Bacterial Biofilm in Salivary Gland Stones: Cause or Consequence?

Microbiomic association between the saliva and salivary stone in patients with sialolithiasis

Salivary stones, known as sialoliths, form within the salivary ducts due to abnormal salivary composition and cause painful symptoms, for which surgical removal is the primary treatment. This study explored the role of the salivary microbial communities in the formation of sialoliths. We conducted a comparative analysis of microbial communities present in the saliva and salivary stones, and sequenced the 16S rRNA gene in samples obtained from patients with sialoliths and from healthy individuals. Although the diversity in the saliva was high, the essential features of the microbial environment in sialoliths were low diversity and evenness. The association of microbial abundance between stones and saliva revealed a positive correlation between Peptostreptococcus and Porphyromonas, and a negative correlation for Pseudomonas in saliva. The functional potential differences between saliva and stones Bacterial chemotaxis and the citrate cycle were negatively correlated with most genera found in salivary stone samples. However, the functions required for organic compound degradation did not differ between the saliva samples. Although some microbes were shared between the sialoliths and saliva, their compositions differed significantly. Our study presents a novel comparison between salivary stones and salivary microbiomes, suggesting potential preventive strategies against sialolithiasis.

Identification of biological components for sialolith formation organized in circular multi-layers

According to the previous studies of sialolithiasis reported so far, this study is aimed to identify the biological components of sialolith, which show different ultrastructures and chemical compositions from other stones, cholelith and urolith. Twenty-two specimens obtained from 20 patients were examined histologically, and analyzed with micro-CT, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and transmission electron microscopy (TEM). All sialoliths (n = 22) observed in this study showed a central nidus, which was filled with organoid matrix admixed with exosome vesicles, loose calcium apatite crystals, and many bacteria. The micro-CT and SEM observation clearly defined a single or multiple central nidus(es) encircled by highly calcified compact zone. The circular compact zone showed a band-like calcification, about 1-3 mm in thickness, and usually located between the central nidus and the peripheral multilayer zone. But some sialoliths (n = 5) showed severe erosion of compact zone by expanding multilayered zone depending on the level of calcification and inflammation in sialolith. By observing TEM images, many exosome vesicles and degraded cytoplasmic organelles were found in the central nidus, and some epithelial cells were also found in the calcified matrix of peripheral multilayer zone. Particularly, EDS analysis indicated the highest Ca/P ratio in the intermediate compact zone (1.77), and followed by the central nidus area (1.39) and the peripheral multilayer zone (0.87). Taken together, these data suggest that the central nidus containing many inflammatory exosomes and degraded cytoplasmic organelles has a potential to induce a band-like calcification of compact zone, and followed by the additional multilayer deposition of exfoliated salivary epithelial cells as well as salivary materials. Thereby, the calcium apatite-based sialolith is gradually growing in its volume size, and eventually obstructs the salivary flow and provides a site for the bacterial infection.

Proteomic analysis of sialoliths from calcified, lipid and mixed groups as a source of potential biomarkers of deposit formation in the salivary glands

Salivary stones, also known as sialoliths, are formed in a pathological situation in the salivary glands. So far, neither the mechanism of their formation nor the factors predisposing to their formation are known despite several hypotheses. While they do not directly threaten human life, they significantly deteriorate the patient's quality of life. Although this is not a typical research material, attempts are made to apply various analytical tools to characterise sialoliths and search for the biomarkers in their proteomes. In this work, we used mass spectrometry and SWATH-MS qualitative and quantitative analysis to investigate the composition and select proteins that may contribute to solid deposits in the salivary glands. Twenty sialoliths, previously characterized spectroscopically and divided into the following groups: calcified (CAL), lipid (LIP) and mixed (MIX), were used for the study. Proteins unique for each of the groups were found, including: for the CAL group among them, e.g. proteins from the S100 group (S100 A8/A12 and P), mucin 7 (MUC7), keratins (KRT1/2/4/5/13), elastase (ELANE) or stomatin (STOM); proteins for the LIP group-transthyretin (TTR), lactotransferrin (LTF), matrix Gla protein (MPG), submandibular gland androgen-regulated protein 3 (SMR3A); mixed stones had the fewest unique proteins. Bacterial proteins present in sialoliths have also been identified. The analysis of the results indicates the possible role of bacterial infections, disturbances in calcium metabolism and neutrophil extracellular traps (NETs) in the formation of sialoliths.

Neutrophil Extracellular Trap-Driven Occlusive Diseases

The enlightenment of the formation of neutrophil extracellular traps (NETs) as a part of the innate immune system shed new insights into the pathologies of various diseases. The initial idea that NETs are a pivotal defense structure was gradually amended due to several deleterious effects in consecutive investigations. NETs formation is now considered a double-edged sword. The harmful effects are not limited to the induction of inflammation by NETs remnants but also include occlusions caused by aggregated NETs (aggNETs). The latter carries the risk of occluding tubular structures like vessels or ducts and appear to be associated with the pathologies of various diseases. In addition to life-threatening vascular clogging, other occlusions include painful stone formation in the biliary system, the kidneys, the prostate, and the appendix. AggNETs are also prone to occlude the ductal system of exocrine glands, as seen in ocular glands, salivary glands, and others. Last, but not least, they also clog the pancreatic ducts in a murine model of neutrophilia. In this regard, elucidating the mechanism of NETs-dependent occlusions is of crucial importance for the development of new therapeutic approaches. Therefore, the purpose of this review is to address the putative mechanisms of NETs-associated occlusions in the pathogenesis of disease, as well as prospective treatment modalities.

Magnesium whitlockite - omnipresent in pathological mineralisation of soft tissues but not a significant inorganic constituent of bone

Whitlockite is a calcium phosphate that was first identified in minerals collected from the Palermo Quarry, New Hampshire. The terms magnesium whitlockite [Mg-whitlockite; Ca₁₈Mg₂(HPO₄)₂(PO₄)₁₂] and beta-tricalcium phosphate [β-TCP; β-Ca₃(PO₄)₂] are often used interchangeably since Mg-whitlockite is not easily distinguished from β-Ca₃(PO₄)₂ by powder X-ray diffraction although their crystalline structures differ significantly. Being both osteoconductive and bioresorbable, Mg-whitlockite is pursued as a synthetic bone graft substitute. In recent years, advances in development of synthetic Mg-whitlockite have been accompanied by claims that Mg-whitlockite is the second most abundant inorganic constituent of bone, occupying as much as 20-35 wt% of the inorganic fraction. To find evidence in support of this notion, this review presents an exhaustive summary of Mg-whitlockite identification in biological tissues. Mg-whitlockite is mainly found in association with pathological mineralisation of various soft tissues and dental calculus, and occasionally with enamel and dentine. With the exception of high-temperature treated tumoural calcified deposits around interphalangeal and metacarpal joints and rhomboidal Mg-whitlockite crystals in post-apoptotic osteocyte lacunae in human alveolar bone, this unusual mineral has never been detected in the extracellular matrix of mammalian bone. Characterisation techniques capable of unequivocally distinguishing between different calcium phosphate phases, such as high-resolution imaging, crystallography, and/or spectroscopy have exclusively identified bone mineral as poorly crystalline, ion-substituted, carbonated apatite. The idea that Mg-whitlockite is a significant constituent of bone mineral remains unsubstantiated. Contrary to claims that such biomaterials represent a bioinspired/biomimetic approach to bone repair, Mg-whitlockite remains, exclusively, a pathological biomineral. STATEMENT OF SIGNIFICANCE: Magnesium whitlockite (Mg-whitlockite) is a unique calcium phosphate that typically features in pathological calcification of soft tissues; however, an alarming trend emerging in the synthetic bioceramics community claims that Mg-whitlockite occupies 20-35 wt% of bone mineral and therefore synthetic Mg-whitlockite represents a biomimetic approach towards bone regeneration. By providing an overview of Mg-whitlockite detection in biological tissues and scrutinising a diverse cross-section of literature relevant to bone composition analysis, this review concludes that Mg-whitlockite is exclusively a pathological biomineral, and having never been reported in bone extracellular matrix, Mg-whitlockite does not constitute a biomimetic strategy for bone repair.

Interpretation of the mucous plug through sialendoscopy

OBJECTIVE

The purpose of this manuscript is to highlight the behaviour of mucus inside the ducts of the major salivary glands, in presence of typical pathologies, through images obtained with sialendoscopy.

SUBJECT

The authors present and comment on some sialendoscopies that show mucous plug in the ducts of the major salivary glands.

RESULTS

In primary Sjogren's syndrome, mucous plugs confirm the qualitative anomaly of the mucins and acidification saliva. Instead, salivary calculations behave like foreign bodies that generate mechanical pressure and friction on the duct walls of major salivary glands, so mucus deposits in the duct in its defence; in case of infected stone, mucous plugs are formed also with the function of protecting the ducts from the aggression of germs. During sialadenitis, there is a conflict between mucus and bacteria which explains sialendoscopic evidence such as white duct walls and mucous plugs.

CONCLUSIONS

The study of the salivary ducts through sialendoscopy often confirms the clinical diagnosis or hypothesize it. During its execution, it is necessary not only to liberate the ducts of the major salivary glands but also analyse the appearance of the mucous plugs and the ductal walls as they are useful to guide the physician towards diagnosis.

Abscess Associated with Sialolith in a Parotid Duct - A Case Report

RATIONALE

The aim of this work is to describe the case of a large abscess associated with a sialolith in the parotid duct.

PATIENT CONCERNS

Patient's concern is evident in this pathology, because infection untreated or rapidly spreading infections can be potentially life-threatening secondary to airway compromise or septicemia.

DIAGNOSIS

Clinical examination, ultrasonography of the region, and cone beam computed tomography were requested to confirm the diagnosis of a sialolith associated with a large abscess.

TREATMENT

Antibiotic therapy with extraoral drainage was performed. After remission of the infection, the stone was located, removed, and the edges sutured.

OUTCOMES

The patient was followed for 6 months. There was a minimal scar without any other noteworthy change.

TAKE-AWAY LESSONS

The pathological changes involving the salivary glands are extremely important for diagnosis and treatment plan.

Bacterial Biofilm and its Role in the Pathogenesis of Disease

Recognition of the fact that bacterial biofilm may play a role in the pathogenesis of disease has led to an increased focus on identifying diseases that may be biofilm-related. Biofilm infections are typically chronic in nature, as biofilm-residing bacteria can be resilient to both the immune system, antibiotics, and other treatments. This is a comprehensive review describing biofilm diseases in the auditory, the cardiovascular, the digestive, the integumentary, the reproductive, the respiratory, and the urinary system. In most cases reviewed, the biofilms were identified through various imaging technics, in addition to other study approaches. The current knowledge on how biofilm may contribute to the pathogenesis of disease indicates a number of different mechanisms. This spans from biofilm being a mere reservoir of pathogenic bacteria, to playing a more active role, e.g., by contributing to inflammation. Observations also indicate that biofilm does not exclusively occur extracellularly, but may also be formed inside living cells. Furthermore, the presence of biofilm may contribute to development of cancer. In conclusion, this review shows that biofilm is part of many, probably most chronic infections. This is important knowledge for development of effective treatment strategies for such infections.

Bacterial biofilm in salivary stones

Purpose

To assess the susceptibility of salivary stones to bacterial biofilm formation, which may be involved in the development of salivary gland infection, and to investigate a relation between microbiological aspects and patient characteristics.

Methods

This prospective study comprises of 54 patients with sialolithiasis attended in Helsinki University Hospital during 2014–2016. A total of 55 salivary stones were removed, and studied for biofilm formation using fluorescence microscopy and sonication. The isolated organisms were quantified and identified using matrix-assisted laser desorption ionization time-of-flight mass spectrometry.

Results

Biofilm formation was confirmed on the surface of 39 (70.9%) stones. A total of 96 microorganisms were isolated from 45 salivary stones (81.8%). Two or more organisms were isolated in 33 (73.3%) cases. The main isolates were Streptococcus mitis/oralis (n = 27; 28.1%), followed by Streptococcus anginosus (n = 10; 9.6%), Rothia spp. (n = 8; 8.3%), Streptococcus constellatus (n = 7; 7.3%), and Streptococcus gordonii (n = 6; 6.2%). In all patients showing pre-operative (12 cases) or peri-operative (three cases) drainage of pus, the presence of biofilm was detected in microscopy (p = 0.004). Four patients showed post-operative infection, and in three of them (75.0%), the presence of biofilm was detected. Increased number of pus drainage was found among patients with reflux symptoms or use of proton-pump inhibitors.

Conclusions

Salivary stones are susceptible to bacterial biofilm formation, which could be related with the development and severity of the inflammation and the refractory nature of the disease. Sonication of salivary gland stones could be a useful method for finding the etiology of the chronic infection.

Evidence of a microbial etiology for sialoliths

OBJECTIVES

Sialolithiasis is the primary etiology for parotid and submandibular swelling, potentially resulting in discomfort, bacterial infections, and hospitalization. The etiology of sialolith formation is unknown. Currently, the proposed etiologies range from inflammation, coalescence of organic molecules, sialomicrolith formation, pH changes, and biofilm formation. In this study, we performed a descriptive analysis of images obtained through electron microscopy of sialoliths. Based on our findings and descriptive analysis, we hypothesize that sialolith formation is likely multifactorial and begins with biofilm formation. Biofilm formation then triggers a host immune response, and it is the interaction of biofilm with host immune cells and calcium nanoparticles that forms the nidus and creates a favorable environment for calcium precipitation.

METHODS

Sialoliths were extracted from patients and imaged under light and scanning electron microscopy. Specimens for light microscopy were prepared using a diamond saw. Specimens for electron microscopy were freeze-fractured, thus providing an undisturbed view of the core of the sialolith.

RESULTS

We were able to identify clear evidence of biofilm caves at the core of each sialolith. These biofilm caves were complex with the presence of bacteria and dehydrated extrapolysaccharide matrix, host cells (immune cells, platelets and erythrocytes), and calcium nanoparticles.

CONCLUSION

The etiology of sialolith formation is likely multifactorial. We propose that biofilm formation within a single salivary gland or duct leads to local ductal injury, which results in the influx of host immune cells that interact with the biofilm and calcium nanoparticles, creating a scaffold upon which further calcium deposition can occur.

LEVEL OF EVIDENCE

NA Laryngoscope, 130:69-74, 2020.

Removal of stones from the superficial lobe of the submandibular gland (SMG) via an intraoral endoscopy-assisted sialolithotomy

OBJECTIVES

Sialolithiasis is the most common cause of chronic sialadenitis of the submandibular gland (SMG). Symptomatic superficial lobe stones are often treated by submandibulectomy. A gland preserving operation allows for transoral stone removal through endoscopically assisted sialolithotomy. Herein, we provide clinical and sonographical follow-up data in patients who underwent sialolithotomy under general anesthesia.

MATERIALS AND METHODS

Sixty patients treated at the Department of Oral and Maxillofacial Surgery at Düsseldorf University Hospital for superficial lobe sialolithiasis of SMG were included in this study. All received transoral sialolithotomy under general anesthesia. Follow-up was conducted via standardized patient questionnaires, clinical examination, and B-mode and color Doppler sonography.

RESULTS

Mean patient age was 48.9 years. 56.6% of right and 43.4% of left SMG were affected. Mean follow-up was 45 months. Fifty-five of 59 detected stones could be removed. Mean operation time was 71 min. 3.3% of patients reported recurrent episodes of postoperative pain and 10% felt recurrent episodes of gland swelling. Persistent postoperative lingual nerve hypesthesia was described in one patient. No facial nerve damages occurred. Salivary flow rates remained reduced in most of the affected glands upon stone removal. Sonographical follow-up data of the previously affected SMG after intraoral endoscopy-assisted sialolithotomy showed a regular gland size in 70.8% of cases, a parenchyma free of inflammation in 93.8%, and without signs of fibrosis in 72.9% of cases. 68.7% of patients showed a regular structure of Wharton's duct at time of follow-up. In total, 89.6% of patients were diagnosed stone-free within both glands on follow-up. No case required subsequent submandibulectomy.

CONCLUSIONS

Sialolithotomy of Wharton's duct for removal of stones from the SMG's superficial lobe is a promising alternative to submandibulectomy.

CLINICAL RELEVANCE

Reduction of postoperative morbidity through endoscopically assisted sialolithotomy for removal of superficial lobe stones from SMG.

TRIAL REGISTRATION

Ethics Committee of Heinrich-Heine-University Düsseldorf (no. 5586).

Salivary calculi microbiota: new insights into microbial networks and pathogens reservoir

Sialolithiasis represents the most common disorders of salivary glands in middle-aged patients. It has been hypothesized that the retrograde migration of bacteria from the oral cavity to gland ducts may facilitate the formation of stones. Thus, in the present study, a microbiome characterization of salivary calculi was performed to evaluate the abundance and the potential correlations between microorganisms constituting the salivary calculi microbiota. Our data supported the presence of a core microbiota of sialoliths constituted principally by Streptococcus spp., Fusobacterium spp. and Eikenella spp., along with the presence of important pathogens commonly involved in infective sialoadenitis.

Morphological evidence of biofilm in chronic obstructive sialadenitis

OBJECTIVE

Bacterial infection is a common finding in acute sialadenitis and may play a role in the chronicity of the condition. This study investigated if bacterial biofilm is present in submandibular chronic obstructive sialadenitis.

METHODS

A descriptive case-control study was conducted that compared 10 histological sections of submandibular glands with chronic obstructive sialadenitis, to 10 histological sections of the healthy part of submandibular glands with pleomorphic adenoma. Fluorescence in situ hybridisation and confocal laser scanning microscopy visualised evidence of bacterial biofilm.

RESULTS

In the chronic obstructive sialadenitis group, 5 out of 10 histological sections showed morphological evidence of bacterial biofilm. In the control group, there was no sign of bacterial biofilm formation.

CONCLUSION

Morphological evidence of bacterial biofilm was found in the submandibular gland sections from patients with chronic sialadenitis and suggests a role in the chronicity of submandibular chronic obstructive sialadenitis.

Sialendoscopic management of autoimmune sialadenitis: a review of literature

Autoimmune diseases of major salivary glands include Sjögren's syndrome and a complex of disorders classified as immunoglobulin G4-related diseases. These pathologies are characterised by an autoimmune reaction mediated by T-helper lymphocytes that targets the ducts of exocrine glands in Sjögren's syndrome and glandular parenchyma in immunoglobulin G4-related diseases. Immunoglobulin G4-related diseases represent recently introduced multi-organ diseases that also involve the salivary glands. However, the morbid conditions once known as Mikulicz's disease and Kuttner's tumour were recently considered as two variants of immunoglobulin G4-related diseases affecting the major salivary glands ( immunoglobulin G4-related sialadenitis). This review briefly summarises the pathogenesis and clinical features of autoimmune diseases of the major salivary glands, focusing on the diagnostic and therapeutic role of sialendoscopy.

Is parotid saliva sterile on entry to the oral cavity?

CONCLUSION

The present study indicates that parotid saliva is sterile on entry to the oral cavity.

OBJECTIVES

The objective was to investigate if parotid saliva is sterile on entry to the oral cavity and, thus, prior to contamination by oral bacteria.

METHOD

Forty healthy volunteers were included in sterile parotid saliva collection. Parotid saliva was collected using a sterile Lashley cup, placed over the papilla of the Stensen´s duct, as well as sterile tubes and syringes for collection. All collections were followed by collection of a positive control sample where some of the sterile obtained parotid saliva had been exposed to the contralateral mucosal membranes. All samples parotid saliva, as well as the positive controls, were cultivated, and 10 randomly selected parotid saliva samples underwent polymerase chain reaction (PCR) analyses.

RESULTS

In 33 of 40 parotid saliva samples there were no cultivable bacteria, whereas bacteria were cultivated in all positive control samples. In eight of 10 PCR samples no bacterial DNA was detected. The most frequent bacteria in the remaining non-sterile parotid saliva samples and positive control samples were non-haemolytical streptococci and the coagulase negative staphylococci.