Inhibition of Streptococcus mutans biofilm formation by Streptococcus salivarius FruA

Competitive dynamics and balance between Streptococcus mutans and commensal streptococci in oral microecology

Dental caries, as a biofilm-related disease, is closely linked to dysbiosis in microbial ecology within dental biofilms. Beyond its impact on oral health, bacteria within the oral cavity pose systemic health risks by potentially entering the bloodstream, thereby increasing susceptibility to bacterial endocarditis, among other related diseases. Streptococcus mutans, a principal cariogenic bacterium, possesses virulence factors crucial to the pathogenesis of dental caries. Its ability to adhere to tooth surfaces, produce glucans for biofilm formation, and metabolize sugars into lactic acid contributes to enamel demineralization and the initiation of carious lesions. Its aciduricity and ability to produce bacteriocins enable a competitive advantage, allowing it to thrive in acidic environments and dominate in changing oral microenvironments. In contrast, commensal streptococci, such as Streptococcus sanguinis, Streptococcus gordonii, and Streptococcus salivarius, act as primary colonizers and compete with S. mutans for adherence sites and nutrients during biofilm formation. This competition involves the production of alkali, peroxides, and antibacterial substances, thereby inhibiting S. mutans growth and maintaining microbial balance. This dynamic interaction influences the balance of oral microbiota, with disruptions leading to shifts in microbial composition that are marked by rapid increases in S. mutans abundance, contributing to the onset of dental caries. Thus, understanding the dynamic interactions between commensal and pathogenic bacteria in oral microecology is important for developing effective strategies to promote oral health and prevent dental caries. This review highlights the roles and competitive interactions of commensal bacteria and S. mutans in oral microecology, emphasizing the importance of maintaining oral microbial balance for health, and discusses the pathological implications of perturbations in this balance.

Residents or Tourists: Is the Lactating Mammary Gland Colonized by Residential Microbiota?

The existence of the human milk microbiome has been widely recognized for almost two decades, with many studies examining its composition and relationship to maternal and infant health. However, the richness and viability of the human milk microbiota is surprisingly low. Given that the lactating mammary gland houses a warm and nutrient-rich environment and is in contact with the external environment, it may be expected that the lactating mammary gland would contain a high biomass microbiome. This discrepancy raises the question of whether the bacteria in milk come from true microbial colonization in the mammary gland ("residents") or are merely the result of constant influx from other bacterial sources ("tourists"). By drawing together data from animal, in vitro, and human studies, this review will examine the question of whether the lactating mammary gland is colonized by a residential microbiome.

Biofilm modifiers: The disparity in paradigm of oral biofilm ecosystem

A biofilm is a population of sessile microorganisms that has a distinct organized structure and characteristics like channels and projections. Good oral hygiene and reduction in the prevalence of periodontal diseases arise from minimal biofilm accumulation in the mouth, however, studies focusing on modifying the ecology of oral biofilms have not yet been consistently effective. The self-produced matrix of extracellular polymeric substances and greater antibiotic resistance make it difficult to target and eliminate biofilm infections, which lead to serious clinical consequences that are often lethal. Therefore, a better understanding is required to target and modify the ecology of biofilms in order to eradicate the infection, not only in instances of oral disorders but also in terms of nosocomial infections. The review focuses on several biofilm ecology modifiers to prevent biofilm infections, as well as the involvement of biofilm in antibiotic resistance, implants or in-dwelling device contamination, dental caries, and other periodontal disorders. It also discusses recent advances in nanotechnology that may lead to novel strategies for preventing and treating infections caused by biofilms as well as a novel outlook to infection control.

Staphylococcus aureus in Polymicrobial Skinand Soft Tissue Infections: Impact of Inter-Species Interactionsin Disease Outcome

Polymicrobial biofilms provide a complex environment where co-infecting microorganisms can behave antagonistically, additively, or synergistically to alter the disease outcome compared to monomicrobial infections. Staphylococcus aureus skin and soft tissue infections (Sa-SSTIs) are frequently reported in healthcare and community settings, and they can also involve other bacterial and fungal microorganisms. This polymicrobial aetiology is usually found in chronic wounds, such as diabetic foot ulcers, pressure ulcers, and burn wounds, where the establishment of multi-species biofilms in chronic wounds has been extensively described. This review article explores the recent updates on the microorganisms commonly found together with S. aureus in SSTIs, such as Pseudomonas aeruginosa, Escherichia coli, Enterococcus spp., Acinetobacter baumannii, and Candida albicans, among others. The molecular mechanisms behind these polymicrobial interactions in the context of infected wounds and their impact on pathogenesis and antimicrobial susceptibility are also revised.

Adjunctive role of Q10 with Ligilactobacillus salivarius, and Lactiplantibacillus plantarum probiotic Bacteria on the HEp-2 cells viability and adhesion of Streptococcus mutans

Objective

Various studies have indicated the application of Coenzyme Q10 and probiotic bacteria such as Ligilactobacillus salivarius (L. salivarius) and Lactiplantibacillus plantarum (L. plantarum) in combating periodontal disease. Considering the positive effect of these two on oral health, and the destructive effect of S. mutans, in this study, we investigate the outcomes of the administration of probiotics and Q10 on infected HEp-2 cell viability and S. mutans adhesion in different settings.

Methods

A 3-week-old human epidermoid laryngeal (HEp-2) cell line was cultured and exposed to two different probiotics and 3 different doses of Q10 doses. Samples were contaminated by S. mutans immediately (therapeutic setting) and after 3 hours (preventive setting). Eventually, the viability of HEp-2 cells was investigated by MTT. Also, the number of adhered S. mutans was explored by direct and indirect adhesion assays.

Results

L. plantarum and L. salivarius protect epithelial cells against S. mutans in both therapeutic and preventive settings, albeit not fully. In contrast, Q10 completely preserves the viability of infected Her HEp-2 cells at all concentrations. The effects of the coexistence of Q10 and probiotics were not quite equal, among which L. salivarius and 5 μg of Q10 form the best results. The microscopic adherence assay of S. mutans revealed that samples containing Q10 had significantly lower adhesion of probiotics and S. mutans to HEp-2 cells. Similarly, plates containing L. salivarius with 5μg or L. plantarum with 1μg Q10 or sole presence of L. salivarius had the lowest S. mutans adherence among others. Also, L. salivarius with 5μg Q10 had one of the highest probiotic adherences.

Conclusion

In conclusion, co-administration of Q10 and probiotics especially in presence of L. salivarius with 5μg Q10 could have remarkable effects on HEp-2 cell viability, S. mutans, and probiotic adherence. Nevertheless, our study, for the first time, showed that Q10 might have an anti-bacterial activity by suppressing the adhesion of tested bacteria to HEp-2 cells. This hypothesis, if correct, suggests that due to their different mechanisms, co-prescription of Q10 and probiotics may lead to better clinical responses, especially in the mentiond dose.

Drugs for the Quorum Sensing Inhibition of Oral Biofilm: New Frontiers and Insights in the Treatment of Periodontitis

Chemical molecules are used by microorganisms to communicate with each other. Quorum sensing is the mechanism through which microorganisms regulate their population density and activity with chemical signaling. The inhibition of quorum sensing, called quorum quenching, may disrupt oral biofilm formation, which is the main etiological factor of oral diseases, including periodontitis. Periodontitis is a chronic inflammatory disorder of infectious etiology involving the hard and soft periodontal tissues and which is related to various systemic disorders, including cardiovascular diseases, diabetes and obesity. The employment of adjuvant therapies to traditional scaling and root planing is currently being studied to further reduce the impact of periodontitis. In this sense, using antibiotics and antiseptics involves non-negligible risks, such as antibiotic resistance phenomena and hinders the re-establishment of eubiosis. Different quorum sensing signal molecules have been identified in periodontal pathogenic oral bacteria. In this regard, quorum sensing inhibitors are emerging as some interesting solutions for the management of periodontitis. Therefore, the aim of this review is to summarize the current state of knowledge on the mechanisms of quorum sensing signal molecules produced by oral biofilm and to analyze the potential of quorum sensing inhibitors for the management of periodontitis.

Quorum Sensing and Quorum Quenching with a Focus on Cariogenic and Periodontopathic Oral Biofilms

Numerous in vitro studies highlight the role of quorum sensing in the pathogenicity and virulence of biofilms. This narrative review discusses general principles in quorum sensing, including Gram-positive and Gram-negative models and the influence of flow, before focusing on quorum sensing and quorum quenching in cariogenic and periodontopathic biofilms. In cariology, quorum sensing centres on the role of Streptococcus mutans, and to a lesser extent Candida albicans, while Fusobacterium nucleatum and the red complex pathogens form the basis of the majority of the quorum sensing research on periodontopathic biofilms. Recent research highlights developments in quorum quenching, also known as quorum sensing inhibition, as a potential antimicrobial tool to attenuate the pathogenicity of oral biofilms by the inhibition of bacterial signalling networks. Quorum quenchers may be synthetic or derived from plant or bacterial products, or human saliva. Furthermore, biofilm inhibition by coating quorum sensing inhibitors on dental implant surfaces provides another potential application of quorum quenching technologies in dentistry. While the body of predominantly in vitro research presented here is steadily growing, the clinical value of quorum sensing inhibitors against in vivo oral polymicrobial biofilms needs to be ascertained.

The fruB Gene of Streptococcus mutans Encodes an Endo-Levanase That Enhances Growth on Levan and Influences Global Gene Expression

Streptococcus mutans, the primary etiologic agent of human dental caries, and a variety of oral Streptococcus and Actinomyces spp. synthesize high molecular mass homopolymers of fructose (fructans) with predominantly β2,1- (inulins) or β2,6-linkages (levans). The ability of S. mutans to degrade fructans contributes to the severity of dental caries. The extracellular product of fruA of S. mutans is an exo- β-d-fructofuranosidase that releases fructose from levan and inulin. Located 70 bp downstream of fruA, fruB encodes a member of the glycoside hydrolase family 32, but the function of FruB has not been established. Growth assays performed using wild-type UA159 and fruB-deficient derivatives, with fructans as the sole carbohydrate source, showed a significant reduction in the growth rate of a fruB mutant on levan, but not on inulin. A purified, recombinant FruB protein degraded levan to release mainly fructooligosaccharides. Driven by the fruA promoter and a secondary promoter located in the 3′ region of the fruA sequence, the fruB gene is inducible by fructose and especially by levan, but a stable stem-loop structure in the intergenic region likely modulates transcriptional read-through from fruA. Transcriptomic analysis of UA159 and a fruB mutant grown on 0.2% levan revealed differential expression of genes encoding ABC transporters, transcriptional regulators and genes involved in growth and stress tolerance. The ability of FruB to enhance levan metabolism and the high degree of conservation of FruB across S. mutans isolates imply a significant contribution of FruB to the fitness and virulence of this pathogen in human dental biofilms.

IMPORTANCE Carbohydrate metabolism and acid production are essential for the development of dental caries. As a by-product of sucrose metabolism, formation, and degradation of fructans enhances the severity of caries by S. mutans in animal models. This study highlights a significant breakthrough in identifying FruB in S. mutans as an endolevanase that contributes to efficient utilization of levan, a specific type of fructan produced by certain commensals but not S. mutans. Transcriptomic analysis revealed that FruB-dependent levan metabolism impacted global gene regulation, including a large number of novel genes. Considering the preference for levan by both FruA and FruB, the conservation of fruAB in S. mutans might represent a competitive advantage in access to the energy storage produced by dental microbiome. This is the first report demonstrating the presence of an endolevanase in S. mutans, therefore should be of broad interest to the fields of dental caries and complex carbohydrate metabolism.

Lipopolysaccharide associated with β-2,6 fructan mediates TLR4-dependent immunomodulatory activity in vitro

Levan, a β-2,6 fructofuranose polymer produced by microbial species, has been reported for its immunomodulatory properties via interaction with toll-like receptor 4 (TLR4) which recognises lipopolysaccharide (LPS). However, the molecular mechanisms underlying these interactions remain elusive. Here, we investigated the immunomodulatory properties of levan using thoroughly-purified and characterised samples from Erwinia herbicola and other sources. E. herbicola levan was purified by gel-permeation chromatography and LPS was removed from the levan following a novel alkali treatment developed in this study. E. herbicola levan was then characterised by gas chromatography-mass spectrometry and NMR. We found that levan containing LPS, but not LPS-depleted levan, induced TLR4-mediated cytokine production by bone marrow-derived dendritic cells and/or activated TLR4 reporter cells. These data indicated that the immunomodulatory properties of the levan toward TLR4-expressing immune cells were mediated by the LPS. This work also demonstrates the importance of LPS removal when assessing the immunomodulatory activity of polysaccharides.

Chlorhexidine versus organoselenium for inhibition of S. mutans biofilm, an in vitro study

Background

Chemical Plaque control by antimicrobial agent application can defend the teeth against caries. S. mutans is considered the main etiologic factor for caries. This was an in vitro study to compare between the efficacy of chlorhexidine diaceteate varnish, and an organoselenium sealant, to prevent S. mutans biofilm formation on human teeth.

Methods

Fourty five premolars extracted for orthodontic purposes were randomly divided into 3 groups of 15 teeth each. One control group and two test groups, chlorhexidine diaceteate varnish and an organoselenium sealant. The teeth were autoclaved before S. mutans biofilm was induced on to each in their respective groups. The reading T1 was taken for each tooth to assess the number of S. mutans attached in order to compare for differences in surface area among the 3 groups. The respective test materials were applied onto the teeth and biofilm induced onto them in their respective groups. The reading T2 was taken for the 2 test groups. The 3 groups were then subjected to aging for a period equivalent to 5 months before the biofilm was induced to take the reading T3 for the number of S. mutans. We used vortexing of the teeth to disrupt the biofilm at time points T1, T2 and T3. S. mutans count was then done using PCR.

Results

There were significantly lower S. mutans counts in the control group as compared to the chlorhexidine diacetate group at T3.There were no other statistically significant differences found.

Conclusion

Both organoselenium and Chlorhexidine diacetate do not inhibit S. mutans biofilm attachment onto the teeth.

β-Glycyrrhetinic acid inhibits the bacterial growth and biofilm formation by supragingival plaque commensals

β-Glycyrrhetinic acid (BGA) is a natural antibacterial agent. Previous studies reported that BGA has antibacterial effects against several bacteria. This study evaluated the effects of BGA on the regulation of supragingival plaque bacteria. First, the minimum inhibitory concentrations (MICs) of BGA against oral bacteria were measured. Next, the minimum concentrations for inhibition of biofilm formation were evaluated against Streptococcus mutans and Streptococcus sobrinus, possessing insoluble glucan synthesis abilities. The MICs of biofilm formation by these bacteria ranged from 1/8 to 2× MIC. Furthermore, the inhibition effects of BGA against the coaggregation of Porphyromonas gingivalis and Streptococcus gordonii were evaluated. BGA at 32 or 64 μg/mL inhibited the coaggregation of these bacteria after a 30 min incubation. Lastly, the inhibition effects of BGA against human supragingival plaque bacteria were evaluated. Human supragingival plaque samples were obtained from 12 healthy donors. The inhibition effects of BGA against biofilm formation by these plaque bacteria were evaluated. Of 12 samples, the biofilm formation by 11 was significantly attenuated by 128-256 μg/mL of BGA. The number of colony forming units in these biofilms was also significantly attenuated. In conclusion, it was revealed that BGA inhibits the growth and biofilm formation of bacteria, furthermore, the same effect was confirmed with supragingival plaque bacteria. BGA is a good candidate for a natural agent that prevents the outbreak and progression of periodontal disease because it suppresses not only the growth and biofilm formation of bacteria, but also the coaggregation of P. gingivalis with plaque bacteria.

Antimicrobial and Antibiofilm Activity of the Probiotic Strain Streptococcus salivarius K12 against Oral Potential Pathogens

Oral probiotics are increasingly used in the harmonization of the oral microbiota in the prevention or therapy of various oral diseases. Investigation of the antimicrobial activity of the bacteriocinogenic strain Streptococcus salivarius K12 against oral pathogens shows promising results, not only in suppressing growth, but also in eliminating biofilm formation. Based on these findings, we decided to investigate the antimicrobial and antibiofilm activity of the neutralized cell-free supernatant (nCFS) of S. salivarius K12 at various concentrations against selected potential oral pathogens under in vitro conditions on polystyrene microtiter plates. The nCFS of S. salivarius K12 significantly reduced growth (p < 0.01) in Streptococcus mutans Clarke with increasing concentration from 15 to 60 mg/mL and also in Staphylococcus hominis 41/6 at a concentration of 60 mg/mL (p < 0.001). Biofilm formation significantly decreased (p < 0.001) in Schaalia odontolytica P10 at nCFS concentrations of 60 and 30 mg/mL. Biofilm inhibition (p < 0.001) was also observed in Enterobacter cloacae 4/2 at a concentration of 60 mg/mL. In Schaalia odontolytica P10 and Enterobacter cloacae 4/2, the nCFS had no effect on their growth.

In vitro Streptococcus mutans adhesion and biofilm formation on different esthetic orthodontic archwires

OBJECTIVES

To evaluate the ability of different esthetic archwires to retain oral biofilms in vitro.

MATERIALS AND METHODS

Seven different brands of coated orthodontic archwires were tested: two epoxy coated, two polytetrafluoroethylene coated, two rhodium coated, and one silver plus polymer coated. Conventional uncoated metallic archwires were used as controls. Streptococus mutans adherence to archwires was quantified by colony count following 24 hours of biolfilm growth, and total wire-associated biofilm was measured using a crystal violet staining assay. For both tests, two conditions were used: 0% sucrose and 3% sucrose. For statistical analysis, P < .05 was considered as statistically significant.

RESULTS

For S. mutans colony forming units per biofilm, there were no statistically significant differences among the various archwires (P = .795 for 0% sucrose; P = .905 for 3% sucrose). Regarding total biofilm formed on archwires in the 3% sucrose condition, there were statistically significant differences in crystal violet staining only for the comparison between Niti Micro Dental White and Copper Ni-Ti wires (P < .05).

CONCLUSIONS

The clinical use of esthetic-coated orthodontic wires may be considered to have similar risks as uncoated archwires for biofilm retention.

Biofilm formation by Streptococcus mutans and its inhibition by green tea extracts

Dental Caries is considered one of the most existing and worldwide common diseases related to the oral cavity affecting both children and adults. Streptococcus mutans is the main cariogenic microorganism involved in the dental caries progression. Natural products such as herbal plants were found to have less side effects and economic value than those of the chemically synthesized antibiofilm agents. This study aimed to isolate Streptococcus mutans from different oral samples taken from saliva and dental plaques specimens to determine their capability for biofilm formation and to evaluate the antibiofilm activity of aqueous and alcoholic green tea extracts. The results revealed that 35, 4 and 1% of recovered dental plaque isolates exhibited strong, moderate and weak biofilm formation capabilities versus 26, 12 and 2% for those recovered from saliva. Two green tea extracts (aqueous and alcoholic) were tested for their antibiofilm formation activity against some selected S. mutans isolates. The results showed that the minimum biofilm inhibitory concentrations (MBICs) of the alcoholic and aqueous green tea extracts were in the range of 3.1 to 12.5 mg/ml and 6.5 to 50 mg/ml, respectively. Accordingly, green tea extracts can be incorporated in various oral preparations for preventing dental caries.

Protective Effects of the Probiotic Bacterium Streptococcus thermophilus on Candida albicans Morphogenesis and a Murine Model of Oral Candidiasis

Background

Oral candidiasis is a frequent form of candidiasis, caused by Candida species, in particular, Candida albicans (C. albicans). The transition of C. albicans from yeast to hyphae allows its attachment to epithelial cells, followed by biofilm formation, invasion, and tissue damage. Hence, we investigated the effect of Streptococcus salivarius subspecies thermophilus (S thermophilus) on the growth as well as biofilm and germ-tube formation of C. albicans both in vitro and in vivo in a murine model.

Methods

This experimental study was performed in the Department of Medical Mycology and Parasitology, School of Medicine, in collaboration with the Central Research Laboratory and the Comparative Biomedical Center, Shiraz University of Medical Sciences, Shiraz, Iran (2017 to 2018). The inhibitory activity of S. thermophilus against Candida species growth was evaluated using the broth microdilution method, and the inhibition of C. albicans biofilm formation was measured using the XTT assay. The inhibition of C. albicans germ-tube formation by S. thermophilus was evaluated using the plate assay and fluorescence microscopy. The experimental activity of the probiotic bacterium was assessed by culture and histopathological methods in six groups of five mice, comprising those treated with four concentrations of probiotics, fluconazole, and distilled water. The one-way analysis of variance, followed by a Tukey post hoc test, was used and a P value of less than 0.05 was considered significant.

Results

S. thermophilus inhibited Candida species growth at concentrations of 16 to 512 µg/mL. This probiotic inhibited the formation of C. albicans biofilms and germ tubes in a dose-dependent manner. S. thermophilus significantly reduced the colony-forming units in the mice receiving 30 mg/mL of this probiotic treatment compared with the control group (P=0.024). The histopathological analysis showed that Candida colonization was diminished in the mice following the administration of the probiotic.

Conclusion

Given the inhibitory activity of S. thermophilus against the growth, transition, and biofilm formation of C. albicans, it could be used in the management of oral candidiasis.

The Immunomodulatory Properties of β-2,6 Fructans: A Comprehensive Review

Polysaccharides such as β-2,1-linked fructans including inulin or fructose oligosaccharides are well-known prebiotics with recognised immunomodulatory properties. In recent years, other fructan types covering β-2,6-linked fructans, particularly microbial levans, have gained increasing interest in the field. β-2,6-linked fructans of different degrees of polymerisation can be synthesised by plants or microbes including those that reside in the gastrointestinal tract. Accumulating evidence suggests a role for these β-2,6 fructans in modulating immune function. Here, we provide an overview of the sources and structures of β-2,6 fructans from plants and microbes and describe their ability to modulate immune function in vitro and in vivo along with the suggested mechanisms underpinning their immunomodulatory properties. Further, we discuss the limitations and perspectives pertinent to current studies and the potential applications of β-2,6 fructans including in gut health.

In Vitro Anti-Biofilm and Antibacterial Properties of Streptococcus downii sp. nov

The aim of this study was to evaluate the potential anti-biofilm and antibacterial activities of Streptococcus downii sp. nov. To test anti-biofilm properties, Streptococcus mutans, Actinomyces naeslundii, Veillonella parvula, Fusobacterium nucleatum, Porphyromonas gingivalis, and Aggregatibacter actinomycetemcomitans were grown in a biofilm model in the presence or not of S. downii sp. nov. for up to 120 h. For the potential antibacterial activity, 24 h-biofilms were exposed to S. downii sp. nov for 24 and 48 h. Biofilms structures and bacterial viability were studied by microscopy, and the effect in bacterial load by quantitative polymerase chain reaction. A generalized linear model was constructed, and results were considered as statistically significant at p < 0.05. The presence of S. downii sp. nov. during biofilm development did not affect the structure of the community, but an anti-biofilm effect against S. mutans was observed (p < 0.001, after 96 and 120 h). For antibacterial activity, after 24 h of exposure to S. downii sp. nov., counts of S. mutans (p = 0.019) and A. actinomycetemcomitans (p = 0.020) were significantly reduced in well-structured biofilms. Although moderate, anti-biofilm and antibacterial activities of S. downii sp. nov. against oral bacteria, including some periodontal pathogens, were demonstrated in an in vitro biofilm model.

The potential of Streptococcus salivarius oral films in the management of dental caries: An inkjet printing approach

The use of probiotics, which can be administered in oro-dispersible films (ODFs) and have prolonged activity in the mouth, was explored. ODFs made of xylitol and containing Streptococcus salivarius were formulated using inkjet printing and tested against Streptococcus mutans - a causative organism of dental caries. The testing of the prepared ODFs involved co-incubating an ink-jetted formulation of S. salivarius and xylitol with S. mutans and monitoring the microbial growth kinetics in real-time using isothermal microcalorimetry and colony plate counts. Cell-free supernatants (CFS) of S. salivarius were also tested against S. mutans. The phosphate solubilisation potential of S. salivarius was also determined and found to be negative, an indication that the species will not deplete phosphate from teeth. From the tests, it was observed that the formulation reduced the S. mutans population from 7.9 to 5.04 Log CFU/mL post-calorimetry (approximately 3 Log reduction) which was comparable to the 99.9% reduction expected during antimicrobial activity testing. A gradual decrease in S. mutans population was also observed with increasing of CFS of S. salivarius volumes indicative of pathogen suppression. This study demonstrates that S. salivarius can be useful in managing dental caries and ODFs of S. salivarius can be formulated easily using ink-jetting for such management.

Suppressive Effects of Hainosan (Painongsan) against Biofilm Production by Streptococcus mutans

Streptococcus mutans, a bacterium that causes dental plaques, forms a biofilm on tooth surfaces. This biofilm can cause gingivitis by stimulating the gingival margin. However, there is no established treatment for biofilm removal. Hainosan (Painongsan), a traditional Japanese Kampo formula, has been used to treat gingivitis. Therefore, we investigated the biofilm suppressive effects of the hainosan extract (HNS) and its components on S. mutans. We conducted scanning electron microscopy and confocal laser microscopy analyses to clarify the anti-biofilm activities of HNS and its crude drugs. We also performed a quantitative RT-PCR assay to assess the biofilm-related gene expression. HNS showed a significant dose-dependent suppressive effect on biofilm formation. Both the scanning electron microscopy and confocal laser microscopy analyses also revealed the significant inhibitory effects of the extract on biofilm formation. Transmission electron microscopy analysis showed that HNS disrupted the surface of the bacterial wall. Furthermore, HNS reduced the hydrophobicity of the bacteria, and suppressed the mRNA expression of β-glucosyltransferase (gtfB), glucosyltransferase-SI (gtfC), and fructosyltransferase (ftf). Among the constituents of hainosan, the extract of the root of Platycodon grandiflorum (PG) showed the strongest biofilm suppression effect. Platycodin D, one of the constituent natural compounds of PG, inhibited S. mutans-associated biofilm. These findings indicate that hainosan eliminates dental plaques by suppressing biofilm formation by S. mutans.

Effects of Streptococcus salivarius K12 with nystatin on oral candidiasis-RCT

OBJECTIVE

To evaluate the efficacy and safety of Streptococcus salivarius K12 as an adjuvant in treating oral candidiasis.

METHODS

A total of 56 patients were participated in the randomized, double-blinded, placebo-controlled clinical trial. The S. salivarius K12 or placebo lozenges plus nystatin tablets were given for up to 4 weeks at 1-week interval and then followed up for 1 week thereafter. We collected and analyzed the mycological and clinical data, treatment course, and safety data.

RESULTS

At the end of the treatment, significant differences were found in the mycological cure rates between K12 group and control group (90.48% and 55.56%, respectively, p = 0.008). Survival analysis demonstrated no statistical difference in overall cure rates comprehensively considering mycological cure, clinical improvement, and recurrence (p = 0.078), while statistical difference was found in mycological cure (p = 0.013) between the two groups. The median treatment courses of K12 group and control group were 3 weeks and 4 weeks, respectively. No severe events were reported during the study.

CONCLUSION

Streptococcus salivarius K12 exhibited potential efficacy and safety as an adjuvant in treating oral candidiasis by enhancing mycological cure and shortening the treatment course of conventional antifungal therapy in this randomized, double-blinded, placebo-controlled clinical trial. Further large-scale clinical studies are desired to accumulate more evidence for its clinical applications.

Efficacy of a silver colloidal gel against selected oral bacteria in vitro

Background: It is necessary to develop new strategies to protect against bacteria such as S treptococcus mutans, S treptococcus sanguis, and Streptococcus salivarius, which contribute to tooth decay and plaque formation. Our current study investigated the efficacy of a colloidal silver gel in inhibiting biofilm formation by these principal oral bacteria , in vitro. The aim of this study was to assess the efficacy of a colloidal silver gel formulation for inhibiting bacterial biofilm formation (Ag-gel) by the principal bacteria that cause plaque formation and tooth decay.

Methods: The effect of Ag-gel on viability of S. mutans, S. sanguis, and S. salivarius was assessed by quantifying their colony forming units (CFU) in presence or absence of the test gel. The effect of this formulation on biofilm-forming ability of these bacteria was studied through scanning electron microscopy.

Results: Using the CFU assays, over 6 logs of inhibition (100%) were found for S. mutans, S. sanguis, and S. salivarius for the Ag-gel-treated bacteria when compared with the control gel. In addition, the Ag-gel also inhibited biofilm formation by these three bacteria mixed together. These results were confirmed by scanning electron microscopy.

Conclusions: The Ag-gel was effective in preventing biofilm formation by S. mutans, S. sanguis, and S. salivarius. This Ag-gel should be tested for the ability to block plaque formation in the mouth, through its use as a tooth paste.

Lactobacillus rhamnosus biosurfactant inhibits biofilm formation and gene expression of caries-inducing Streptococcus mutans

BACKGROUND

It is cleared that some probiotic strains inhibit biofilm formation of oral bacteria, but its mechanisms are not clearly understood yet. It is proposed that one of the mechanisms can be biosurfactant production, a structurally diverse group of surface-active compounds synthesized by microorganisms. Hence, this study focused on the evaluation of the anti-biofilm and antiadhesive activities of the L. rhamnosus derived-biosurfactant against Streptococcus mutans and its effect on gtfB/C and ftf genes expression level.

MATERIALS AND METHODS

In this in vitro study Lactobacillus rhamnosus ATCC7469 overnight culture was used for biosurfactant production. The biosurfactant effect on the surface tension reduction was confirmed by drop collapse method. Chemical bonds in the biosurfactant were identified by Fourier transform infrared (FTIR). Anti-biofilm and antiadhesive activities of the biosurfactant were determined on glass slides and in 96-well culture plates, respectively. The effect of the biosurfactant on gtfB/C and ftf genes expression level was also investigated after biofilm formation, total RNA extraction, and reverse transcription by quantitative real-time reverse transcriptase polymerase chain reaction (PCR) assay (quantitative PCR). The data were assessed by one-way analysis of variance in the Tukey-Kramer postdeviation test for all pairs. P < 0.05 was considered statistically significant.

RESULTS

The FTIR results of biosurfactant showed that it was protein rich. It also showed anti-biofilm formation activity on the glass slide and antiadhesive activity till 40% on microtiter plate wells. It also showed a significant reduction (P < 0.05) in gtfB/C and ftf genes expression level.

CONCLUSION

L. rhamnosus-derived biosurfactant exhibits a significant inhibitory effect on biofilm formation ability of S. mutans due to downregulation of biofilm formation associated genes, gtfB/C and ftf. L. rhamnosus-derived biosurfactant with substantial antiadhesive activity is suitable candidates for use in new generations of microbial antiadhesive agents.

Novel Assay To Characterize Neutrophil Responses to Oral Biofilms

Neutrophils, the most numerous leukocytes, play an important role in maintaining oral health through interactions with oral microbial biofilms. Both neutrophil hyperactivity and the bacterial subversion of neutrophil responses can cause inflammation-mediated tissue damage like that seen in periodontal disease. We describe here an assay that assesses neutrophil activation responses to monospecies biofilm bacteria in vitro based on the surface expression of cluster of differentiation (CD) markers associated with various neutrophil functions. Most of what we know about neutrophil responses to bacteria is based on in vitro assays that use planktonic bacteria and isolated/preactivated neutrophils, which makes interpretation of the neutrophil responses to bacteria a challenge. An understanding of how neutrophils differentially interact with and respond to commensal and pathogenic oral bacteria is necessary in order to further understand the neutrophil's role in maintaining oral health and the pathogenesis of periodontal disease. In this study, a flow cytometry-based in vitro assay was developed to characterize neutrophil activation states based on CD marker expressions in response to oral monospecies bacterial biofilms. Using this approach, changes in CD marker expressions in response to specific prominent oral commensal and pathogenic bacteria were assayed. Several functional assays, including assays for phagocytosis, production of reactive oxygen species, activation of the transcription factor Nrf2, neutrophil extracellular trap formation, and myeloperoxidase release, were also performed to correlate neutrophil function with CD marker expression. Our results demonstrate that neutrophils display bacterial species-specific responses. This assay can be used to characterize how specific biofilms alter specific neutrophil pathways associated with their activation.

Fighting biofilms with lantibiotics and other groups of bacteriocins

Biofilms are sessile communities of bacteria typically embedded in an extracellular polymeric matrix. Bacterial cells embedded in biofilms are inherently recalcitrant to antimicrobials, compared to cells existing in a planktonic state, and are notoriously difficult to eradicate once formed. Avenues to tackle biofilms thus far have largely focussed on attempting to disrupt the initial stages of biofilm formation, including adhesion and maturation of the biofilm. Such an approach is advantageous as the concentrations required to inhibit formation of biofilms are generally much lower than removing a fully established biofilm. The crisis of antibiotic resistance in clinical settings worldwide has been further exacerbated by the ability of certain pathogenic bacteria to form biofilms. Perhaps the most notorious biofilm formers described from a clinical viewpoint have been methicillin-resistant Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Pseudomonas aeruginosa, Gardnerella vaginalis and Streptococcus mutans, the latter of which is found in oral biofilms. Due to the dearth of novel antibiotics in recent decades, compounded by the increasing rate of emergence of resistance amongst pathogens with a propensity for biofilm formation, solutions are urgently required to mitigate these crises. Bacteriocins are a class of antimicrobial peptides, which are ribosomally synthesised and often are more potent than their antibiotic counterparts. Here, we review a selection of studies conducted with bacteriocins with the ultimate objective of inhibiting biofilms. Overall, a deeper understanding of the precise means by which a biofilm forms on a substrate as well as insights into the mechanisms by which bacteriocins inhibit biofilms is warranted.

Curcumin as a Promising Antibacterial Agent: Effects on Metabolism and Biofilm Formation in S. mutans

Streptococcus mutans (S. mutans) has been proved to be the main aetiological factor in dental caries. Curcumin, a natural product, has been shown to exhibit therapeutic antibacterial activity, suggesting that curcumin may be of clinical interest. The objective of this study is to evaluate the inhibitory effects of curcumin on metabolism and biofilm formation in S. mutans using a vitro biofilm model in an artificial oral environment. S. mutans biofilms were treated with varying concentrations of curcumin. The biofilm metabolism and biofilm biomass were assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and the crystal violet assay. Confocal laser scanning microscopy was used to analyse the composition and extracellular polysaccharide content of S. mutans biofilm after curcumin treatment. The biofilm structure was evaluated using a scanning electron microscope. The gene expression of virulence-related factors was assessed by real-time PCR. The antibiofilm effect of curcumin was compared with that of chlorhexidine. The sessile minimum inhibitory concentration (SMIC50%) of curcumin against S. mutans biofilm was 500 μM. Curcumin reduced the biofilm metabolism from 5 min to 24 h. Curcumin inhibited the quantity of live bacteria and total bacteria in both the short term (5 min) and the long term. Moreover, curcumin decreased the production of extracellular polysaccharide in the short term. The expression of genes related to extracellular polysaccharide synthesis, carbohydrate metabolism, adherence, and the two-component transduction system decreased after curcumin treatment. The chlorhexidine-treated group showed similar results. We speculate that curcumin has the capacity to be developed as an alternative agent with the potential to reduce the pathogenic traits of S. mutans biofilm.

Inhibiting effects of fructanase on competence-stimulating peptide-dependent quorum sensing system in Streptococcus mutans

Streptococcus mutans produces glucosyltransferases encoded by the gtfB and gtfC genes, which synthesize insoluble glucan, and both insoluble and soluble glucans by conversion of sucrose, and are known as principal agents to provide strong biofilm formation and demineralization on tooth surfaces. S. mutans possess a Com-dependent quorum sensing (QS) system, which is important for survival in severe conditions. The QS system is stimulated by the interaction between ComD {Receptor to competence-stimulating peptide (CSP)} encoded by the comD and CSP encoded by the comC, and importantly associated with bacteriocin production and genetic competence. Previously, we found enzyme fructanase (FruA) as a new inhibitor for the glucan-dependent biofilm formation. In the present study, inhibiting effects by FruA on glucan-independent biofilm formation of S. mutans UA159, UA159.gtfB^-, UA159.gtfC^-, and UA159.gtfBC^- were observed in sucrose and no sucrose sugars-supplemented conditions using the plate assay. The reduction of UA159.comC^- and UA159.comD^- biofilm formation were also observed as compared with UA159 in same conditions. These results suggested that inhibitions of glucan-independent and Com-dependent biofilm formation were involved in the inhibiting mechanism by FruA. To more thoroughly investigate effects by FruA on the QS system, we examined on CSP-stimulated and Com-dependent bacteriocin production and genetic transformation. FruA inhibited bacteriocin production in collaboration with CSP and genetic transformation in bacterial cell conditions treated with FruA. Our findings show that FruA has multiple effects that inhibit survival functions of S. mutans, including biofilm formation and CSP-dependent QS responses, indicating its potential use as an agent for prevention of dental caries.

Effect of antimicrobial photodynamic therapy on the counts of salivary Streptococcus mutans in children with severe early childhood caries

BACKGROUND

Antimicrobial photodynamic therapy (aPDT) is a novel technique for reduction of pathogenic microorganisms in dentistry. The aim of this study was to evaluate the effects of aPDT on Streptococcus mutans reduction in children with severe early childhood caries.

METHODS

Twenty-two children with severe early childhood caries aged 3-6 years were treated with toluoidine blue O (TBO) for 1min and irradiated by a Light Emitting Diode (LED; FotoSan, CMS Dental, Denmark) with the exposure time of 150s. Saliva samples were collected at baseline, 1h and 7 days after treatment. S. mutans counts were determined using the Dentocult SM Strip mutans.

RESULTS

The counts of S. mutans in saliva decreased significantly after 1h (P<0.001). However, the difference in reduction of S. mutans counts in saliva was not significant between the baseline and 7 days after treatment (P>0.05).

CONCLUSION

aPDT seems to be efficient to reduce salivary S. mutans immediately after treatment in children with severe early childhood caries. However, further research is needed to evaluate different doses and frequency of irradiation in combination with restoring carious teeth to find more durable results.

Oral cavities of healthy infants harbour high proportions of Streptococcus salivarius strains with phenotypic and genotypic resistance to multiple classes of antibiotics

Emerging antibiotic resistance in the oropharyngeal microbiota, of which Streptococcus salivarius is a prominent species, represents a challenge for treating paediatric populations. In this study, we investigated the role of Streptococcussalivarius as a reservoir for antibiotic resistance genes (ARG) in the oral microbiota by analysing 95 Streptococcussalivarius isolates from 22 healthy infants (2-16 months of age). MICs of penicillin G, amoxicillin, erythromycin, tetracycline, doxycycline and streptomycin were determined. ARG profiles were assessed in a subset of 21 strains by next-generation sequencing of genomes, followed by searches of assembled reads against the Comprehensive Antibiotic Resistance Database. Strains resistant to erythromycin, penicillins and tetracyclines were isolated from 83.3, 33.3 and 16.6 %, respectively, of infants aged 2 to 8 months with no prior antibiotic treatment. These percentages were100.0, 66.6 and 50.0 %, by 13 to 16 months of age. ARG or polymorphisms associated with antibiotic resistance were the most prevalent and involved genes for macrolide efflux (mel, mefA/E and macB), ribosomal protection [erm(B), tet(M) and tet(O)] and β-lactamase-like proteins. Phylogenetically related strains showing multidrug-resistant phenotypes harboured multidrug efflux ARG. Polymorphic genes associated with antibiotic resistance to drugs affecting DNA replication, folate synthesis, RNA/protein synthesis and regulators of antibiotic stress responses were detected. These data imply that Streptococcussalivarius strains established during maturation of the oral microbiota harbour a diverse array of functional ARG, even in the absence of antibiotic selective pressures, highlighting a potential role for this species in shaping antibiotic susceptibility profiles of oropharyngeal communities.

Capping Agent-Dependent Toxicity and Antimicrobial Activity of Silver Nanoparticles: An In Vitro Study. Concerns about Potential Application in Dental Practice

Objectives: In dentistry, silver nanoparticles (AgNPs) have drawn particular attention because of their wide antimicrobial activity spectrum. However, controversial information on AgNPs toxicity limited their use in oral infections. Therefore, the aim of the present study was to evaluate the antibacterial activities against a panel of oral pathogenic bacteria and bacterial biofilms together with potential cytotoxic effects on human gingival fibroblasts of 10 nm AgNPs: non-functionalized - uncapped (AgNPs-UC) as well as surface-functionalized with capping agent: lipoic acid (AgNPs-LA), polyethylene glycol (AgNPs-PEG) or tannic acid (AgNPs-TA) using silver nitrate (AgNO3) as control. Methods: The interaction of AgNPs with human gingival fibroblast cells (HGF-1) was evaluated using the mitochondrial metabolic potential assay (MTT). Antimicrobial activity of AgNPs was tested against anaerobic Gram-positive and Gram-negative bacteria isolated from patients with oral cavity and respiratory tract infections, and selected aerobic Staphylococci strains. Minimal inhibitory concentration (MIC) values were determined by the agar dilution method for anaerobic bacteria or broth microdilution method for reference Staphylococci strains and Streptococcus mutans. These strains were also used for antibiofilm activity of AgNPs. Results: The highest antimicrobial activities at nontoxic concentrations were observed for the uncapped AgNPs and the AgNPs capped with LA. It was found that AgNPs-LA and AgNPs-PEG demonstrated lower cytotoxicity as compared with the AgNPs-TA or AgNPs-UC in the gingival fibroblast model. All of the tested nanoparticles proved less toxic and demonstrated wider spectrum of antimicrobial activities than AgNO3 solution. Additionally, AgNPs-LA eradicated Staphylococcus epidermidis and Streptococcus mutans 1-day biofilm at concentration nontoxic to oral cells. Conclusions: Our results proved that a capping agent had significant influence on the antibacterial, antibiofilm activity and cytotoxicity of AgNPs. Clinical significance: This study highlighted potential usefulness of AgNPs against oral anaerobic Gram-positive and Gram-negative bacterial infections and aerobic Staphylococci strains provided that pharmacological activity and risk assessment are carefully performed.

Natural Immunoreactivity of Secretory IgA to Indigenous Strains of Streptococcus mutans From Chinese Spousal Pairs

Background

Dental caries is a well-known biofilm-mediated disease initiated by Streptococcus mutans, which should infect and colonize in a milieu perfused with components of the mucosal immune system. Little is known, however, regarding the relationship between the natural secretory IgA activity and S. mutans of a variety of diverse genotypes.

Objectives

The current study aimed to use spousal pairs to investigate the natural immunoreactivity of salivary secretory IgA to different genotype strains of S. mutans.

Patients and Methods

Indigenous strains were characterized from nine spousal pairs using polymerase reaction chain (PCR) and arbitrarily primed polymerase chain reaction (AP-PCR) by genotype monitoring. Unstimulated submandibular/sublingual secretions were collected and the concentrations of secretory IgA were determined by the enzyme-linked immunosorbent assay (ELISA). Each saliva sample was examined by Western blot to analyze the immunoreactivity of naturally occurring salivary secretory IgA antibodies for his/her own indigenous strain, spouse’s strain and reference strains including S. mutans GS-5 and Ingbritt (C).

Results

The results showed that naturally induced salivary IgA antibodies against S. mutans were present in all subjects. Almost all subjects had the similar individual immunoblotting profiles to different genotype strains.

Conclusions

The current study indicated that the immunoreactivity of secretory IgA might have no direct correlation with the colonization of indigenous flora and rejection of exogenous strains in adults. The relationship of microbes, host and dental caries should be in the light of coevolved microecosystem as a whole, but not caused by one factor alone.

Mechanisms of Competition in Biofilm Communities

Bacterial biofilms are dense and often mixed-species surface-attached communities in which bacteria coexist and compete for limited space and nutrients. Here we present the different antagonistic interactions described in biofilm environments and their underlying molecular mechanisms, along with ecological and evolutionary insights as to how competitive interactions arise and are maintained within biofilms.

Inhibition of Streptococcus mutans biofilm formation using extracts from Assam tea compared to green tea

OBJECTIVE

Streptococcus mutans, a gram-positive oral bacterium, has been identified as one of the principal etiological agents of human dental caries. To clarify the nature of the difference anti-biofilm effect against S. mutans between Assam tea from Camellia sinensis var. assamica, partially fermented, and green tea from Camellia sinensis, non-fermented, active agents from the teas were purified.

METHODS

Effects of Assam tea and green tea samples on biofilm were assessed by using the conventional titer plate method and the human saliva-coated hydroxyapatite discs. The purification and identification of inhibitors were performed by using ultrafiltration with centrifugal filter devices and high performance liquid chromatography.

RESULTS

Assam tea has stronger biofilm inhibition activity against S. mutans than green tea. A substance of <10kDa in mass in Assam tea had a high concentration of galloylated catechins and a stronger biofilm inhibiting activity than green tea. In contrast, substances >10kDa in mass from green tea included higher concentrations of polysaccharides composed of galacturonic acid, such as pectin, that enhance biofilm formation.

CONCLUSIONS

The higher concentrations of galloylated catechins in Assam tea may assist in prevention of dental caries, whereas in green tea, this mode of inhibition was likely offset by the presence of pectin. Purification of catechins in partially fermented Assam tea with lower-molecular-weight polysaccharide than pectin may be useful for developing oral care products such as toothpaste and oral care gel pastes.

Complete Genome Sequence of Streptococcus salivarius HSISS4, a Human Commensal Bacterium Highly Prevalent in the Digestive Tract

The human commensal bacterium Streptococcus salivarius plays a major role in the equilibrium of microbial communities of the digestive tract. Here, we report the first complete genome sequence of a Streptococcus salivarius strain isolated from the small intestine, namely, HSISS4. Its circular chromosome comprises 1,903 coding sequences and 2,100,988 nucleotides.

Actinomyces naeslundii GroEL-dependent initial attachment and biofilm formation in a flow cell system

Actinomyces naeslundii is an early colonizer with important roles in the development of the oral biofilm. The effects of butyric acid, one of short chain fatty acids in A. naeslundii biofilm formation was observed using a flow cell system with Tryptic soy broth without dextrose and with 0.25% sucrose (TSB sucrose). Significant biofilms were established involving live and dead cells in TSB sucrose with 60mM butyric acid but not in concentrations of 6, 30, 40, and 50mM. Biofilm formation failed in 60mM sodium butyrate but biofilm level in 60mM sodium butyrate (pH4.7) adjusted with hydrochloric acid as 60mM butyric media (pH4.7) was similar to biofilm levels in 60mM butyric acid. Therefore, butyric acid and low pH are required for significant biofilm formation in the flow cell. To determine the mechanism of biofilm formation, we investigated initial A. naeslundii colonization in various conditions and effects of anti-GroEL antibody. The initial colonization was observed in the 60mM butyric acid condition and anti-GroEL antibody inhibited the initial colonization. In conclusion, we established a new biofilm formation model in which butyric acid induces GroEL-dependent initial colonization of A. naeslundii resulting in significant biofilm formation in a flow system.

Genomics of Streptococcus salivarius, a major human commensal

The salivarius group of streptococci is of particular importance for humans. This group consists of three genetically similar species, Streptococcus salivarius, Streptococcus vestibularis and Streptococcus thermophilus. S. salivarius and S. vestibularis are commensal organisms that may occasionally cause opportunistic infections in humans, whereas S. thermophilus is a food bacterium widely used in dairy production. We developed Multilocus sequence typing (MLST) and comparative genomic analysis to confirm the clear separation of these three species. These analyses also identified a subgroup of four strains, with a core genome diverging by about 10%, in terms of its nucleotide sequence, from that of S. salivarius sensu stricto. S. thermophilus species displays a low level of nucleotide variability, due to its recent emergence with the development of agriculture. By contrast, nucleotide variability is high in the other two species of the salivarius group, reflecting their long-standing association with humans. The species of the salivarius group have genome sizes ranging from the smallest (∼ 1.7 Mb for S. thermophilus) to the largest (∼ 2.3 Mb for S. salivarius) among streptococci, reflecting genome reduction linked to a narrow, nutritionally rich environment for S. thermophilus, and natural, more competitive niches for the other two species. Analyses of genomic content have indicated that the core genes of S. salivarius account for about two thirds of the genome, indicating considerable variability of gene content and differences in potential adaptive features. Furthermore, we showed that the genome of this species is exceptionally rich in genes encoding surface factors, glycosyltransferases and response regulators. Evidence of widespread genetic exchanges was obtained, probably involving a natural competence system and the presence of diverse mobile elements. However, although the S. salivarius strains studied were isolated from several human body-related sites (all levels of the digestive tract, skin, breast milk, and body fluids) and included clinical strains, no genetic or genomic niche-specific features could be identified to discriminate specific group.

Intercellular communications in multispecies oral microbial communities

The oral cavity contains more than 700 microbial species that are engaged in extensive cell–cell interactions. These interactions contribute to the formation of highly structured multispecies communities, allow them to perform physiological functions, and induce synergistic pathogenesis. Co-adhesion between oral microbial species influences their colonization of oral cavity and effectuates, to a large extent, the temporal and spatial formation of highly organized polymicrobial community architecture. Individual species also compete and collaborate with other neighboring species through metabolic interactions, which not only modify the local microenvironment such as pH and the amount of oxygen, making it more suitable for the growth of other species, but also provide a metabolic framework for the participating microorganisms by maximizing their potential to extract energy from limited substrates. Direct physical contact of bacterial species with its neighboring co-habitants within microbial community could initiate signaling cascade and achieve modulation of gene expression in accordance with different species it is in contact with. In addition to communication through cell–cell contact, quorum sensing (QS) mediated by small signaling molecules such as competence-stimulating peptides (CSPs) and autoinducer-2 (AI-2), plays essential roles in bacterial physiology and ecology. This review will summarize the evidence that oral microbes participate in intercellular communications with co-inhabitants through cell contact-dependent physical interactions, metabolic interdependencies, as well as coordinative signaling systems to establish and maintain balanced microbial communities.

The virulence of Streptococcus mutans and the ability to form biofilms

In some diseases, a very important role is played by the ability of bacteria to form multi-dimensional complex structure known as biofilm. The most common disease of the oral cavity, known as dental caries, is a top leader. Streptococcus mutans, one of the many etiological factors of dental caries, is a microorganism which is able to acquire new properties allowing for the expression of pathogenicity determinants determining its virulence in specific environmental conditions. Through the mechanism of adhesion to a solid surface, S. mutans is capable of colonizing the oral cavity and also of forming bacterial biofilm. Additional properties enabling S. mutans to colonize the oral cavity include the ability to survive in an acidic environment and specific interaction with other microorganisms colonizing this ecosystem. This review is an attempt to establish which characteristics associated with biofilm formation--virulence determinants of S. mutans--are responsible for the development of dental caries. In order to extend the knowledge of the nature of Streptococcus infections, an attempt to face the following problems will be made: Biofilm formation as a complex process of protein-bacterium interaction. To what extent do microorganisms of the cariogenic flora exemplified by S. mutans differ in virulence determinants "expression" from microorganisms of physiological flora? How does the environment of the oral cavity and its microorganisms affect the biofilm formation of dominant species? How do selected inhibitors affect the biofilm formation of cariogenic microorganisms?

Community interactions of oral streptococci

It is now clear that the most common oral diseases, dental caries and periodontitis, are caused by mixed-species communities rather than by individual pathogens working in isolation. Oral streptococci are central to these disease processes since they are frequently the first microorganisms to colonize oral surfaces and they are numerically the dominant microorganisms in the human mouth. Numerous interactions between oral streptococci and other bacteria have been documented. These are thought to be critical for the development of mixed-species oral microbial communities and for the transition from oral health to disease. Recent metagenomic studies are beginning to shed light on the co-occurrence patterns of streptococci with other oral bacteria. Refinements in microscopy techniques and biofilm models are providing detailed insights into the spatial distribution of streptococci in oral biofilms. Targeted genetic manipulation is increasingly being applied for the analysis of specific genes and networks that modulate interspecies interactions. From this work, it is clear that streptococci produce a range of extracellular factors that promote their integration into mixed-species communities and enable them to form social networks with neighboring taxa. These "community integration factors" include coaggregation-mediating adhesins and receptors, small signaling molecules such as peptides or autoinducer-2, bacteriocins, by-products of metabolism including hydrogen peroxide and lactic acid, and a range of extracellular enzymes. Here, we provide an overview of various types of community interactions between oral streptococci and other microorganisms, and we consider the possibilities for the development of new technologies to interfere with these interactions to help control oral biofilms.

The pathogenicity of the Streptococcus genus

Streptococcus infections are still one of the important problems facing contemporary medicine. As the World Health Organization (WHO) warns, Streptococcus pneumoniae is responsible for the highest number of pneumonia cases all over the world. Despite an increasing number of pneumococcal vaccinations, incidences of disease connected to this pathogen's infection stay at the same level, which is related to a constantly increasing number of infections caused by nonvaccinal serotypes. Unfortunately, the pathogenicity of bacteria of the Streptococcus genus is also connected to species considered to be physiological flora in humans or animals and, additionally, new species exhibiting pathogenic potential have been discovered. This paper presents an opinion concerning the epidemiology of streptococci infections based on case studies and other publications devoted to this problem. It also sheds new light based on recent reports on the prevention of protective vaccinations application in the case of streptococci infections.

Organo-selenium-containing dental sealant inhibits bacterial biofilm

Oral bacteria, including Streptococcus mutans and Streptococcus salivarius, contribute to tooth decay and plaque formation; therefore, it is essential to develop strategies to prevent dental caries and plaque formation. We recently showed that organo-selenium compounds covalently attached to different biomaterials inhibited bacterial biofilms. Our current study investigates the efficacy of an organo-selenium dental sealant (SeLECT-Defense(TM) sealant) in inhibiting S. mutans and S. salivarius biofilm formation in vitro. The organo-selenium was synthesized and covalently attached to dental sealant material via standard polymer chemistry. By colony-forming unit (CFU) assay and confocal microscopy, SeLECT-Defense(TM) sealant was found to completely inhibit the development of S. mutans and S. salivarius biofilms. To assess the durability of the anti-biofilm effect, we soaked the SeLECT-Defense(TM) sealant in PBS for 2 mos at 37°C and found that the biofilm-inhibitory effect was not diminished after soaking. To determine if organo-selenium inhibits bacterial growth under the sealant, we placed SeLECT-Defense sealant over a lawn of S. mutans. In contrast to a control sealant, SeLECT-Defense(TM) sealant completely inhibited the growth of S. mutans. These results suggest that the inhibitory effect of SeLECT-Defense(TM) sealant against S. mutans and S. salivarius biofilms is very effective and durable.

Multi-species biofilms: how to avoid unfriendly neighbors

Multi-species biofilm communities are environments in which complex but ill understood exchanges between bacteria occur. Although monospecies cultures are still widely used in the laboratory, new approaches have been undertaken to study interspecies interactions within mixed communities. This review describes our current understanding of competitive relationships involving nonbiocidal biosurfactants, enzymes, and metabolites produced by bacteria and other microorganisms. These molecules target all steps of biofilm formation, ranging from inhibition of initial adhesion to matrix degradation, jamming of cell-cell communications, and induction of biofilm dispersion. This review presents available data on nonbiocidal molecules and provides a new perspective on competitive interactions within biofilms that could lead to antibiofilm strategies of potential biomedical interest.

Roles of salivary components in Streptococcus mutans colonization in a new animal model using NOD/SCID.e2f1-/- mice

Streptococcus mutans plays an important role in biofilm formation on the tooth surface and is the primary causative agent of dental caries. The binding of S. mutans to the salivary pellicle is of considerable etiologic significance and is important in biofilm development. Recently, we produced NOD/SCID.e2f1(-/-) mice that show hyposalivation, lower salivary antibody, and an extended life span compared to the parent strain: NOD.e2f1(-/-). In this study we used NOD/SCID.e2f1(-/-) 4 or 6 mice to determine the roles of several salivary components in S. mutans colonization in vivo. S. mutans colonization in NOD/SCID.e2f1(-/-) mice was significantly increased when mice were pre-treated with human saliva or commercial salivary components. Interestingly, pre-treatment with secretory IgA (sIgA) at physiological concentrations promoted significant colonization of S. mutans compared with sIgA at higher concentrations, or with human saliva or other components. Our data suggest the principal effects of specific sIgA on S. mutans occur during S. mutans colonization, where the appropriate concentration of specific sIgA may serve as an anti-microbial agent, agglutinin, or an adherence receptor to surface antigens. Further, specific sIgA supported biofilm formation when the mice were supplied 1% sucrose water and a non-sucrose diet. The data suggests that there are multiple effects exerted by sIgA in S. mutans colonization, with synergistic effects evident under the condition of sIgA and limited nutrients on colonization in NOD/SCID.e2f1(-/-) mice. This is a new animal model that can be used to assess prevention methods for dental biofilm-dependent diseases such as dental caries.

The Pst system of Streptococcus mutans is important for phosphate transport and adhesion to abiotic surfaces

The Pst system is a high-affinity inorganic phosphate transporter found in many bacterial species. Streptococcus mutans, the etiological agent of tooth decay, carries a single copy of the pst operon composed of six cistrons (pstS, pstC1, pstC, pstB, smu.1134 and phoU). Here, we show that deletion of pstS, encoding the phosphate-binding protein, reduces phosphate uptake and impairs cell growth, which can be restored upon enrichment of the medium with high concentrations of inorganic phosphate. The relevance of Pst for growth was also demonstrated in the wild-type strain treated with an anti-PstS antibody. Nevertheless, a reduced ability to bind to saliva-coated surfaces was observed, along with the reduction of extracellular polysaccharide production, although no difference on pH acidification was observed between mutant and wild-type strains. Taken together, the present data indicate that the S. mutans Pst system participates in phosphate uptake, cell growth and expression of virulence-associated traits.

Effect of Streptococcus salivarius K12 on the in vitro growth of Candida albicans and its protective effect in an oral candidiasis model

Oral candidiasis is often accompanied by severe inflammation, resulting in a decline in the quality of life of immunosuppressed individuals and elderly people. To develop a new oral therapeutic option for candidiasis, a nonpathogenic commensal oral probiotic microorganism, Streptococcus salivarius K12, was evaluated for its ability to modulate Candida albicans growth in vitro, and its therapeutic activity in an experimental oral candidiasis model was tested. In vitro inhibition of mycelial growth of C. albicans was determined by plate assay and fluorescence microscopy. Addition of S. salivarius K12 to modified RPMI 1640 culture medium inhibited the adherence of C. albicans to the plastic petri dish in a dose-dependent manner. Preculture of S. salivarius K12 potentiated its inhibitory activity for adherence of C. albicans. Interestingly, S. salivarius K12 was not directly fungicidal but appeared to inhibit Candida adhesion to the substratum by preferentially binding to hyphae rather than yeast. To determine the potentially anti-infective attributes of S. salivarius K12 in oral candidiasis, the probiotic was administered to mice with orally induced candidiasis. Oral treatment with S. salivarius K12 significantly protected the mice from severe candidiasis. These findings suggest that S. salivarius K12 may inhibit the process of invasion of C. albicans into mucous surfaces or its adhesion to denture acrylic resins by mechanisms not associated with the antimicrobial activity of the bacteriocin. S. salivarius K12 may be useful as a probiotic as a protective tool for oral care, especially with regard to candidiasis.