interval of 91–100%. ROC analysis showed that salivary levels of TRIM29 alone enabled differentiation between pSS and non-pSS with an area under curve (AUC) of 0.88 (95%CI 0.77–1.00). All patients with pSS and 3 non-pSS patients were serum anti-SSA/Ro positive.

Conclusions

Simultaneous presence of serum anti-SSA/Ro and upregulated salivary TRIM29 provided a high diagnostic accuracy exceeding that of currently available tools used in pSS diagnostics. This biomarker combination represents a promising less invasive diagnostic tool for pSS. The clinical applicability of TRIM29 needs further testing in independent cohorts using relevant analytical techniques.

Old age and other factors associated with salivary microbiome variation

BACKGROUND

Many factors can contribute to the exact makeup of the salivary microbiome. Differences in the oral microbiome occur with old age, which may be due to oral conditions and diseases associated with old age, such as edentulism, as well as other unknown causes.

METHODS

The salivary microbiome was sampled in patients from a large urban clinic. For all subjects age, gender, periodontal status, caries status, presence of edentulism, medications, and tobacco usage were recorded. Multifactor analysis was used to study variation in salivary microbiome profiles linked to these factors.

RESULTS

In the population sampled, there were significantly higher numbers of edentulous subjects, and increased levels of polypharmacy found with aging. Large differences in alpha diversity and beta diversity of the salivary microbiome in the old age group were largely linked to edentulism. However, multivariable analysis revealed, even after adjusting for differences in edentulism, polypharmacy, tobacco usage, periodontal disease, caries level, and gender, that old age itself was associated with lower levels of taxa Porphyromonas endodontalis, Alloprevotella tannerae, Filifactor alocis, Treponema, Lautropia Mirabilis and Pseudopropionibacterium sp._HMT_194. Surprisingly, of these taxa, most were ones known to reside on or near tooth surfaces.

CONCLUSIONS

Another factor or factors beyond edentulism, polypharmacy and periodontal disease play a role in the differences seen in oral microbiome with old age. The nature of this factor(s) is not known.

Healthy Patients Are Not the Best Controls for Microbiome-Based Clinical Studies: Example of Sjögren's Syndrome in a Systematic Review

Introduction

It has been hypothesized that gut and oral dysbiosis may contribute to the development of primary Sjögren's syndrome (pSS). The aim of this systematic review was to assemble available data regarding the oral and gut microbiota in pSS and to compare them to data from healthy individuals and patients with dry symptoms without a diagnosis of Sjögren's syndrome or lupus disease to identify dysbiosis and discuss the results.

Methodology

Using the PRISMA guidelines, we systematically reviewed studies that compared the oral and gut microbiota of Sjögren's patients and controls. The PubMed database and Google Scholar were searched.

Results

Two-hundred and eighty-nine studies were found, and 18 studies were included: 13 referred to the oral microbiota, 4 referred to the gut microbiota, and 1 referred to both anatomical sites. The most frequent controls were healthy volunteers and patients with sicca symptoms. The most common analysis method used was 16S-targeted metagenomics. The results were mostly heterogeneous, and the results regarding diversity were not always in accordance. Dysbiosis in pSS was not confirmed, and reduced salivary secretion seems to explain more microbial changes than the underlying disease.

Conclusion

These heterogeneous results might be explained by the lack of a standardized methodology at each step of the process and highlight the need for guidelines. Our review provides evidence that sicca patients seem to be more relevant than healthy subjects as a control group.

Epithelial-immune cell interplay in primary Sjögren syndrome salivary gland pathogenesis

In primary Sjögren syndrome (pSS), the function of the salivary glands is often considerably reduced. Multiple innate immune pathways are likely dysregulated in the salivary gland epithelium in pSS, including the nuclear factor-κB pathway, the inflammasome and interferon signalling. The ductal cells of the salivary gland in pSS are characteristically surrounded by a CD4⁺ T cell-rich and B cell-rich infiltrate, implying a degree of communication between epithelial cells and immune cells. B cell infiltrates within the ducts can initiate the development of lymphoepithelial lesions, including basal ductal cell hyperplasia. Vice versa, the epithelium provides chronic activation signals to the glandular B cell fraction. This continuous stimulation might ultimately drive the development of mucosa-associated lymphoid tissue lymphoma. This Review discusses changes in the cells of the salivary gland epithelium in pSS (including acinar, ductal and progenitor cells), and the proposed interplay of these cells with environmental stimuli and the immune system. Current therapeutic options are insufficient to address both lymphocytic infiltration and salivary gland dysfunction. Successful rescue of salivary gland function in pSS will probably demand a multimodal therapeutic approach and an appreciation of the complicity of the salivary gland epithelium in the development of pSS.

Lozenges with probiotic strains enhance oral immune response and health

OBJECTIVE

Probiotics participate in regulating oral microbiota and reducing the prevalence of oral diseases; however, clinical research on probiotics is insufficient. Therefore, in this study, we performed in vitro screening of potential oral protective probiotic strains and then evaluated the clinical efficacy of the selected strains on maintaining oral health.

MATERIALS AND METHODS

Fifty healthy individuals were recruited and randomly assigned into the placebo group and probiotics group, which included three strains of probiotics, Lactobacillus salivarius subs. salicinius AP-32, Lactobacillus paracasei ET-66, and Lactobacillus plantarum LPL28. Each group was blindly administered placebo or probiotics for four weeks.

RESULTS

Next-generation sequencing results showed that the oral microbiota of Lactobacillus salivarius in the oral cavity were significantly increased in subjects supplemented with mixed probiotic lozenges. The anti-bacterial activities of viable probiotics were observed within two weeks. Both IgA levels and Lactobacillus and Bifidobacterium abundances in the oral cavity were significantly increased in the experimental groups, along with a reduced formation of plaque. Most participants reported that their oral health conditions and intestinal symptoms had improved.

CONCLUSIONS

Overall, our clinical study suggests that oral probiotic lozenges may enhance oral immunity, modulate oral microbiota, and improve oral health.

Distinct microRNA expression profiles in saliva and salivary gland tissue differentiate patients with primary Sjögren's syndrome from non-Sjögren's sicca patients

OBJECTIVES

Increasing evidence suggests that aberrant expression of microRNAs (miRNAs) is involved in the pathogenesis of primary Sjögren's syndrome (pSS). The aim was thus to characterize the miRNA profile in saliva, salivary gland tissue, and plasma from patients with pSS and compare findings with those of patients having Sjögren-like disease (non-pSS). In addition, to correlate miRNA levels and clinicopathological features of pSS.

METHODS

miRNA real-time quantitative polymerase chain reaction was performed on saliva, plasma, and salivary gland tissue samples from 24 patients with pSS and 16 non-pSS in 384-well plates. T test was used for comparison of miRNA profiles, followed by Benjamini-Hochberg correction. The discriminatory power of miRNAs was evaluated by receiver-operating characteristic curves, and Pearson/Spearman correlation was used for correlation analyses.

RESULTS

In saliva, 14 miRNAs were significantly differentially expressed between pSS and non-pSS, including downregulation of the miR-17 family in pSS. In salivary gland tissue of patients with pSS, miR-29a-3p was significantly upregulated. Plasma miRNAs did not differ between the two groups, although the miR-17 family tended to be downregulated. The combination of miR-17-5p and let-7i-5p in saliva yielded an area under curve of 97% (CI 92%-100%). Several miRNAs correlated significantly with one another and with salivary flow rates and histopathology.

CONCLUSION

Our findings indicate that the miRNA expression profile in saliva may enable to discriminate between pSS and non-pSS patients. However, further validation in larger cohorts is needed as well as functional analyses of the miRNAs of interest.

Characterizing Microbiota from Sjögren's Syndrome Patients

OBJECTIVE

To compare the oral microbiota of Sjögren's syndrome (SS) with that of healthy subjects (HS).

METHODS

Supragingival and subgingival biofilm samples were collected from the mesial-buccal tooth surfaces of SS patients (n = 57) and age- and sex-matched HS (n = 53). Unstimulated saliva and 8 oral tissue samples were taken using a buccal brush. Caries and periodontal measures were recorded. All supragingival samples and a subgroup of 24 SS and 28 HS subgingival samples, as well as 32 SS and 11 HS saliva and oral tissue samples, were analyzed for their content of 41 bacterial species using checkerboard DNA-DNA hybridization. Mean levels (×10⁵ ± SEM) and percentage of DNA probe counts of each species were determined for each sample site and averaged within subjects in the 2 clinical groups. Kruskal-Wallis tests, adjusting for multiple comparisons and cluster analysis, were used for soft tissue and microbial analysis, and the Mann-Whitney test was used to compare caries and periodontal measures.

RESULTS

Mean (×10⁵ ± SEM) total DNA probe counts in supragingival samples were significantly lower (P < 0.001) in the SS (13.3 ± .7) compared to the HS (44.1 ± 6.8) group. In supragingival samples, Veillonella parvula, Fusobacterium nucleatum ss vincenti, and Propionibacterium acnes were markedly elevated in the SS compared to the HS group in both mean (×10⁵ ± SEM) and mean (± SEM) percentage DNA probe counts (P < 0.001). In subgingival samples of SS, V. parvula was significantly different compared to HS (P < 0.05). SS was characterized by high levels of purple and low levels of orange and red complexes. Cluster analysis of oral tissues and saliva demonstrated that the mean microbial profiles for SS patients and the HS group clustered separately. Active root caries (P < 0.003) and attachment loss were significantly higher (P < 0.029) in the SS group compared to the HS group.

CONCLUSION

These findings indicate that saliva is a major controlling factor of intraoral biofilm. V. parvula may be a unique microbial biomarker for Sjögren's syndrome.

KNOWLEDGE TRANSFER STATEMENT

The microbiome characterized for Sjögren's syndrome in salivary hypofunction is shown to be under stress and reduced. Veillonella parvula can be a possible identification of a biomarker for Sjögren's syndrome.

Proteomics of saliva, plasma, and salivary gland tissue in Sjögren's syndrome and non-Sjögren patients identify novel biomarker candidates

OBJECTIVE

The aim of this study was to characterize and compare the proteome in whole saliva, plasma, and salivary gland tissue in patients with primary Sjögren's syndrome (pSS) and patients having symptoms of pSS, but not fulfilling the classification criteria, and to search for diagnostic biomarker candidates for pSS.

METHODS

Liquid chromatography tandem mass spectrometry was conducted on whole saliva, plasma, and labial salivary gland tissue samples from 24 patients with pSS and 16 non-Sjögren control subjects (non-pSS). Gene Ontology (GO)-terms and Kyoto Encyclopedia of Genes and Genomes (KEGG)-pathways were applied for functional annotation.

RESULTS

1013 proteins were identified in whole saliva, 219 in plasma, and 3166 in salivary gland tissue. In saliva, 40 proteins differed significantly between the two groups. In pSS, proteins involved in immunoinflammatory processes were upregulated, whereas proteins related to salivary secretion were downregulated. The combination of neutrophil elastase, calreticulin, and tripartite motif-containing protein 29 yielded a receiver-operating characteristic (ROC) value of 0.97 (CI 0.93-1.00). Protein expression in plasma and salivary gland tissue did not differ between the patient groups.

CONCLUSION

The salivary proteome of patients with pSS differed from that of non-pSS patients, indicating that saliva proteomics represents a promising non-invasive diagnostic tool for pSS.

SIGNIFICANCE

Primary Sjögren's syndrome (pSS) is a chronic systemic autoimmune disease, which clinically may present with a wide variety of symptoms and signs. Symptoms of dry eyes and dry mouth due to lacrimal and salivary gland dysfunction are prominent, but not pathognomonic, and an extensive diagnostic work-up including blood tests and labial salivary gland biopsy is often required to distinguish pSS from non-pSS. In this study, we used high throughput proteomics and identified a non-invasive biomarker candidate comprising a combination of three different upregulated salivary proteins, which enables differentiation between patients with pSS and non-pSS patients with an accuracy of 97%. In the future, this could contribute to earlier, more accurate and less costly diagnosis of pSS.

Oral Microbiota: Discovering and Facing the New Associations with Systemic Diseases

The economic crisis of the first decades of the 2000s had serious repercussions on the economy of individual countries, producing a gradual impoverishment of populations. The reduction in financial resources has significantly reduced citizens’ access to care, forcing them to abandon preventive medicine treatments and check-ups. The health of the oral cavity, which had long been considered of secondary importance when compared with systemic pathologies whose course can be potentially fatal for the patient, has therefore been strongly neglected. In recent years, however, new mechanisms of etiology of systemic diseases have been studied with the aim of evaluating some aspects still unknown. The microbiota, whose interest has grown considerably in the national scientific community, was immediately considered as a key factor in the pathogenesis of some disorders. These analyses have also benefited from numerous advances in the field of crop and molecular diagnostics in the microbiological field. Although pioneering studies have focused on the microbiota of the gastro-intestinal system, subsequent evidence has also been drawn from various studies conducted on the oral microbiota. What emerged is that oral microbiota dysbiosis has been associated with numerous systemic diseases. Therefore, the purpose of this Special Issue is to encourage scientific research on the topic of the relationship between the oral microbiota and systemic diseases, also inviting the use of new techniques for culture and molecular diagnosis. Particular attention will be given to original works in vivo and to literature reviews provided they are carried out with a systematic approach and, if possible, supported by additional quantitative analyses.

Dysbiotic oral microbiota and infected salivary glands in Sjögren's syndrome

Key events in the pathogenesis of Sjӧgren syndrome (SS) include the change of salivary gland epithelial cells into antigen-presenting cell-like phenotypes and focal lymphocytic sialadenitis (FLS). However, what triggers these features in SS is unknown. Dysbiosis of the gut and oral microbiomes is a potential environmental factor in SS, but its connection to the etiopathogenesis of SS remains unclear. This study aimed to characterize the oral microbiota in SS and to investigate its potential role in the pathogenesis of SS. Oral bacterial communities were collected by whole mouthwash from control subjects (14 without oral dryness and 11 with dryness) and primary SS patients (8 without oral dryness and 17 with dryness) and were analyzed by pyrosequencing. The SS oral microbiota was characterized by an increased bacterial load and Shannon diversity. Through comparisons of control and SS in combined samples and then separately in non-dry and dry conditions, SS-associated taxa independent of dryness were identified. Three SS-associated species and 2 control species were selected and used to challenge human submandibular gland tumor (HSG) cells. Among the selected SS-associated bacterial species, Prevotella melaninogenica uniquely upregulated the expression of MHC molecules, CD80, and IFNλ in HSG cells. Concomitantly, P. melaninogenica efficiently invaded HSG cells. Sections of labial salivary gland (LSG) biopsies from 8 non-SS subjects and 15 SS patients were subjected to in situ hybridization using universal and P. melaninogenica-specific probes. Ductal cells and the areas of infiltration were heavily infected with bacteria in the LSGs with FLS. Collectively, dysbiotic oral microbiota may initiate the deregulation of SGECs and the IFN signature through bacterial invasion into ductal cells. These findings may provide new insights into the etiopathogenesis of SS.