Plausible Drug Targets in the Streptococcus mutans Quorum Sensing Pathways to Combat Dental Biofilms and Associated Risks

Pharmacoinformatics-Based Approach for Uncovering the Quorum-Quenching Activity of Phytocompounds against the Oral Pathogen, Streptococcus mutans

Streptococcus mutans, a gram-positive oral pathogen, is the primary causative agent of dental caries. Biofilm formation, a critical characteristic of S. mutans, is regulated by quorum sensing (QS). This study aimed to utilize pharmacoinformatics techniques to screen and identify effective phytochemicals that can target specific proteins involved in the quorum sensing pathway of S. mutans. A computational approach involving homology modeling, model validation, molecular docking, and molecular dynamics (MD) simulation was employed. The 3D structures of the quorum sensing target proteins, namely SecA, SMU1784c, OppC, YidC2, CiaR, SpaR, and LepC, were modeled using SWISS-MODEL and validated using a Ramachandran plot. Metabolites from Azadirachta indica (Neem), Morinda citrifolia (Noni), and Salvadora persica (Miswak) were docked against these proteins using AutoDockTools. MD simulations were conducted to assess stable interactions between the highest-scoring ligands and the target proteins. Additionally, the ADMET properties of the ligands were evaluated using SwissADME and pkCSM tools. The results demonstrated that campesterol, meliantrol, stigmasterol, isofucosterol, and ursolic acid exhibited the strongest binding affinity for CiaR, LepC, OppC, SpaR, and Yidc2, respectively. Furthermore, citrostadienol showed the highest binding affinity for both SMU1784c and SecA. Notably, specific amino acid residues, including ASP86, ARG182, ILE179, GLU143, ASP237, PRO101, and VAL84 from CiaR, LepC, OppC, SecA, SMU1784c, SpaR, and YidC2, respectively, exhibited significant interactions with their respective ligands. While the docking study indicated favorable binding energies, the MD simulations and ADMET studies underscored the substantial binding affinity and stability of the ligands with the target proteins. However, further in vitro studies are necessary to validate the efficacy of these top hits against S. mutans.

Association of polymicrobial interactions with dental caries development and prevention

Dental caries is a common oral disease. In many cases, disruption of the ecological balance of the oral cavity can result in the occurrence of dental caries. There are many cariogenic microbiota and factors, and their identification allows us to take corresponding prevention and control measures. With the development of microbiology, the caries-causing bacteria have evolved from the traditional single Streptococcus mutans to the discovery of oral symbiotic bacteria. Thus it is necessary to systematically organized the association of polymicrobial interactions with dental caries development. In terms of ecology, caries occurs due to an ecological imbalance of the microbiota, caused by the growth and reproduction of cariogenic microbiota due to external factors or the disruption of homeostasis by one's own factors. To reduce the occurrence of dental caries effectively, and considering the latest scientific viewpoints, caries may be viewed from the perspective of ecology, and preventive measures can be taken; hence, this article systematically summarizes the prevention and treatment of dental caries from the aspects of ecological perspectives, in particular the ecological biofilm formation, bacterial quorum sensing, the main cariogenic microbiota, and preventive measures.

Recent Approaches for Downplaying Antibiotic Resistance: Molecular Mechanisms

Antimicrobial resistance (AMR) is a ubiquitous public health menace. AMR emergence causes complications in treating infections contributing to an upsurge in the mortality rate. The epidemic of AMR in sync with a high utilization rate of antimicrobial drugs signifies an alarming situation for the fleet recovery of both animals and humans. The emergence of resistant species calls for new treatments and therapeutics. Current records propose that health drug dependency, veterinary medicine, agricultural application, and vaccination reluctance are the primary etymology of AMR gene emergence and spread. Recently, several encouraging avenues have been presented to contest resistance, such as antivirulent therapy, passive immunization, antimicrobial peptides, vaccines, phage therapy, and botanical and liposomal nanoparticles. Most of these therapies are used as cutting-edge methodologies to downplay antibacterial drugs to subdue the resistance pressure, which is a featured motive of discussion in this review article. AMR can fade away through the potential use of current cutting-edge therapeutics, advancement in antimicrobial susceptibility testing, new diagnostic testing, prompt clinical response, and probing of new pharmacodynamic properties of antimicrobials. It also needs to promote future research on contemporary methods to maintain host homeostasis after infections caused by AMR. Referable to the microbial ability to break resistance, there is a great ultimatum for using not only appropriate and advanced antimicrobial drugs but also other neoteric diverse cutting-edge therapeutics.

Natural products from traditional medicine as promising agents targeting at different stages of oral biofilm development

Oral cavity is an ideal habitat for more than 1,000 species of microorganisms. The diverse oral microbes form biofilms over the hard and soft tissues in the oral cavity, affecting the oral ecological balance and the development of oral diseases, such as caries, apical periodontitis, and periodontitis. Currently, antibiotics are the primary agents against infectious diseases; however, the emergence of drug resistance and the disruption of oral microecology have challenged their applications. The discovery of new antibiotic-independent agents is a promising strategy against biofilm-induced infections. Natural products from traditional medicine have shown potential antibiofilm activities in the oral cavity with high safety, cost-effectiveness, and minimal adverse drug reactions. Aiming to highlight the importance and functions of natural products from traditional medicine against oral biofilms, here we summarized and discussed the antibiofilm effects of natural products targeting at different stages of the biofilm formation process, including adhesion, proliferation, maturation, and dispersion, and their effects on multi-species biofilms. The perspective of antibiofilm agents for oral infectious diseases to restore the balance of oral microecology is also discussed.

Plant-Derived Substances with Antibacterial, Antioxidant, and Flavoring Potential to Formulate Oral Health Care Products

Bacterial diseases and reactive oxygen species can cause dental caries and oral cancer. Therefore, the present review analyzes and discusses the antibacterial and antioxidant properties of synthetic and plant-derived substances and their current and future patents to formulate dental products. The reviewed evidence indicates that chlorhexidine, fluorides, and hydrogen peroxide have adverse effects on the sensory acceptability of oral care products. As an alternative, plant-derived substances have antimicrobial and antioxidant properties that can be used in their formulation. Also, adding plant metabolites favors the sensory acceptability of dental products compared with synthetic compounds. Therefore, plant-derived substances have antibacterial, antioxidant, and flavoring activity with the potential to be used in the formulation of toothpaste, mouth rinses, dentures cleansers-fixatives, and saliva substitutes.

Antimicrobial and Antibiofilm Activity of Curcumin-Loaded Electrospun Nanofibers for the Prevention of the Biofilm-Associated Infections

Curcumin extracted from the rhizome of Curcuma Longa has been used in therapeutic preparations for centuries in different parts of the world. However, its bioactivity is limited by chemical instability, water insolubility, low bioavailability, and extensive metabolism. In this study, the coaxial electrospinning technique was used to produce both poly (ε-caprolactone) (PCL)-curcumin and core-shell nanofibers composed of PCL and curcumin in the core and poly (lactic acid) (PLA) in the shell. Morphology and physical properties, as well as the release of curcumin were studied and compared with neat PCL, showing the formation of randomly oriented, defect-free cylindrical fibers with a narrow distribution of the dimensions. The antibacterial and antibiofilm potential, including the capacity to interfere with the quorum-sensing mechanism, was evaluated on Pseudomonas aeruginosa PAO1, and Streptococcus mutans, two opportunistic pathogenic bacteria frequently associated with infections. The reported results demonstrated the ability of the Curcumin-loading membranes to inhibit both PAO1 and S. mutans biofilm growth and activity, thus representing a promising solution for the prevention of biofilm-associated infections. Moreover, the high biocompatibility and the ability to control the oxidative stress of damaged tissue, make the synthesized membranes useful as scaffolds in tissue engineering regeneration, helping to accelerate the healing process.

Biofilm inhibition in oral pathogens by nanodiamonds

Complex microbial communities, e.g., biofilms residing in our oral cavity, have recognized clinical significance, as they are typically the main cause for infections. Particularly, they show high resistance to conventional antibiotics, and alternatives including nanotechnology are being intensively explored nowadays to provide more efficient therapeutics. Diamond nanoparticles, namely, nanodiamonds (NDs) with many promising physico-chemical properties, have been demonstrated to work as an effective antibacterial agent against planktonic cells (free-floating state). However, little is known about the behaviors of NDs against biofilms (sessile state). In this study, we uncovered their role in inhibiting biofilm formation and their disrupting effect on preformed biofilms in several selected orally and systemically important organisms. The current findings will advance the mechanistic understanding of NDs on oral pathogens and might accelerate corresponding clinical translation.

Visible light-induced antibacterial and osteogenic cell proliferation properties of hydrogenated TiO2 nanotubes/Ti foil composite

We successfully fabricated the hydrogenated TiO₂ nanotubes/Ti foil (H-TNTs/f-Ti) composite via one-step anodization and two-step annealing. H-TNTs/f-Ti composite had a higher visible light-induced photoelectric response and more hydroxyl functional groups compared with Ti foil and unmodified TiO₂ nanotubes/Ti foil composite, which contributed to limiting the proliferation of Streptococcus mutans and Porphyromonas gingivalis, promoting the proliferation of MC3T3-E1 cell on the hydroxylated surface, and improving the biocompatibility with osteogenic cells. Our study provides a simple and effective method for significantly improving dental implant efficacy.

Inhibition of Streptococcus mutans biofilm formation by strategies targeting the metabolism of exopolysaccharides

Dental caries is one of the most prevalent and costly biofilm-associated infectious diseases affecting most of the world's population. In particular, dental caries is driven by dysbiosis of the dental biofilm adherent to the enamel surface. Specific types of acid-producing bacteria, especially Streptococcus mutans, colonize the dental surface and cause damage to the hard tooth structure in the presence of fermentable carbohydrates. Streptococcus mutans has been established as the major cariogenic pathogen responsible for human dental caries, with a high ability to form biofilms. The exopolysaccharide (EPS) matrix, mainly contributed by S. mutans, has been considered as a virulence determinant of cariogenic biofilm. As EPS is an important virulence factor, targeting EPS metabolism could be useful in preventing cariogenic biofilm formation. This review summarizes plausible strategies targeting S. mutans biofilms by degrading EPS structure, inhibiting EPS production, and disturbing the EPS metabolism-related gene expression and regulatory systems.

Exploring the anti-caries properties of baicalin against Streptococcus mutans: an in vitro study

Plant-derived molecules are excellent alternatives to antibiotics as anti-infective agents owing to their minimal cytotoxicity. Herein, the anti-infective property of the hydroxyflavone baicalin, was investigated against biofilms of the key dental caries pathogen Streptococcus mutans. Baicalin inhibited sucrose-dependent biofilm formation at a concentration of 500 µg ml^-1 without affecting bacterial growth. It significantly inhibited acid production for an extended period of 8 h. Microscopic analysis revealed a 6-fold reduction in the number of adhered cells with baicalin treatment. Transcriptomic analysis of the mid-log phase and biofilm cells showed marked downregulation of the virulence genes required for biofilm formation and acid production. This study sheds significant new light on the potential for baicalin to be developed into an anti-caries agent.

Baicalein Inhibits Streptococcus mutans Biofilms and Dental Caries-Related Virulence Phenotypes

Dental caries, the most common oral disease, is a major public healthcare burden and affects more than three billion people worldwide. The contemporary understanding of the need for a healthy microbiome and the emergence of antimicrobial resistance has resulted in an urgent need to identify compounds that curb the virulence of pathobionts without microbial killing. Through this study, we have demonstrated for the first time that 5,6,7-trihydroxyflavone (Baicalein) significantly downregulates crucial caries-related virulence phenotypes in Streptococcus mutans. Baicalein significantly inhibited biofilm formation by Streptococcus mutans UA159 (MBIC50 = 200 μM), without significant growth inhibition. Notably, these concentrations of baicalein did not affect the commensal S. gordonii. Strikingly, baicalein significantly reduced cell surface hydrophobicity, autoaggregation and acid production by S. mutans. Mechanistic studies (qRT-PCR) showed downregulation of various genes regulating biofilm formation, surface attachment, quorum sensing, acid production and competence. Finally, we demonstrate the potential translational value of baicalein by reporting synergistic interaction with fluoride against S. mutans biofilms.

Analysis of multidrug resistance in Streptococcus suis ATCC 700794 under tylosin stress

Streptococcus suis is an important zoonotic pathogen. The massive use of tylosin and other antibiotics in swine production has led to the emergence of resistant phenotypes of S. suis. However, there are no adequate measures available to address the problem of bacterial resistance. This study involved the use of 1/4 MIC (0.125 µg/mL) of tylosin to investigate resistance-related proteins by S. suis ATCC 700794. Our results showed that 171 proteins were differentially expressed in S. suis tested with 1/4 MIC (0.125 µg/mL) of tylosin using iTRAQ-based quantitative proteomic methods. TCS, heat shock protein and elongation factors were differentially expressed at 1/4 MIC (0.125 µg/mL) of tylosin compared to non treated, control cells. Using quantitative RT-PCR analysis, we verified the relationship between the differentially expressed proteins in S. suis with different MIC values. The data showed that expression profile for elongation factor G (fusA), elongation factor Ts (tsf), elongation factor Tu (tuf), putative histidine kinase of the competence regulon, ComD (comD), putative competence-damage inducible protein (cinA) and protein GrpE (grpE), observed in tylosin-resistant S. suis, correlated with that of S. suis ATCC 700794 at 1/4 MIC (0.125 µg/mL). The MIC of tylosin-resistant showed high-level resistance in terramycin, chlortetracycline, ofloxacin and enrofloxacin. Our findings demonstrated the importance of elongation factors, TCS and heat shock protein during development of tylosin resistance in S. suis. Thus, our study will provide insight into new drug targets and help reduce bacterial multidrug resistance through development of corresponding inhibitors.

Guardian genes ensuring subsistence of oral Streptococcus mutans

Despite the substantial research advancements on oral diseases, dental caries remains a major healthcare burden. A disease of microbial dysbiosis, dental caries is characterised by the formation of biofilms that assist demineralisation and destruction of the dental hard tissues. While it is well understood that this is a multi-kingdom biofilm-mediated disease, it has been elucidated that acid producing and acid tolerant bacteria play pioneering roles in the process. Specifically, Streptococcus mutans houses major virulence pathways that enable it to thrive in the oral cavity and cause caries. This pathogen adheres to the tooth substrate, forms biofilms, resists external stress, produces acids, kills closely related species, and survives the acid as well as the host clearance mechanisms. For an organism to be able to confer such virulence, it requires a large and complex gene network which synergise to establish disease. In this review, we have charted how these multi-faceted genes control several caries-related functions of Streptococcus mutans. In a futuristic thinking approach, we also briefly discuss the potential roles of omics and machine learning, to ease the study of non-functional genes that may play a major role and enable the integration of experimental data.

Bacterial Populations in Subgingival Plaque Under Healthy and Diseased Conditions: Genomic Insights into Oral Adaptation Strategies by Lactobacillus sp. Strain DISK7

Human oral cavity is a complex habitat comprising about 700 microbial species and represents the most complex microbiota after gastrointestinal tract. In fact, oral microbiota directly influences health, metabolism and immune responses of the host. Metagenomic studies based on 16S rDNA profiling has reported the inhabitant bacteria mainly belonging to phyla Firmicutes, Proteobacteria, Actinobacteria, Fusobacteria, Spirochaetes and Bacteroidetes. Therefore, it is essential to isolate these strains and characterize in detail to understand their interaction. We have isolated strains from subgingival plaque from healthy to diseased individuals and the molecular characterization based on 16S rRNA gene sequence analysis showed predominance of Firmicutes, specifically members of the genus Streptococcus. Species of Lactobacillus and Veillonella were also found in significant number, which are considered as secondary colonizers. However, the population of Lactobacillus was decreased in diseased conditions with the increase in opportunistic pathogenic strains pertaining to genera like Campylobacter, Neisseria, Enterobacter, Pseudomonas and Morococcus. Further, we have also made an attempt to gain genomic insights on adaptation features and interactions of an isolate, Lactobacillus sp. strain DISK7 by performing whole genome sequencing and analysis, subsequently biochemical characterization to explore its functional and metabolic properties for the development as probiotic agent.

Use of d-galactose to regulate biofilm growth of oral streptococci

In the oral microbial community, commensals can compete with pathogens and reduce their colonization in the oral cavity. A substance that can inhibit harmful bacteria and enrich beneficial bacteria is required to maintain oral health. The purpose of this study was to examine the effect of d-galactose on the biofilm formation of the cariogenic bacteria Streptococcus mutans and oral commensal streptococci and to evaluate their use in solution and in paste form. Biofilms of S. mutans, Streptococcus oralis, and Streptococcus mitis were formed on saliva-coated glass slips in the absence or presence of d-galactose and evaluated by staining with 1 % crystal violet. d-Galactose significantly inhibited the biofilm formation of S. mutans at concentrations ranging from 2 μM to 200 mM but increased the biofilm formation of S. oralis and S. mitis at concentrations of 2-200 mM. d-Galactose significantly inhibited three glucosyltransferase genes, gtfB, gtfC, and gtfD. The effect of d-galactose in the form of solution and paste was evaluated using bovine teeth. Pretreatment with 100 mM d-galactose on bovine teeth resulted in significantly reduced S. mutans biofilm formation. Our results suggest that d-galactose can be a candidate substance for the development of oral hygiene products to prevent caries by inhibiting the biofilm formation of S. mutans and simultaneously increasing the biofilm formation of commensal oral streptococci.

An overview on anti-biofilm properties of quercetin against bacterial pathogens

Bacterial biofilms are multicellular aggregates enclosed in a self-created biopolymer matrix. Biofilm-producing bacteria have become a great public health problem worldwide because biofilms enable these microorganisms to evade several clearance mechanisms produced by host and synthetic sources. Over the past years, different flavonoids including quercetin have engrossed considerable interest among researchers owing to their potential anti-biofilm properties. To our knowledge, there is no review regarding effects of quercetin towards bacterial biofilms, prompting us to summarize experimental evidence on its anti-biofilm properties. Quercetin inhibits biofilm development by a diverse array of bacterial pathogens such as Enterococcus faecalis, Staphylococcus aureus, Streptococcus mutans, Escherichia coli, and Pseudomonas aeruginosa. Prevention of bacterial adhesion, suppression of quorum-sensing pathways, disruption or alteration of plasma membrane, inhibition of efflux pumps, and blocking nucleic acid synthesis have been documented as major anti-biofilm mechanisms of quercetin. Overall, anti-biofilm activity of quercetin can open up new horizons in a wide range of biomedical areas, from food industry to medicine.

Insight into the Effect of Small RNA srn225147 on Mutacin IV in Streptococcus mutans

Streptococcus mutans (S. mutans) is a serious microbe causing dental caries. Mutacin IV is an effective bacteriocin produced by S. mutans to antagonize numerous non-mutans streptococcal species. However, the posttranscriptional regulation of mutacin IV remains unclear. This study aimed to analyze the effect of small RNA srn225147 on mutacin IV. The functional prediction suggested that srn225147 is involved in the production of mutacin IV, an important secondary metabolite. According to RNAhybrid and RNAPredator prediction, the mutacin IV formation-associated gene comD is a target of srn225147. We further analyzed the roles of srn225147 and comD in 20 S. mutans clinical strains with high production of mutacin IV (High-IV group) and lacking mutacin IV (None-IV group). Levels of comD expression were significantly higher in the High-IV group, whereas the Non-IV group showed relatively higher expression of srn225147, with a negative correlation observed between srn225147 and comD. Moreover, compared to the mimic negative control (NC) group, comD expression was decreased at 400-fold srn225147 overexpression but increased at approximately 1400-fold overexpression. Although the production of mutacin IV in the 1400-fold change srn225147 mimic group was larger than that in the 400-fold change mimic group, there was no significant difference in the production of mutacin IV between the srn225147 mimic group and mimic NC group. These results indicate that srn225147 has a two-way regulation effect on the expression of comD but that its regulation in the production of mutacin IV is weak.

Deletion of cas3 gene in Streptococcus mutans affects biofilm formation and increases fluoride sensitivity

OBJECTIVE

The goal of this study was to analyze the impact of cas3 gene on the biofilm formation and virulence gene expression in S. mutans, since our previous studies have found a connection between CRISPR/Cas systems and biofilm formation in S. mutans.

METHODS

The cas3 gene in-frame deletion strains of S. mutans UA159 was constructed by a two-step transformation procedure and the cas3 mutant strain was complemented in trans. The biofilm biomass was measured by crystal violet staining, and the synthesis of exopolysaccharides (EPS) was measured by the anthrone-sulfuric method. Biofilm analysis and structural imaging was using confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM) assays. The fluorescence in situ hybridization (FISH) was used to analyze the spatiotemporal interactions between S. mutans and Streptococcus sanguinis. Fluoride sensitivity was determined using fluoride tolerance assays. The expression of biofilm formation related genes was evaluated by qRT-PCR.

RESULTS

Our results showed that S. mutans cas3 deletion strain formed less biofilm and became less competitive when it was co-cultured with S. sanguinis under fluoride treatment. The expression levels of virulence genes including vicR, gtfC, smu0630 and comDE were significantly downregulated.

CONCLUSIONS

The cas3 gene in S. mutans could regulate biofilm formation and fluoride resistance, consequently affecting S. mutans competitiveness in a dual-species biofilm model under fluoride treatment. These results also provide a potential strategy for enhancing fluoride specificity, with cas3 gene as a potential genetic target in the modulation of oral microecology and the treatment of dental caries.

Determination and identification of antibiotic-resistant oral streptococci isolated from active dental infections in adults

OBJECTIVE

To determine and identify antibiotic-resistant bacteria (ARB) of oral streptococci from active dental infections in adults and its association with age and gender.

MATERIAL AND METHODS

This cross-sectional study included 59 subjects from 18 to 62 years old. Ninety-eighth samples obtained from the subjects were cultivated in agar plates containing antibiotics amoxicillin/clavulanic acid (A-CA), clindamycin, and moxifloxacin (concentrations of 16, 32 or 64 µg/ml). PCR assay was performed to identify bacterial species.

RESULTS

The bacterial species that showed more antibiotic-resistance (AR) was S. mutans (45.9%), followed by S. gordonii (21.6%), S. oralis (17.6%), S. sanguinis (9.5%), S. salivarius (5.4%) and S. sobrinus (0%). Moreover, clindamycin (59.4%) showed the highest frequency of AR. Moxifloxacin and A-CA showed an susceptibility >99.1%, while clindamycin showed the lowest efficacy (93.3%); there was a significant statistically difference (p < .01). The age group between 26 and 50 years old (32.2%) and females (28.8%) showed more multiresistance. Clindamycin showed a statistical difference (p < .05) when comparing groups by gender.

CONCLUSIONS

Clindamycin was the antibiotic with the highest frequency of ARB and lower bactericidal effect. Moxifloxacin and A-CA showed the highest efficacy and the lowest ARB frequency. Streptococcus mutans was the bacterial specie that showed an increased frequency of AR.

Anti-biofilm Activities from Bergenia crassifolia Leaves against Streptococcus mutans

Streptococcus mutans has been reported as a primary cariogenic pathogen associated with dental caries. The bacteria can produce glucosyltransferases (Gtfs) to synthesize extracellular polysaccharides (EPSs) that are known as virulence factors for adherence and formation of biofilms. Therefore, an ideal inhibitor for dental caries is one that can inhibit planktonic bacteria growth and prevent biofilm formation. Bergenia crassifolia (L.), widely used as a folk medicine and tea beverage, has been reported to have a variety of bioactivities. The present study aimed to explore the effect of B. crassifolia (L.) leaf extracts on the biofilm of Streptococcus mutans. The B. crassifolia (L.) leaf extracts showed inhibitory effects by decreasing viability of bacteria within the biofilm, as evidenced by the XTT assay, live/dead staining assay and LDH activity assay, and could decrease the adherence property of S. mutans through inhibiting Gtfs to synthesize EPSs. In addition, the reduced quantity of EPSs and the inhibition of Gtfs were positively correlated with concentrations of test samples. Finally, the MTT assay showed that the extracts had no cytotoxicity against normal oral cells. In conclusion, the extracts and sub-extracts of B. crassifolia leaves were found to be antimicrobial and could reduce EPS synthesis by inhibiting activities of Gtfs to prevent bacterial adhesion and biofilm formation. Therefore, B. crassifolia leaves have potential to be developed as a drug to prevent and cure dental caries.

Inhibition of the Quorum Sensing System (ComDE Pathway) by Aromatic 1,3-di-m-tolylurea (DMTU): Cariostatic Effect with Fluoride in Wistar Rats

Dental caries occurs as a result of dysbiosis among commensal and pathogenic bacteria leading to demineralization of enamel within a dental biofilm (plaque) as a consequence of lower pH in the oral cavity. In our previous study, we have reported 1,3-disubstituted ureas particularly, 1,3-di-m-tolylurea (DMTU) could inhibit the biofilm formation along with lower concentrations of fluoride (31.25 ppm) without affecting bacterial growth. In the present study, RT-qPCR analysis showed the target specific molecular mechanism of DMTU. In vivo treatment with DMTU, alone or in combination with fluoride, resulted in inhibition of caries (biofilm development of Streptococcus mutans) using a Wistar rat model for dental caries. The histopathological analysis reported the development of lesions on dentine in infected subjects whereas the dentines of treated rodents were found to be intact and healthy. Reduction in inflammatory markers in rodents' blood and liver samples was observed when treated with DMTU. Collectively, data speculate that DMTU is an effective anti-biofilm and anti-inflammatory agent, which may improve the cariostatic properties of fluoride.

Antibiotics and specialized metabolites from the human microbiota

Human microbiota associated with each body site produce specialized molecules to kill human pathogens. Advanced bioinformatics tools will help to discover unique microbiome chemistry.

Multiplicity of Quorum Quenching Enzymes: A Potential Mechanism to Limit Quorum Sensing Bacterial Population

Bacteria express certain of their characteristics especially, pathogenicity factors at high cell densities. The process is termed as quorum sensing (QS). QS operates via signal molecules such as acylhomoserine lactones (AHLs). Other bacteria inhibit QS through the inactivation of AHL signals by producing enzymes like AHL-lactonases and -acylases. Comparative genomic analysis has revealed the multiplicity of genes for AHL lactonases (up to 12 copies per genome) among Bacillus spp. and that of AHL-acylases (up to 5 copies per genome) among Pseudomonas spp. This genetic evolution can be envisaged to enable host to withstand the attacks from bacterial population, which regulates its functioning through QS.

Insights in Waste Management Bioprocesses Using Genomic Tools

Microbial capacities drive waste stabilization and resource recovery in environmental friendly processes. Depending on the composition of waste, a stress-mediated selection process ensures a scenario that generates a specific enrichment of microbial community. These communities dynamically change over a period of time while keeping the performance through the required utilization capacities. Depending on the environmental conditions, these communities select the appropriate partners so as to maintain the desired functional capacities. However, the complexities of these organizations are difficult to study. Individual member ratios and sharing of genetic intelligence collectively decide the enrichment and survival of these communities. The next-generation sequencing options with the depth of structure and function analysis have emerged as a tool that could provide the finer details of the underlying bioprocesses associated and shared in environmental niches. These tools can help in identification of the key biochemical events and monitoring of expression of associated phenotypes that will support the operation and maintenance of waste management systems. In this chapter, we link genomic tools with process optimization and/or management, which could be applied for decision making and/or upscaling. This review describes both, the aerobic and anaerobic, options of waste utilization process with the microbial community functioning as flocs, granules, or biofilms. There are a number of challenges involved in harnessing the microbial community intelligence with associated functional plasticity for efficient extension of microbial capacities for resource recycling and waste management. Mismanaged wastes could lead to undesired genotypes such as antibiotic/multidrug-resistant microbes.

Control of Multidrug-Resistant Gene Flow in the Environment Through Bacteriophage Intervention

The spread of multidrug-resistant (MDR) bacteria is an emerging threat to the environment and public wellness. Inappropriate use and indiscriminate release of antibiotics in the environment through un-metabolized form create a scenario for the emergence of virulent pathogens and MDR bugs in the surroundings. Mechanisms underlying the spread of resistance include horizontal and vertical gene transfers causing the transmittance of MDR genes packed in different host, which pass across different food webs. Several controlling agents have been used for combating pathogens; however, the use of lytic bacteriophages proves to be one of the most eco-friendly due to their specificity, killing only target bacteria without damaging the indigenous beneficial flora of the habitat. Phages are part of the natural microflora present in different environmental niches and are remarkably stable in the environment. Diverse range of phage products, such as phage enzymes, phage peptides having antimicrobial properties, and phage cocktails also have been used to eradicate pathogens along with whole phages. Recently, the ability of phages to control pathogens has extended from the different areas of medicine, agriculture, aquaculture, food industry, and into the environment. To avoid the arrival of pre-antibiotic epoch, phage intervention proves to be a potential option to eradicate harmful pathogens generated by the MDR gene flow which are uneasy to cure by conventional treatments.

Simple and Rapid Method for Detecting Biofilm Forming Bacteria

Biofilm forming bacteria play a vital role in causing infectious diseases and for enhancing the efficiency of the bioremediation process through immobilization. Different media and conditions have been reported for detecting biofilm forming bacteria, however, they are not quite rapid. Here, we propose the use of a simple medium which can be used for detecting biofilm former, and also provide a mechanism to regulate the expression of biofilm formation process.

Combinatorial Effects of Aromatic 1,3-Disubstituted Ureas and Fluoride on In vitro Inhibition of Streptococcus mutans Biofilm Formation

Dental caries occur as a result of disequilibrium between acid producing pathogenic bacteria and alkali generating commensal bacteria within a dental biofilm (dental plaque). Streptococcus mutans has been reported as a primary cariogenic pathogen associated with dental caries. Emergence of multidrug resistant as well as fluoride resistant strains of S. mutans due to over use of various antibiotics are a rising problem and prompted the researchers worldwide to search for alternative therapies. In this perspective, the present study was aimed to screen selective inhibitors against ComA, a bacteriocin associated ABC transporter, involved in the quorum sensing of S. mutans. In light of our present in silico findings, 1,3-disubstituted urea derivatives which had better affinity to ComA were chemically synthesized in the present study for in vitro evaluation of S. mutans biofilm inhibition. The results revealed that 1,3-disubstituted urea derivatives showed good biofilm inhibition. In addition, synthesized compounds exhibited potent synergy with a very low concentration of fluoride (31.25-62.5 ppm) in inhibiting the biofilm formation of S. mutans without affecting the bacterial growth. Further, the results were supported by confocal laser scanning microscopy. On the whole, from our experimental results we conclude that the combinatorial application of fluoride and disubstituted ureas has a potential synergistic effect which has a promising approach in combating multidrug resistant and fluoride resistant S. mutans in dental caries management.

Molecular Mechanisms of Inhibition of Streptococcus Species by Phytochemicals

This review paper summarizes the antibacterial effects of phytochemicals of various medicinal plants against pathogenic and cariogenic streptococcal species. The information suggests that these phytochemicals have potential as alternatives to the classical antibiotics currently used for the treatment of streptococcal infections. The phytochemicals demonstrate direct bactericidal or bacteriostatic effects, such as: (i) prevention of bacterial adherence to mucosal surfaces of the pharynx, skin, and teeth surface; (ii) inhibition of glycolytic enzymes and pH drop; (iii) reduction of biofilm and plaque formation; and (iv) cell surface hydrophobicity. Collectively, findings from numerous studies suggest that phytochemicals could be used as drugs for elimination of infections with minimal side effects.

Potential Emergence of Multi-quorum Sensing Inhibitor Resistant (MQSIR) Bacteria

Expression of certain bacterial genes only at a high bacterial cell density is termed as quorum-sensing (QS). Here bacteria use signaling molecules to communicate among themselves. QS mediated genes are generally involved in the expression of phenotypes such as bioluminescence, biofilm formation, competence, nodulation, and virulence. QS systems (QSS) vary from a single in Vibrio spp. to multiple in Pseudomonas and Sinorhizobium species. The complexity of QSS is further enhanced by the multiplicity of signals: (1) peptides, (2) acyl-homoserine lactones, (3) diketopiperazines. To counteract this pathogenic behaviour, a wide range of bioactive molecules acting as QS inhibitors (QSIs) have been elucidated. Unlike antibiotics, QSIs don't kill bacteria and act at much lower concentration than those of antibiotics. Bacterial ability to evolve resistance against multiple drugs has cautioned researchers to develop QSIs which may not generate undue pressure on bacteria to develop resistance against them. In this paper, we have discussed the implications of the diversity and multiplicity of QSS, in acting as an arsenal to withstand attack from QSIs and may use these as reservoirs to develop multi-QSI resistance.