Characterization of MdpS: an in-depth analysis of a MUC5B-degrading protease from Streptococcus oralis

Oral biofilms, comprising hundreds of bacteria and other microorganisms on oral mucosal and dental surfaces, play a central role in oral health and disease dynamics. Streptococcus oralis, a key constituent of these biofilms, contributes significantly to the formation of which, serving as an early colonizer and microcolony scaffold. The interaction between S. oralis and the orally predominant mucin, MUC5B, is pivotal in biofilm development, yet the mechanism underlying MUC5B degradation remains poorly understood. This study introduces MdpS (Mucin Degrading Protease from Streptococcus oralis), a protease that extensively hydrolyses MUC5B and offers an insight into its evolutionary conservation, physicochemical properties, and substrate- and amino acid specificity. MdpS exhibits high sequence conservation within the species and also explicitly among early biofilm colonizing streptococci. It is a calcium or magnesium dependent serine protease with strict physicochemical preferences, including narrow pH and temperature tolerance, and high sensitivity to increasing concentrations of sodium chloride and reducing agents. Furthermore, MdpS primarily hydrolyzes proteins with O-glycans, but also shows activity toward immunoglobulins IgA1/2 and IgM, suggesting potential immunomodulatory effects. Significantly, MdpS extensively degrades MUC5B in the N- and C-terminal domains, emphasizing its role in mucin degradation, with implications for carbon and nitrogen sequestration for S. oralis or oral biofilm cross-feeding. Moreover, depending on substrate glycosylation, the amino acids serine, threonine or cysteine triggers the enzymatic action. Understanding the interplay between S. oralis and MUC5B, facilitated by MdpS, has significant implications for the management of a healthy eubiotic oral microenvironment, offering potential targets for interventions aimed at modulating oral biofilm composition and succession. Additionally, since MdpS does not rely on O-glycan removal prior to extensive peptide backbone hydrolysis, the MdpS data challenges the current model of MUC5B degradation. These findings emphasize the necessity for further research in this field.

Synergistic metabolism of salivary MUC5B in oral commensal bacteria during early biofilm formation

IMPORTANCE

The study of bacterial interactions and salivary-mediated regulation of early dental biofilm activity is of interest for understanding oral microbial adaptation to environmental cues and biofilm maturation. Findings in oral commensals can prove useful from the perspectives of both oral and systemic health of the host, as well as the understanding of general microbial biofilm physiology. The knowledge may provide a basis for the development of prognostic biomarkers, or development of new treatment strategies, related to oral health and disease and possibly also to other biofilm-induced conditions. The study is also an important step toward developing the methodology for similar studies in other species and/or growth conditions.

Mucin glycans drive oral microbial community composition and function

Human microbiome composition is closely tied to health, but how the host manages its microbial inhabitants remains unclear. One important, but understudied, factor is the natural host environment: mucus, which contains gel-forming glycoproteins (mucins) that display hundreds of glycan structures with potential regulatory function. Leveraging a tractable culture-based system to study how mucins influence oral microbial communities, we found that mucin glycans enable the coexistence of diverse microbes, while resisting disease-associated compositional shifts. Mucins from tissues with unique glycosylation differentially tuned microbial composition, as did isolated mucin glycan libraries, uncovering the importance of specific glycan patterns in microbiome modulation. We found that mucins shape microbial communities in several ways: serving as nutrients to support metabolic diversity, organizing spatial structure through reduced aggregation, and possibly limiting antagonism between competing taxa. Overall, this work identifies mucin glycans as a natural host mechanism and potential therapeutic intervention to maintain healthy microbial communities.

Characterization of a highly conserved MUC5B-degrading protease, MdpL, from Limosilactobacillus fermentum

MUC5B is the predominant glycoprotein in saliva and is instrumental in the establishment and maintenance of multi-species eubiotic biofilms in the oral cavity. Investigations of the aciduric Lactobacillaceae family, and its role in biofilms emphasizes the diversity across different genera of the proteolytic systems involved in the nutritional utilization of mucins. We have characterized a protease from Limosilactobacillus fermentum, MdpL (Mucin degrading protease from Limosilactobacillus) with a high protein backbone similarity with commensals that exploit mucins for attachment and nutrition. MdpL was shown to be associated with the bacterial cell surface, in close proximity to MUC5B, which was sequentially degraded into low molecular weight fragments. Mapping the substrate preference revealed multiple hydrolytic sites of proteins with a high O-glycan occurrence, although hydrolysis was not dependent on the presence of O-glycans. However, since proteolysis of immunoglobulins was absent, and general protease activity was low, a preference for glycoproteins similar to MUC5B in terms of glycosylation and structure is suggested. MdpL preferentially hydrolyzed C-terminally located hydrophobic residues in peptides larger than 20 amino acids, which hinted at a limited sequence preference. To secure proper enzyme folding and optimal conditions for activity, L. fermentum incorporates a complex system that establishes a reducing environment. The importance of overall reducing conditions was confirmed by the activity boosting effect of the added reducing agents L-cysteine and DTT. High activity was retained in low to neutral pH 5.5-7.0, but the enzyme was completely inhibited in the presence of Zn²⁺. Here we have characterized a highly conserved mucin degrading protease from L. fermentum. MdpL, that together with the recently discovered O-glycanase and O-glycoprotease enzyme groups, increases our understanding of mucin degradation and complex biofilm dynamics.

Analysis of the oral microbiome during hormonal cycle and its alterations in menopausal women: the "AMICA" project

The maintenance of human health is dependent on a symbiotic relationship between humans and associated bacteria. The diversity and abundance of each habitat's signature microbes vary widely among body areas and among them the oral microbiome plays a key role. Significant changes in the oral cavity, predominantly at salivary and periodontal level, have been associated with changes in estrogen levels. However, whether the oral microbiome is affected by hormonal level alterations is understudied. Hence the main objective pursued by AMICA project was to characterize the oral microbiome (saliva) in healthy women through: profiling studies using "omics" technologies (NMR-based metabolomics, targeted lipidomics by LC-MS, metagenomics by NGS); SinglePlex ELISA assays; glycosidase activity analyses and bioinformatic analysis. For this purpose, thirty-nine medically healthy women aged 26-77 years (19 with menstrual cycle and 20 in menopause) were recruited. Participants completed questionnaires assessing detailed medical and medication history and demographic characteristics. Plasmatic and salivary levels of sexual hormones were assessed (FSH, estradiol, LH and progesteron) at day 3 and 14 for women with menstrual cycle and only once for women in menopause. Salivary microbiome composition was assessed through meta-taxonomic 16S sequencing and overall, the salivary microbiome of most women remained relatively stable throughout the menstrual cycle and in menopause. Targeted lipidomics and untargeted metabolomics profiling were assessed through the use of LC-MS and NMR spectroscopy technologies, respectively and significant changes in terms of metabolites were identified in saliva of post-menopausal women in comparison to cycle. Moreover, glycosyl hydrolase activities were screened and showed that the β-D-hexosaminidase activity was the most present among those analyzed. Although this study has not identified significant alterations in the composition of the oral microbiome, multiomics analysis have revealed a strong correlation between 2-AG and α-mannosidase. In conclusion, the use of a multidisciplinary approach to investigate the oral microbiome of healthy women provided some indication about microbiome-derived predictive biomarkers that could be used in the future for developing new strategies to help to re-establish the correct hormonal balance in post-menopausal women.

Streptococcus gordonii Poised for Glycan Feeding through a MUC5B-Discriminating, Lipoteichoic Acid-Mediated Outside-In Signaling Circuit

Many oral bacteria employ cell wall-anchored adhesins to bind to the salivary films coating the teeth and mucosal surfaces. Surface binding prevents clearance and facilitates catabolism of salivary film glycoproteins. We asked whether Streptococcus gordonii adhesin expression changes in response to surface salivary cues using a eukaryote-like, outside-in recognition and signaling circuit. To determine whether the cues were discriminated, S. gordonii was tested during cell adhesion and biofilm formation on a MUC5B-rich or lower-molecular-mass salivary fraction or an uncoated abiotic surface. Cells were recovered and analyzed for differences in gene expression and proteins in cell wall fractions. In salivary-free conditions, planktonic S. gordonii presented three prominent cell wall LPXTG-motif proteins, SGO_1487, SGO_0890, and MbpA (mucin-binding protein A; SGO_0707). During biofilm formation on MUC5B-coated surfaces, MbpA, a MUC5B-binding protein, and key genes in the tagatose and quorum-sensing pathways were strongly promoted. The response to MUC5B required the two-component system (TCS), streptococcal regulator of adhesins sensor and regulator (SraSR, SGO_1180/81), lipoteichoic acid (LTA), and the homologous paired adhesins, SspA and SspB (SspAB). LTA appears to link the outside signal (MUC5B) to intramembrane SraSR. Tagatose pathway gene expression may poise cells to metabolize MUC5B glycans and, with a quorum-sensing gene (luxS), may direct formation of a consortium to facilitate glycan cross-feeding by S. gordonii. We now show that a Gram-positive bacterium discriminates specific surface environmental cues using an outside-in signaling mechanism to apparently optimize colonization of saliva-coated surfaces. IMPORTANCE All organisms throughout the tree of life sense and respond to their surface environments. To discriminate among mucosal surface environmental cues, we report that Streptococcus gordonii recognizes a high-molecular-weight mucin glycoprotein, MUC5B, using the paired adhesins SspAB and lipoteichoic acid; the latter bridges the outside signal to an intramembrane two-component system to transcriptionally regulate a MUC5B-specific adhesin and genes that may facilitate glycan catabolism.

Mucins 5b and 7 and secretory IgA in the oral acquired pellicle of children with caries and caries-free children

OBJECTIVE

The objective of this study was to determine whether differences in the abundance of mucins 5b and 7 as well as secretory IgA exist in the oral acquired pellicle between children with active caries and caries-free children.

DESIGN

Pellicle formation was performed for 10 min in-situ on ceramic slabs in the oral cavity of children (5-7 years of age) with caries (n = 15) and without signs of caries (n = 13). Furthermore, unstimulated saliva was collected. Concentrations of Muc5b, Muc7 and sIgA were measured in desorbed pellicle eluates and in saliva.

RESULTS

Significantly larger concentrations of Muc5b, Muc7 and sIgA were detected in the pellicle obtained from children with caries compared to caries-free children. However, in the salivary samples concentrations of mucins Muc5b and Muc7 as well as sIgA did not differ significantly between the two groups.

CONCLUSIONS

All three pellicle components Muc5b, Muc7 as well as sIgA could be identified as potential biomarkers for early childhood caries with high sensitivity and specificity. This could contribute to a better understanding of the different caries susceptibility in children.

A Tissue Section-Based Near-Infrared Spectroscopical Analysis of Salivary Gland Tumors

Simple Summary

Salivary gland tumors (SGTs) are a group of rare tumors that vary in clinical and histological behavior. Histological classification is difficult and requires an experienced pathologist. Based on recent research in other medical fields, this study investigated the value of near-infrared (NIR) spectroscopy in the diagnosis of SGTs supplementary to the histological investigation. The acquired spectra were analyzed with chemometric techniques. Enzymatic treatment (neuraminidase) resulted in spectral peak differences between healthy controls and different SGT types. Some malignant SGTs had higher spectral changes, suggesting bigger alterations in glycosylation of salivary mucins. Future biochemical research based on the further enzymatic dissection of SGTs and infrared spectroscopy could help pathologists to better understand the nature of these types of tumors.

Abstract

SGTs vary in histological behavior. Mucins, a major component in salivary glands, consist of a glycosylated and sialylated protein core. Rapid evolutions in glycobiology have demonstrated the important role of glycoproteins in cancer development. NIR spectroscopy is a method for the biochemical analysis of substrates. NIR spectra can be analyzed using specific chemometrics. Our aim was to explore the diagnostic possibilities of NIR spectroscopy in SGTs. 238 Hematoxylin and Eosine stained (H&E) SGT tissue sections were examined using NIR spectroscopy. 45 deparaffinized tissue sections were treated with neuraminidase to identify wavelengths in the NIR spectrum related to sialylation. NIR spectra were analyzed with chemometrics. NIR spectra could distinguish malignant SGTs from controls and benign SGTs. Prediction models based on the entire spectral range resulted in a 73.1% accurate classification of malignant SGTs and controls, while, based on neuraminidase experimental spectral peak differences (1436 nm; 1713 nm; 1783 nm; 1924 nm; 2032 nm; 2064 nm; 2178 nm; 2216 nm), an improved overall correct classification rate of 91.9% was obtained between healthy subjects and malignant tumors. H&E tissue section-based NIR spectroscopy can identify malignant SGTs from controls, promising an alternative method in the diagnosis of SGTs.

Proteomic response in Streptococcus gordonii DL1 biofilm cells during attachment to salivary MUC5B

Background

Salivary mucin MUC5B seems to promote biodiversity in dental biofilms, and thereby oral health, for example, by inducing synergistic ‘mucolytic’ activities in a variety of microbial species that need to cooperate for the release of nutrients from the complex glycoprotein. Knowledge of how early colonizers interact with host salivary proteins is integral to better understand the maturation of putatively harmful oral biofilms and could provide key insights into biofilm physiology.

Methods

The early oral colonizer Streptococcus gordonii DL1 was grown planktonically and in biofilm flow cell systems with uncoated, MUC5B or low-density salivary protein (LDP) coated surfaces. Bacterial cell proteins were extracted and analyzed using a quantitative mass spectrometry-based workflow, and differentially expressed proteins were identified.

Results and conclusions

Overall, the proteomic profiles of S. gordonii DL1 were similar across conditions. Six novel biofilm cell proteins and three planktonic proteins absent in all biofilm cultures were identified. These differences may provide insights into mechanisms for adaptation to biofilm growth in this species. Salivary MUC5B also elicited specific responses in the biofilm cell proteome. These regulations may represent mechanisms by which this mucin could promote colonization of the commensal S. gordonii in oral biofilms.

The pathogenic oral-gut-liver axis: new understandings and clinical implications

INTRODUCTION

Oral health is closely related to extra-oral disease status, as may be represented by the manifestations of gastrointestinal and liver diseases.

AREAS COVERED

This review focuses on the roles that the oral-gut or the oral-gut-liver axis play in the pathogenesis of inflammatory bowel disease, colorectal cancer, metabolic fatty liver disease, and nonalcoholic steatohepatitis. The discussion will begin with clinical data, including data from preclinical animal models, to elucidate mechanisms. We will also discuss ways to target oral dysbiosis and oral inflammation to treat gastrointestinal and liver diseases.

EXPERT OPINION

Several studies have demonstrated that oral pathobionts can translocate to the gastrointestinal tract where they contribute to inflammation and tumorigenesis. Furthermore, oral bacteria that migrate to the gastrointestinal tract can disseminate to the liver and cause hepatic disease. Thus, oral bacteria that ectopically colonize the intestine may serve as biomarkers for gastrointestinal and liver diseases. Also, understanding the characteristics of the oral-gut and oral-gut-liver microbial and immune axes will provide new insights into the pathogenesis of these diseases.

Acid tolerance in early colonizers of oral biofilms

Background

In caries, low pH drives selection and enrichment of acidogenic and aciduric bacteria in oral biofilms, and development of acid tolerance in early colonizers is thought to play a key role in this shift. Since previous studies have focussed on planktonic cells, the effect of biofilm growth as well as the role of a salivary pellicle on this process is largely unknown. We explored acid tolerance and acid tolerance response (ATR) induction in biofilm cells of both clinical and laboratory strains of three oral streptococcal species (Streptococcus gordonii, Streptococcus oralis and Streptococcus mutans) as well as two oral species of Actinomyces (A. naeslundii and A. odontolyticus) and examined the role of salivary proteins in acid tolerance development.

Methods

Biofilms were formed on surfaces in Ibidi® mini flow cells with or without a coating of salivary proteins and acid tolerance assessed by exposing them to a challenge known to kill non-acid tolerant cells (pH 3.5 for 30 min) followed by staining with LIVE/DEAD BacLight and confocal scanning laser microscopy. The ability to induce an ATR was assessed by exposing the biofilms to an adaptation pH (pH 5.5) for 2 hours prior to the low pH challenge.

Results

Biofilm formation significantly increased acid tolerance in all the clinical streptococcal strains (P < 0.05) whereas the laboratory strains varied in their response. In biofilms, S. oralis was much more acid tolerant than S. gordonii or S. mutans. A. naeslundii showed a significant increase in acid tolerance in biofilms compared to planktonic cells (P < 0.001) which was not seen for A. odontolyticus. All strains except S. oralis induced an ATR after pre-exposure to pH 5.5 (P < 0.05). The presence of a salivary pellicle enhanced both acid tolerance development and ATR induction in S. gordonii biofilms (P < 0.05) but did not affect the other bacteria to the same extent.

Conclusions

These findings suggest that factors such as surface contact, the presence of a salivary pellicle and sensing of environmental pH can contribute to the development of high levels of acid tolerance amongst early colonizers in oral biofilms which may be important in the initiation of caries.

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.

Uncovering Roles of Streptococcus gordonii SrtA-Processed Proteins in the Biofilm Lifestyle

Streptococcus gordonii is a commensal oral organism. Harmless in the oral cavity, S. gordonii is an opportunistic pathogen. S. gordonii adheres to body surfaces using surface adhesive proteins (adhesins), which are critical to subsequent formation of biofilm communities. As in most Gram-positive bacteria, S. gordonii surface proteins containing the C-terminal LPXTG motif cleavage sequence are processed by sortase A (SrtA) to become covalently attached to the cell wall. To characterize the functional diversity and redundancy in the family of SrtA-processed proteins, an S. gordonii DL1 markerless deletion mutant library was constructed of each of the 26 putative SrtA-processed proteins. Each library member was evaluated for growth in rich medium, biofilm formation on plastic, saliva and salivary fractions, cell surface hydrophobicity (CSH), hemagglutination, and integration into an ex vivo plaque biofilm community. Library members were compared to the non-SrtA-processed adhesins AbpA and AbpB. While no major growth differences in rich medium were observed, many S. gordonii LPXTG/A proteins impacted biofilm formation on one or more of the substrates. Several mutants showed significant differences in hemagglutination, hydrophobicity, or fitness in the ex vivo plaque model. From the identification of redundant and unique functions in these in vitro and ex vivo systems, functional stratification among the LPXTG/A proteins is apparent.IMPORTANCE S. gordonii interactions with its environment depend on the complement of cell wall proteins. A subset of these cell wall proteins requires processing by the enzyme sortase A (SrtA). The identification of SrtA-processed proteins and their functional characterization will help the community to better understand how S. gordonii engages with its surroundings, including other microbes, integrates into the plaque community, adheres to the tooth surface, and hematogenously disseminates to cause blood-borne infections. This study identified 26 putative SrtA-processed proteins through creation of a markerless deletion mutant library. The library was subject to functional screens that were chosen to better understand key aspects of S. gordonii physiology and pathogenesis.

A comparison between the structures of reconstituted salivary pellicles and oral mucin (MUC5B) films

HYPOTHESIS

Salivary pellicles i.e., thin films formed upon selective adsorption of saliva, protect oral surfaces against chemical and mechanical insults. Pellicles are also excellent aqueous lubricants. It is generally accepted that reconstituted pellicles have a two-layer structure, where the outer layer is mainly composed of MUC5B mucins. We hypothesized that by comparing the effect of ionic strength on reconstituted pellicles and MUC5B films we could gain further insight into the pellicle structure.

EXPERIMENTS

Salivary pellicles and MUC5B films reconstituted on solid surfaces were investigated at different ionic strengths by Force Spectroscopy, Quartz Crystal Microbalance with Dissipation, Null Ellipsometry and Neutron Reflectometry.

FINDINGS

Our results support the two-layer structure for reconstituted salivary pellicles. The outer layer swelled when ionic strength decreased, indicating a weak polyelectrolyte behavior. While initially the MUC5B films exhibited a similar tendency, this was followed by a drastic collapse indicating an interaction between exposed hydrophobic domains. This suggests that mucins in the pellicle outer layer form complexes with other salivary components that prevent this interaction. Lowering ionic strength below physiological values also led to a partial removal of the pellicle inner layer. Overall, our results highlight the importance that the interactions of mucins with other pellicle components play on their structure.

Mucins and Their Role in Shaping the Functions of Mucus Barriers

We review what is currently understood about how the structure of the primary solid component of mucus, the glycoprotein mucin, gives rise to the mechanical and biochemical properties of mucus that are required for it to perform its diverse physiological roles. Macroscale processes such as lubrication require mucus of a certain stiffness and spinnability, which are set by structural features of the mucin network, including the identity and density of cross-links and the degree of glycosylation. At the microscale, these same features affect the mechanical environment experienced by small particles and play a crucial role in establishing an interaction-based filter. Finally, mucin glycans are critical for regulating microbial interactions, serving as receptor binding sites for adhesion, as nutrient sources, and as environmental signals. We conclude by discussing how these structural principles can be used in the design of synthetic mucin-mimetic materials and provide suggestions for directions of future work in this field.

Evidence and Role for Bacterial Mucin Degradation in Cystic Fibrosis Airway Disease

Chronic lung infections in cystic fibrosis (CF) patients are composed of complex microbial communities that incite persistent inflammation and airway damage. Despite the high density of bacteria that colonize the lower airways, nutrient sources that sustain bacterial growth in vivo, and how those nutrients are derived, are not well characterized. In this study, we examined the possibility that mucins serve as an important carbon reservoir for the CF lung microbiota. While Pseudomonas aeruginosa was unable to efficiently utilize mucins in isolation, we found that anaerobic, mucin-fermenting bacteria could stimulate the robust growth of CF pathogens when provided intact mucins as a sole carbon source. 16S rRNA sequencing and enrichment culturing of sputum also identified that mucin-degrading anaerobes are ubiquitous in the airways of CF patients. The collective fermentative metabolism of these mucin-degrading communities in vitro generated amino acids and short chain fatty acids (propionate and acetate) during growth on mucin, and the same metabolites were also found in abundance within expectorated sputum. The significance of these findings was supported by in vivo P. aeruginosa gene expression, which revealed a heightened expression of genes required for the catabolism of propionate. Given that propionate is exclusively derived from bacterial fermentation, these data provide evidence for an important role of mucin fermenting bacteria in the carbon flux of the lower airways. More specifically, microorganisms typically defined as commensals may contribute to airway disease by degrading mucins, in turn providing nutrients for pathogens otherwise unable to efficiently obtain carbon in the lung.

Persistent CF lung infections are composed of hundreds of microbial taxa whose interactions contribute to respiratory failure. Despite their importance, the complex interplay between the lung microbiota and host environment is poorly understood. For example, the nutrients that sustain bacterial growth in vivo, and how those nutrients are derived, are not well characterized. We reveal that a subset of CF microbiota is capable of fermenting mucins for carbon and energy which, in-turn, can support the carbon demands of other respiratory pathogens in co-culture. Moreover, we show that metabolites consistent with mucin fermentation are abundant within airway secretions, highlighting a potential key role for fermentative metabolisms in CF lung disease. A thorough understanding of pathogen ecology in the CF airway and the nutritional dynamics that sustain their growth will have important implications for the design of new therapeutic strategies and the management of disease progression.

Differential Utilization of Basic Proline-Rich Glycoproteins during Growth of Oral Bacteria in Saliva

Although saliva is widely recognized as a primary source of carbon and nitrogen for growth of the dental plaque biofilm community, little is known about how different oral bacteria utilize specific salivary components. To address this question, 32 strains representing 16 genera commonly isolated from early plaque biofilms were compared for growth over two transfers in stimulated (by chewing Parafilm) whole saliva that was stabilized by heat treatment and dialysis. The cell densities, measured by quantitative PCR (qPCR), ranged from ∼1 × 10(6) to 1 × 10(7)/ml for strains of Streptococcus gordonii, Streptococcus oralis, and Streptococcus mitis and one strain of Streptococcus sanguinis Strains of Streptococcus mutans, Gemella haemolysans, and Granulicatella adiacens reached ∼1 × 10(5) to 1 × 10(6)/ml. In contrast, little or no growth was noted for three other strains of S. sanguinis, as well as for strains of Streptococcus parasanguinis, Streptococcus salivarius, Streptococcus vestibularis, Streptococcus sobrinus, Actinomyces spp., Abiotrophia defectiva, and Rothia dentocariosa SDS-PAGE, lectin blotting, and two-dimensional gel electrophoresis of saliva from cultures of S. gordonii, S. oralis, and S. mitis revealed species-specific differences in the degradation of basic proline-rich glycoproteins (PRG). In contrast, saliva from cultures of other bacteria was indistinguishable from control saliva. Species-dependent differences in the utilization of individual host sugars were minor. Thus, differences in salivary glycan foraging between oral species may be important to cross-feeding and cooperation between organisms in dental plaque biofilm development.

IMPORTANCE

Bacteria in the mouth use saliva for nutrition. How each of the many types of bacteria uses saliva is not clear. We show that a major protein in saliva, called PRG, is an important nutrition source for certain bacteria but not for others. PRG has many sugar molecules linked in chains, but the sugar is not available for bacteria until the chains are degraded. The bacteria that can grow by digesting this protein break the sugar chains into parts which not only support their own growth but could also be available to support the growth of those bacteria that cannot use the intact protein.

Antimicrobial peptides and their interaction with biofilms of medically relevant bacteria

Biofilm-associated infections represent one of the major threats of modern medicine. Biofilm-forming bacteria are encased in a complex mixture of extracellular polymeric substances (EPS) and acquire properties that render them highly tolerant to conventional antibiotics and host immune response. Therefore, there is a pressing demand of new drugs active against microbial biofilms. In this regard, antimicrobial peptides (AMPs) represent an option taken increasingly in consideration. After dissecting the peculiar biofilm features that may greatly affect the development of new antibiofilm drugs, the present article provides a general overview of the rationale behind the use of AMPs against biofilms of medically relevant bacteria and on the possible mechanisms of AMP-antibiofilm activity. An analysis of the interactions of AMPs with biofilm components, especially those constituting the EPS, and the obstacles and/or opportunities that may arise from such interactions in the development of new AMP-based antibiofilm strategies is also presented and discussed. This article is part of a Special Issue entitled: Antimicrobial Peptides edited by Karl Lohner and Kai Hilpert.

Growth of Candida albicans in human saliva is supported by low-molecular-mass compounds

Saliva plays a key role in the maintenance of a stable oral microflora. It contains antimicrobial compounds but also functions as a substrate for growth of bacteria under conditions of low external nutrient supply. Besides bacteria, yeasts, in particular Candida albicans, commonly inhabit the oral cavity. Under immunocompromised conditions, instantaneous outgrowth of this yeast occurs in oral carriers of C. albicans, suggesting that this yeast is able to survive in the oral cavity with saliva as sole source of growth substrate. The aim of the present study was to identify the salivary constituents that are used by C. albicans for growth and survival in saliva. In addition, we have explored the effect of growth in saliva on the susceptibility of C. albicans to histatin 5, a salivary antifungal peptide. It was found that C. albicans was able to grow in human saliva without addition of glucose, and in the stationary phase could survive for more than 400 h. Candida albicans grown in saliva was more than 10 times less susceptible for salivary histatin 5 than C. albicans cultured in Sabouraud medium.

Extracellular Glycoside Hydrolase Activities in the Human Oral Cavity

Carbohydrate availability shifts when bacteria attach to a surface and form biofilm. When salivary planktonic bacteria form an oral biofilm, a variety of polysaccharides and glycoproteins are the primary carbon sources; however, simple sugar availabilities are limited due to low diffusion from saliva to biofilm. We hypothesized that bacterial glycoside hydrolase (GH) activities would be higher in a biofilm than in saliva in order to maintain metabolism in a low-sugar, high-glycoprotein environment. Salivary bacteria from 13 healthy individuals were used to grow in vitro biofilm using two separate media, one with sucrose and the other limiting carbon sources to a complex carbohydrate. All six GHs measured were higher in vitro when grown in the medium with complex carbohydrate as the sole carbon source. We then collected saliva and overnight dental plaque samples from the same individuals and measured ex vivo activities for the same six enzymes to determine how oral microbial utilization of glycoconjugates shifts between the planktonic phase in saliva and the biofilm phase in overnight dental plaque. Overall higher GH activities were observed in plaque samples, in agreement with in vitro observation. A similar pattern was observed in GH activity profiles between in vitro and ex vivo data. 16S rRNA gene analysis showed that plaque samples had a higher abundance of microorganisms with larger number of GH gene sequences. These results suggest differences in sugar catabolism between the oral bacteria located in the biofilm and those in saliva.

Salivary mucin 19 glycoproteins: innate immune functions in Streptococcus mutans-induced caries in mice and evidence for expression in human saliva

Saliva functions in innate immunity of the oral cavity, protecting against demineralization of teeth (i.e. dental caries), a highly prevalent infectious disease associated with Streptococcus mutans, a pathogen also linked to endocarditis and atheromatous plaques. Gel-forming mucins are a major constituent of saliva. Because Muc19 is the dominant salivary gel-forming mucin in mice, we studied Muc19(-/-) mice for changes in innate immune functions of saliva in interactions with S. mutans. When challenged with S. mutans and a cariogenic diet, total smooth and sulcal surface lesions are more than 2- and 1.6-fold higher in Muc19(-/-) mice compared with wild type, whereas the severity of lesions are up to 6- and 10-fold higher, respectively. Furthermore, the oral microbiota of Muc19(-/-) mice display higher levels of indigenous streptococci. Results emphasize the importance of a single salivary constituent in the innate immune functions of saliva. In vitro studies of S. mutans and Muc19 interactions (i.e. adherence, aggregation, and biofilm formation) demonstrate Muc19 poorly aggregates S. mutans. Nonetheless, aggregation is enhanced upon adding Muc19 to saliva from Muc19(-/-) mice, indicating Muc19 assists in bacterial clearance through formation of heterotypic complexes with salivary constituents that bind S. mutans, thus representing a novel innate immune function for salivary gel-forming mucins. In humans, expression of salivary MUC19 is unclear. We find MUC19 transcripts in salivary glands of seven subjects and demonstrate MUC19 glycoproteins in glandular mucous cells and saliva. Similarities and differences between mice and humans in the expression and functions of salivary gel-forming mucins are discussed.

Polybacterial human disease: the ills of social networking

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Bacteria are typically found within complex microbial communities in nature.

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Molecular interactions between co-infecting bacteria can profoundly affect disease prognosis and treatment.

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In vivo models and genomic tools are providing new insights into interbacterial behavior during infection.

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There is potential to target interbacterial interactions as part of a therapeutic strategy.

Polybacterial diseases involve multiple organisms that act collectively to facilitate disease progression. Although this phenomenon was highlighted early in the 20th century, recent technological advances in diagnostics have led to the appreciation that many infections are far more complex than originally believed. Furthermore, it is apparent that although most treatments focus on the dominant bacterial species in an infection, other microbes, including commensals, can have a profound impact on both the response to therapy and virulence. Very little is known about the molecular mechanisms that underpin interactions between bacteria during such infections. Here, we discuss recent studies identifying and characterizing mechanisms of bacterial interaction and the biological processes they govern during certain diseases. We also highlight how possible strategies for targeting these interbacterial interactions may afford a route towards development of new therapies, with consequences for disease control.

Crystalline anatase-rich titanium can reduce adherence of oral streptococci

Dental implant abutments that emerge through the mucosa are rapidly covered with a salivary protein pellicle to which bacteria bind, initiating biofilm formation. In this study, adherence of early colonizing streptococci, Streptococcus gordonii, Streptococcus oralis, Streptococcus mitis and Streptococcus sanguinis to two saliva-coated anodically oxidized surfaces was compared with that on commercially pure titanium (CpTi). Near edge X-ray absorption (NEXAFS) showed crystalline anatase was more pronounced on the anodically oxidized surfaces than on the CpTi. As revealed by fluorescence microscopy, a four-species mixture, as well as individual bacterial species, exhibited lower adherence after 2 h to the saliva-coated, anatase-rich surfaces than to CpTi. Since wettability did not differ between the saliva-coated surfaces, differences in the concentration and/or configuration of salivary proteins on the anatase-rich surfaces may explain the reduced bacterial binding effect. Anatase-rich surfaces could thus contribute to reduced overall biofilm formation on dental implant abutments through diminished adherence of early colonizers.

Dynamic changes in saliva after acute mental stress

Stress-related variations of fluoride concentration in supernatant saliva and salivary sediment, salivary cortisol, total protein and pH after acute mental stress were assessed. The hypothesis was that stress reactions have no influence on these parameters. Thirty-four male students were distributed into two groups: first received the stress exposure followed by the same protocol two weeks later but without stress exposure, second underwent the protocol without stress exposure followed by the stress exposure two weeks later. The stressor was a public speech followed by tooth brushing. Saliva was collected before, immediately after stress induction and immediately, at 10, 30 and 120 min. after tooth brushing. Cortisol concentrations, total protein, intraoral pH, and fluoride content in saliva were measured. The data were analyzed statistically. Salivary sediment was ca 4.33% by weight of whole unstimulated saliva. Fluoride bioavailability was higher in salivary sediment than in supernatant saliva. The weight and fluoride concentration was not altered during 2 hours after stress exposure. After a public speech, the salivary cortisol concentration significantly increased after 20 minutes compared to the baseline. The salivary protein concentration and pH also increased. Public speaking influences protein concentration and salivary pH but does not alter the fluoride concentration of saliva.

Microbiota and their role in the pathogenesis of oral mucositis

Oral mucositis in patients undergoing cancer therapy is a significant problem. Its prevalence ranges between 20 and 100%, depending on treatment type and protocols and patient-based variables. Mucositis is self-limiting when uncomplicated by infection. Unfortunately, the incidence of developing a local or systemic infection during the course of the treatment is very high. At this stage, it is unclear which role oral microbiota play in the onset, duration, and severity of oral mucositis. Nevertheless, there is growing interest in this underexplored topic, and new studies are being undertaken to unravel their impact on the pathogenesis of mucositis.

Surface-associated MUC5B mucins promote protease activity in Lactobacillus fermentum biofilms

BACKGROUND

Mucosal surfaces are coated with layers of mucus gel that protect the underlying tissues and promote colonization by members of the commensal microflora. Lactobacillus fermentum is a common inhabitant of the oral cavity, gastrointestinal and reproductive tracts and is one of the most important lactic acid bacteria contributing to the formation of a healthy intestinal microflora. We have investigated the proteolytic activity in L. fermentum in response to interactions with the MUC5B mucin, which is a major component of mucus gels at sites colonized by this micro-organism.

METHODS

Biofilms of Lactobacillus fermentum were established in mini-flow cells in the presence or absence of human salivary MUC5B. The proteolytic activity of biofilm cells was examined in a confocal scanning laser microscope with a fluorescent protease substrate. Degradation of MUC5B by L. fermentum was analysed using SDS-PAGE followed by Western blotting with antisera raised against the MUC5B peptide. Cell surface proteins differentialy expressed in a MUC5B-rich environment were identified with the aid of comparative two-dimensional electrophoresis followed by LC-MS/MS.

RESULTS

Lactobacillus fermentum adhered well to surfaces coated with MUC5B mucin and in biofilms of L. fermentum formed in a MUC5B environment, the proportion of proteolytically-active cells (47 ± 0.6% of the population), as shown by cleavage of a fluorescent casein substrate, was significantly greater (p < 0.01) than that in biofilms formed in nutrient broth (0.4 ± 0.04% of the population). Thus, the presence of MUC5B mucins enhanced bacterial protease activity. This effect was mainly attributable to contact with surface-associated mucins rather than those present in the fluid phase. Biofilms of L. fermentum were capable of degrading MUC5B mucins suggesting that this complex glycoprotein can be exploited as a nutrient source by the bacteria.Comparison of the surface proteomes of biofilm cells of L. fermentum in a MUC5B environment with those in nutrient broth using two-dimensional electrophoresis and mass spectroscopy, showed that the enhanced proteolytic activity was associated with increased expression of a glycoprotease; O-sialoglycoprotein endopeptidase, as well as chaperone proteins such as DnaK and trigger factor.

CONCLUSIONS

Adhesion to mucin-coated surfaces leads to a shift towards a more protease-active phenotype within L. fermentum biofilms and proteases produced within the biofilms can degrade MUC5B mucins. The enhanced proteolytic activity was associated with an increase in O-sialoglycoprotein endopeptidase on the cell surface. We propose that the upregulation of chaperone proteins in the mucin environment may contribute to the protease-active phenotype through activation of the glycopeptidase. This would represent one way for commensal lactobacilli e.g. L. fermentum to exploit complex substrates in their local environment in order to survive on mucosal surfaces.

Salivary pellicles on titanium and their effect on metabolic activity in Streptococcus oralis

BACKGROUND

Titanium implants in the oral cavity are covered with a saliva-derived pellicle to which early colonizing microorganisms such as Streptococcus oralis can bind. The protein profiles of salivary pellicles on titanium have not been well characterized and the proteins of importance for binding are thus unknown. Biofilm bacteria exhibit different phenotypes from their planktonic counterparts and contact with salivary proteins may be one factor contributing to the induction of changes in physiology. We have characterized salivary pellicles from titanium surfaces and investigated how contact with uncoated and saliva-coated titanium surfaces affects metabolic activity in adherent cells of S. oralis.

METHODS

Salivary pellicles on smooth titanium surfaces were desorbed and these, as well as purified human saliva, were subjected to two-dimensional gel electrophoresis and mass spectroscopy. A parallel plate flow-cell model was used to study binding of a fresh isolate of S. oralis to uncoated and saliva-coated titanium surfaces. Metabolic activity was assessed using the BacLight CTC Vitality Kit and confocal scanning laser microscopy. Experiments were carried out in triplicate and the results analyzed using Student's t-test or ANOVA.

RESULTS

Secretory IgA, α-amylase and cystatins were identified as dominant proteins in the salivary pellicles. Selective adsorption of proteins was demonstrated by the enrichment of prolactin-inducible protein and absence of zinc-α₂-glycoprotein relative to saliva. Adherence of S. oralis to titanium led to an up-regulation of metabolic activity in the population after 2 hours. In the presence of a salivary pellicle, this effect was enhanced and sustained over the following 22 hour period.

CONCLUSIONS

We have shown that adherence to smooth titanium surfaces under flow causes an up-regulation of metabolic activity in the early oral colonizer S. oralis, most likely as part of an adaptation to the biofilm mode of life. The effect was enhanced by a salivary pellicle containing sIgA, α-amylase, cystatins and prolactin-inducible protein which was, for the first time, identified as an abundant component of salivary pellicles on titanium. Further studies are needed to clarify the mechanisms underlying the effect of surface contact on metabolic activity as well as to identify the salivary proteins responsible for enhancing the effect.

Structural Identification of O-Linked Oligosaccharides Using Exoglycosidases and MSn Together with UniCarb-DB Fragment Spectra Comparison

The availability of specific exoglycosidases alongside a spectral library of O-linked oligosaccharide collision induced dissociation (CID) MS fragments, UniCarb-DB, provides a pathway to make the elucidation of O-linked oligosaccharides more efficient. Here, we advise an approach of exoglycosidase-digestion of O-linked oligosaccharide mixtures, for structures that do not provide confirmative spectra. The combination of specific exoglycosidase digestion and MS2 matching of the exoglycosidase products with structures from UniCarb-DB, allowed the assignment of unknown structures. This approach was illustrated by treating sialylated core 2 O-linked oligosaccharides, released from the human synovial glycoprotein (lubricin), with a α2-3 specific sialidase. This methodology demonstrated the exclusive 3 linked nature of the sialylation of core 2 oligosaccharides on lubricin. When specific exoglycosidases were not available, MS3 spectral matching using standards was used. This allowed the unusual 4-linked terminal GlcNAc epitope in a porcine stomach to be identified in the GlcNAc1-4Galb1-3(GlcNAcb1-6)GalNAcol structure, indicating the antibacterial epitope GlcNAca1-4. In total, 13 structures were identified using exoglycosidase and MSn, alongside UniCarb-DB fragment spectra comparison. UniCarb-DB could also be used to identify the specificity of unknown exoglycosidases in human saliva. Endogenous salivary exoglycosidase activity on mucin oligosaccharides could be monitored by comparing the generated tandem MS spectra with those present in UniCarb-DB, showing that oral exoglycosidases were dominated by sialidases with a higher activity towards 3-linked sialic acid rather than 6-linked sialic acid.

Structural Identification of O-Linked Oligosaccharides Using Exoglycosidases and MSn Together with UniCarb-DB Fragment Spectra Comparison

The availability of specific exoglycosidases alongside a spectral library of O-linked oligosaccharide collision induced dissociation (CID) MS fragments, UniCarb-DB, provides a pathway to make the elucidation of O-linked oligosaccharides more efficient. Here, we advise an approach of exoglycosidase-digestion of O-linked oligosaccharide mixtures, for structures that do not provide confirmative spectra. The combination of specific exoglycosidase digestion and MS2 matching of the exoglycosidase products with structures from UniCarb-DB, allowed the assignment of unknown structures. This approach was illustrated by treating sialylated core 2 O-linked oligosaccharides, released from the human synovial glycoprotein (lubricin), with a α2-3 specific sialidase. This methodology demonstrated the exclusive 3 linked nature of the sialylation of core 2 oligosaccharides on lubricin. When specific exoglycosidases were not available, MS3 spectral matching using standards was used. This allowed the unusual 4-linked terminal GlcNAc epitope in a porcine stomach to be identified in the GlcNAc1-4Galb1-3(GlcNAcb1-6)GalNAcol structure, indicating the antibacterial epitope GlcNAca1-4. In total, 13 structures were identified using exoglycosidase and MSn, alongside UniCarb-DB fragment spectra comparison. UniCarb-DB could also be used to identify the specificity of unknown exoglycosidases in human saliva. Endogenous salivary exoglycosidase activity on mucin oligosaccharides could be monitored by comparing the generated tandem MS spectra with those present in UniCarb-DB, showing that oral exoglycosidases were dominated by sialidases with a higher activity towards 3-linked sialic acid rather than 6-linked sialic acid.

Rules of engagement: defining bacterial communication

Microbiologists often describe communication as occurring within and between bacterial species and even across the prokaryote-eukaryote divide. In a strictly evolutionary sense, however, communication should occur only rarely between unrelated organisms. Clearly, the microbiological and evolutionary definitions and standards for what qualifies as communication widely differ. In microbiology, the term "communication" is often used to denote any interaction between two organisms. Advancement in knowledge hinges on precise language and conceptual distinctions when introducing new scientific ideas. While terminology exists for describing interactions which are not true communication, excessive preoccupation with semantics may impede progress. Umbrella terms such as 'communication' are useful, but additional insight can be gained by understanding the fitness consequences and adaptive significance of behaviors observed in multispecies communities.

Oral multispecies biofilm development and the key role of cell-cell distance

Growth of oral bacteria in situ requires adhesion to a surface because the constant flow of host secretions thwarts the ability of planktonic cells to grow before they are swallowed. Therefore, oral bacteria evolved to form biofilms on hard tooth surfaces and on soft epithelial tissues, which often contain multiple bacterial species. Because these biofilms are easy to study, they have become the paradigm of multispecies biofilms. In this Review we describe the factors involved in the formation of these biofilms, including the initial adherence to the oral tissues and teeth, cooperation between bacterial species in the biofilm, signalling between the bacteria and its role in pathogenesis, and the transfer of DNA between bacteria. In all these aspects distance between cells of different species is integral for oral biofilm growth.

Effect of nanoporous TiO2 coating and anodized Ca2+ modification of titanium surfaces on early microbial biofilm formation

Background

The soft tissue around dental implants forms a barrier between the oral environment and the peri-implant bone and a crucial factor for long-term success of therapy is development of a good abutment/soft-tissue seal. Sol-gel derived nanoporous TiO₂ coatings have been shown to enhance soft-tissue attachment but their effect on adhesion and biofilm formation by oral bacteria is unknown.

Methods

We have investigated how the properties of surfaces that may be used on abutments: turned titanium, sol-gel nanoporous TiO₂ coated surfaces and anodized Ca²⁺ modified surfaces, affect biofilm formation by two early colonizers of the oral cavity: Streptococcus sanguinis and Actinomyces naeslundii. The bacteria were detected using 16S rRNA fluorescence in situ hybridization together with confocal laser scanning microscopy.

Results

Interferometry and atomic force microscopy revealed all the surfaces to be smooth (S_a ≤ 0.22 μm). Incubation with a consortium of S. sanguinis and A. naeslundii showed no differences in adhesion between the surfaces over 2 hours. After 14 hours, the level of biofilm growth was low and again, no differences between the surfaces were seen. The presence of saliva increased the biofilm biovolume of S. sanguinis and A. naeslundii ten-fold compared to when saliva was absent and this was due to increased adhesion rather than biofilm growth.

Conclusions

Nano-topographical modification of smooth titanium surfaces had no effect on adhesion or early biofilm formation by S. sanguinis and A. naeslundii as compared to turned surfaces or those treated with anodic oxidation in the presence of Ca²⁺. The presence of saliva led to a significantly greater biofilm biovolume but no significant differences were seen between the test surfaces. These data thus suggest that modification with sol-gel derived nanoporous TiO_2, which has been shown to improve osseointegration and soft-tissue healing in vivo, does not cause greater biofilm formation by the two oral commensal species tested than the other surfaces.

The road to ruin: the formation of disease-associated oral biofilms

The colonization of oral surfaces by micro-organisms occurs in a characteristic sequence of stages, each of which is potentially amenable to external intervention. The process begins with the adhesion of bacteria to host receptors on epithelial cells or in the salivary pellicle covering tooth surfaces. Interbacterial cell-cell binding interactions facilitate the attachment of new species and increase the diversity of the adherent microbial population. Microbial growth in oral biofilms is influenced by the exchange of chemical signals, metabolites and toxic products between neighbouring cells. Bacterial cells on tooth surfaces (dental plaque) produce extracellular polymers such as complex carbohydrates and nucleic acids. These large molecules form a protective matrix that contributes to the development of dental caries and, possibly, to periodontitis. The identification of key microbial factors underlying each step in the formation of oral biofilms will provide new opportunities for preventative or therapeutic measures aimed at controlling oral infectious diseases.

Talk of the town: interspecies communication in oral biofilms

Mature dental biofilms consist of towering microcolonies in which the resident bacterial cells interact with one another and exchange messages in the form of signalling molecules and metabolites. These structures have been compared with the bustling office blocks and apartment buildings of busy cities. Social and communication networks are the lifeblood of large communities, and there is mounting evidence that mutually beneficial interactions between microbial cells are essential to the development of biofilms in the oral cavity. This review discusses the mutualistic partnerships that form between oral bacteria, and the contribution of interspecies communication to the formation of mixed microbial communities.

Cultivation of a Synergistetes strain representing a previously uncultivated lineage

Subgingival plaque samples obtained from human subjects with periodontitis, shown to include previously uncultivable members of the phylum Synergistetes, were used to inoculate Cooked Meat Medium (CMM). The presence of Cluster A (uncultivable) Synergistetes was monitored by fluorescent in situ hybridization (FISH) and quantitative PCR (Q-PCR). Cluster A Synergistetes were found to grow in CMM in co-culture with other plaque bacteria and growth was stimulated by the addition of mucin and serum. Plaque samples were also used to inoculate Blood Agar (BA) plates and growth of Cluster A Synergistetes was revealed after anaerobic incubation, by colony hybridization with specific probes. Surface growth on the plates in regions identified by colony hybridization was harvested and used to inoculate fresh plates, thus enriching for Cluster A Synergistetes. Cross-streaks of other plaque bacteria were also used to stimulate Synergistetes growth. In the early passages, no discrete Synergistetes colonies were seen, but after eight passages and the use of cross-streaks of other bacteria present in the enriched community, colonies arose, which consisted solely of Cluster A Synergistetes cells, as determined by 16S rRNA gene PCR and cloning. This is the first report of the successful culture of a member of the uncultivable branch of this phylum.

Proteolytic degradation of human salivary MUC5B by dental biofilms

The degradation of complex substrates, like salivary mucins, requires an arsenal of glycosidases and proteases to sequentially degrade the oligosaccharides and polypeptide backbone. The mucin MUC5B is a complex oligomeric glycoprotein, heterogeneous in molecular mass (14-40 x 10(6) Da), with a diverse repertoire of oligosaccharides, differing in composition and charge. The aim of this study was to investigate whether proteolytic degradation of the mucin polypeptide backbone could be identified and if cooperation of dental biofilm bacteria was required. Cooperative bacteria-mediated proteolysis of MUC5B was determined by comparing individual species and mixed consortia of strains isolated from supragingival plaque, and freshly harvested supragingival plaque. Proteolytic activity was analysed using fluorescent labelled substrate and by visualizing mucin degradation by SDS-PAGE. Dental plaque degraded the polypeptide backbone of the salivary MUC5B mucin. The mucin was also degraded by a specific consortium of isolated species from supragingival plaque, although individual species and other consortia did not. Certain bacteria in supragingival dental plaque therefore cooperate as a consortium to proteolyse human salivary MUC5B and hydrolyse glycosides.

Image analysis software based on color segmentation for characterization of viability and physiological activity of biofilms

The novel image analysis software package bioImage_L was tested to calculate biofilm structural parameters in oral biofilms stained with dual-channel fluorescent markers. By identifying color tonalities in situ, the software independently processed the color subpopulations and characterized the viability and metabolic activity of biofilms.

Differential metabolic activity by dental plaque bacteria in association with two preparations of MUC5B mucins in solution and in biofilms

Salivary mucin, MUC5B, is an oligomeric glycoprotein, heterogeneous in size and with a diverse repertoire of oligosaccharides, which differ in composition and charge. Since complex salivary glycoproteins are considered to be the major source of nutrients for the oral supragingival microbiota, the major aim of the current study was to determine whether different preparations of non-denatured MUC5B could be isolated exhibiting different biological properties in relation to the microflora associated with the surfaces of the oral cavity. Two preparations, solMUC5B and gelMUC5B, were isolated by density-gradient centrifugation and were shown to have different buoyant densities, carbohydrate content and surface-adsorbing characteristics. To ascertain differences in biological activity, the two mucin preparations, both in solution and adsorbed to a model surface, were incubated with freshly isolated dental plaque and assayed for metabolic (dehydrogenase) activity with the fluoresecent substrate CTC (5-cyano-2,3-ditolyl tetrazolium chloride). The plaque bacteria exhibited higher metabolism with the solMUC5B preparation in solution, with 79.4 % active plaque cells compared to the controls without mucin (9.6 %), while gelMUC5B showed 48.2 % active cells with the same plaque population. In contrast, the same mucins adhered to a surface elicited a significantly lower metabolic response, with surface-associated plaque cells showing only 12.1 % active cells with solMUC5B and 29.2 % with gelMUC5B. These results suggested that the metabolism by the plaque cells adsorbed to surface-associated mucins was downregulated compared to the same cells suspended in mucin solution. This was confirmed in an experiment where active dispersed plaque/solMUC5B suspensions were shown to lose significant metabolic activity (e.g. 74.9 to 19.3 %) when allowed to interact with gelMUC5B adsorbed to a surface. Clearly, the solMUC5B and gelMUC5B preparations exhibited different biological activity when assayed with freshly plaque bacteria in suspension and in a biofilm.