Inactivation of Streptococcus mutans genes lytST and dltAD impairs its pathogenicity in vivo

Metal-based nanoparticles: an alternative treatment for biofilm infection in hard-to-heal wounds

Metal-based nanoparticles (MNPs) are promoted as effective compounds in the treatment of bacterial infections and as possible alternatives to antibiotics. These MNPs are known to affect a broad spectrum of microorganisms using a multitude of strategies, including the induction of reactive oxygen species and interaction with the inner structures of the bacterial cells. The aim of this review was to summarise the latest studies about the effect of metal-based nanoparticles on pathogenic bacterial biofilm formed in wounds, using the examples of Gram-positive bacterium Staphylococcus aureus and Gram-negative bacterium Pseudomonas aeruginosa, as well as provide an overview of possible clinical applications.

Small regulatory RNAs are mediators of the Streptococcus mutans SloR regulon

Dental caries is among the most prevalent chronic diseases worldwide. Streptococcus mutans, the chief causative agent of caries, uses a 25-kDa manganese-dependent SloR protein to coordinate the uptake of essential manganese with the transcription of its virulence attributes. Small non-coding RNAs (sRNAs) can either enhance or repress gene expression, and reports in the literature ascribe an emerging role for sRNAs in the environmental stress response. Herein, we focused our attention on 18-50 nt sRNAs as mediators of the S. mutans SloR and manganese regulons. Specifically, the results of RNA sequencing revealed 19 sRNAs in S. mutans, which were differentially transcribed in the SloR-proficient UA159 and SloR-deficient GMS584 strains, and 10 sRNAs that were differentially expressed in UA159 cells grown in the presence of low vs high manganese. We describe SmsR1532 and SmsR1785 as SloR- and manganese-responsive sRNAs that are processed from large transcripts and that bind SloR directly in their promoter regions. The predicted targets of these sRNAs include regulators of metal ion transport, growth management via a toxin-antitoxin operon, and oxidative stress tolerance. These findings support a role for sRNAs in coordinating intracellular metal ion homeostasis with virulence gene control in an important oral cariogen. IMPORTANCE Small regulatory RNAs (sRNAs) are critical mediators of environmental signaling, particularly in bacterial cells under stress, but their role in Streptococcus mutans is poorly understood. S. mutans, the principal causative agent of dental caries, uses a 25-kDa manganese-dependent protein, called SloR, to coordinate the regulated uptake of essential metal ions with the transcription of its virulence genes. In the present study, we identified and characterized sRNAs that are both SloR and manganese responsive. Taken together, this research can elucidate the details of regulatory networks that engage sRNAs in an important oral pathogen and that can enable the development of an effective anti-caries therapeutic.

Small regulatory RNAs are mediators of the Streptococcus mutans SloR regulon

Dental caries is among the most prevalent chronic infectious diseases worldwide. Streptococcus mutans , the chief causative agent of caries, uses a 25 kDa manganese dependent SloR protein to coordinate the uptake of essential manganese with the transcription of its virulence attributes. Small non-coding RNAs (sRNAs) can either enhance or repress gene expression and reports in the literature ascribe an emerging role for sRNAs in the environmental stress response. Herein, we identify 18-50 nt sRNAs as mediators of the S. mutans SloR and manganese regulons. Specifically, the results of sRNA-seq revealed 56 sRNAs in S. mutans that were differentially transcribed in the SloR-proficient UA159 and SloR-deficient GMS584 strains, and 109 sRNAs that were differentially expressed in UA159 cells grown in the presence of low versus high manganese. We describe SmsR1532 and SmsR1785 as SloR- and/or manganese-responsive sRNAs that are processed from large transcripts, and that bind SloR directly in their promoter regions. The predicted targets of these sRNAs include regulators of metal ion transport, growth management via a toxin-antitoxin operon, and oxidative stress tolerance. These findings support a role for sRNAs in coordinating intracellular metal ion homeostasis with virulence gene control in an important oral cariogen.

IMPORTANCE

Small regulatory RNAs (sRNAs) are critical mediators of environmental signaling, particularly in bacterial cells under stress, but their role in Streptococcus mutans is poorly understood. S. mutans, the principal causative agent of dental caries, uses a 25 kDa manganese-dependent protein, called SloR, to coordinate the regulated uptake of essential metal ions with the transcription of its virulence genes. In the present study, we identified and characterize sRNAs that are both SloR- and manganese-responsive. Taken together, this research can elucidate the details of regulatory networks that engage sRNAs in an important oral pathogen, and that can enable the development of an effective anti-caries therapeutic.

Dlt operon regulates physiological function and cariogenic virulence in Streptococcus mutans

Streptococcus mutans is one of the major cariogenic pathogens in the oral cavity. The dlt operon is responsible for the process of D-alanylation of lipoteichoic acid and is related to the virulence of S. mutans. The dlt operon contributes to the adhesion, biofilm formation, stress response, interspecies competitiveness and autolysis of S. mutans. In addition, we have summarized the possible regulatory networks of the dlt operon. This review highlights the significant role of the dlt operon in S. mutans and provides new ideas for ecological caries prevention.

Effect of Extracts, Fractions, and Isolated Molecules of Casearia sylvestris to Control Streptococcus mutans Cariogenic Biofilm

The effects of extracts, fractions, and molecules of Casearia sylvestris to control the cariogenic biofilm of Streptococcus mutans were evaluated. First, the antimicrobial and antibiofilm (initial and pre-formed biofilms) in prolonged exposure (24 h) models were investigated. Second, formulations (with and without fluoride) were assessed for topical effects (brief exposure) on biofilms. Third, selected treatments were evaluated via bacterium growth inhibition curves associated with gene expression and scanning electron microscopy. In initial biofilms, the ethyl acetate (AcOEt) and ethanolic (EtOH) fractions from Brasília (BRA/DF; 250 µg/mL) and Presidente Venceslau/SP (Water/EtOH 60:40 and Water/EtOH 40:60; 500 µg/mL) reduced ≥6-logs vs. vehicle. Only the molecule Caseargrewiin F (CsF; 125 µg/mL) reduced the viable cell count of pre-formed biofilms (5 logs vs. vehicle). For topical effects, no formulation affected biofilm components. For the growth inhibition assay, CsF yielded a constant recovery of surviving cells (≅3.5 logs) until 24 h (i.e., bacteriostatic), and AcOEt_BRA/DF caused progressive cell death, without cells at 24 h (i.e., bactericidal). CsF and AcOEt_BRA/DF damaged S. mutans cells and influenced the expression of virulence genes. Thus, an effect against biofilms occurred after prolonged exposure due to the bacteriostatic and/or bactericidal capacity of a fraction and a molecule from C. sylvestris.

The Role of Regulator Catabolite Control Protein A (CcpA) in Streptococcus agalactiae Physiology and Stress Response

Streptococcus agalactiae is a leading cause of infections in neonates. This opportunistic pathogen colonizes the vagina, where it has to cope with acidic pH and hydrogen peroxide produced by lactobacilli. Thus, in the host, this bacterium possesses numerous adaptation mechanisms in which the pleiotropic regulators play a major role. The transcriptional regulator CcpA (catabolite control protein A) has previously been shown to be the major regulator involved in carbon catabolite repression in Gram-positive bacteria but is also involved in other functions. By transcriptomic analysis, we characterized the CcpA-dependent gene regulation in S. agalactiae. Approximately 13.5% of the genome of S. agalactiae depends on CcpA for regulation and comprises genes involved in sugar uptake and fermentation, confirming the role of CcpA in carbon metabolism. We confirmed by electrophoretic mobility shift assays (EMSAs) that the DNA binding site called cis-acting catabolite responsive element (cre) determined for other streptococci was effective in S. agalactiae. We also showed that CcpA is of capital importance for survival under acidic and oxidative stresses and is implicated in macrophage survival by regulating several genes putatively or already described as involved in stress response. Among them, we focused our study on SAK_1689, which codes a putative UspA protein. We demonstrated that SAK_1689, highly downregulated by CcpA, is overexpressed under oxidative stress conditions, this overexpression being harmful for the bacterium in a ΔccpA mutant. IMPORTANCE Streptococcus agalactiae is a major cause of disease burden leading to morbidity and mortality in neonates worldwide. Deciphering its adaptation mechanisms is essential to understand how this bacterium manages to colonize its host. Here, we determined the regulon of the pleiotropic regulator CcpA in S. agalactiae. Our findings reveal that CcpA is not only involved in carbon catabolite repression, but is also important for acidic and oxidative stress resistance and survival in macrophages.

Streptococcus agalactiae cadD Is Critical for Pathogenesis in the Invertebrate Galleria mellonella Model

Group B Streptococcus (GBS) is a gram-positive bacterium that can cause invasive infections in immunocompromised, elderly, pregnant, or neonatal patients. The invertebrate model, Galleria mellonella, has emerged as an effective tool to study GBS-host interactions; specifically, those conserved within the innate arm of the immune system. We sought to determine the role of metal homeostasis functions in GBS infections of G. mellonella larvae and to validate this model as a tool to study GBS-host interactions. Our results indicate that wild-type GBS infects G. mellonella in a dose-dependent manner, replicates in the invertebrate host, induces larval melanization and larval killing. These results were significantly abrogated in cohorts of larvae infected with the isogenic cadD deletion mutant. Additionally, complementation restored GBS-dependent infection, bacterial burden, larval melanization, and killing to wild-type levels. Together, these results indicate that the G. mellonella model is a useful tool for studying GBS pathogenesis.

Distinct Agents Induce Streptococcus mutans Cells with Altered Biofilm Formation Capacity

Dental caries is a multifactorial biofilm- and sugar-dependent disease. This study investigated the influence of different agents on the induction of surviving Streptococcus mutans cells after successive treatment cycles and characterized the biofilms formed by these cells recovered posttreatment. The agents (with their main targets listed in parentheses) were compound 1771 (lipoteichoic acids), 4′ hydroxychalcone (exopolysaccharides), myricetin (exopolysaccharides), tt-farnesol (cytoplasmatic membrane), sodium fluoride (enolase—glycolysis), chlorhexidine (antimicrobial), and vehicle. Recovered cells from biofilms were generated from exposure to each agent during 10 cycles of consecutive treatments (modeled on a polystyrene plate bottom). The recovered cell counting was different for each agent. The recovered cells from each group were grown as biofilms on saliva-coated hydroxyapatite discs (culture medium with sucrose/starch). In S. mutans biofilms formed by cells recovered from biofilms previously exposed to compound 1771, 4′ hydroxychalcone, or myricetin, cells presented higher expression of the 16S rRNA, gyrA (DNA replication and transcription), gtfB (insoluble exopolysaccharides), and eno (enolase—glycolysis) genes and lower quantities of insoluble dry weight and insoluble exopolysaccharides than those derived from other agents. These findings were confirmed by the smaller biovolume of bacteria and/or exopolysaccharides and the biofilm distribution (coverage area). Moreover, preexposure to chlorhexidine increased exopolysaccharide production. Therefore, agents with different targets induce cells with distinct biofilm formation capacities, which is critical for developing formulations for biofilm control.

IMPORTANCE This article addresses the effect of distinct agents with distinct targets in the bacterial cell (cytoplasmatic membrane and glycolysis), the cell’s extracellular synthesis of exopolysaccharides that are important for cariogenic extracellular matrix construction and biofilm buildup in the generation of cells that persisted after treatment, and how these cells form biofilms in vitro. For example, if preexposure to an agent augments the production of virulence determinants, such as exopolysaccharides, its clinical value may be inadequate. Modification of biofilm formation capacity after exposure to agents is critical for the development of formulations for biofilm control to prevent caries, a ubiquitous disease associated with biofilm and diet.

Phytochemical Profile of Antibacterial Agents from Red Betel Leaf (Piper crocatum Ruiz and Pav) against Bacteria in Dental Caries

Based on data from The Global Burden of Disease Study in 2016, dental and oral health problems, especially dental caries, are a disease experienced by almost half of the world’s population (3.58 billion people). One of the main causes of dental caries is the pathogenesis of Streptococcus mutans. Prevention can be achieved by controlling S. mutans using an antibacterial agent. The most commonly used antibacterial for the treatment of dental caries is chlorhexidine. However, long-term use of chlorhexidine has been reported to cause resistance and some side effects. Therefore, the discovery of a natural antibacterial agent is an urgent need. A natural antibacterial agent that can be used are herbal medicines derived from medicinal plants. Piper crocatum Ruiz and Pav has the potential to be used as a natural antibacterial agent for treating dental and oral health problems. Several studies reported that the leaves of P. crocatum Ruiz and Pav contain secondary metabolites such as essential oils, flavonoids, alkaloids, terpenoids, tannins, and phenolic compounds that are active against S. mutans. This review summarizes some information about P. crocatum Ruiz and Pav, various isolation methods, bioactivity, S. mutans bacteria that cause dental caries, biofilm formation mechanism, antibacterial properties, and the antibacterial mechanism of secondary metabolites in P. crocatum Ruiz and Pav.

Understanding the Matrix: The Role of Extracellular DNA in Oral Biofilms

Dental plaque is the key etiological agent in caries formation and the development of the prevalent chronic oral inflammatory disease, periodontitis. The dental plaque biofilm comprises a diverse range of microbial species encased within a rich extracellular matrix, of which extracellular DNA (eDNA) has been identified as an important component. The molecular mechanisms of eDNA release and the structure of eDNA have yet to be fully characterized. Nonetheless, key functions that have been proposed for eDNA include maintaining biofilm structural integrity, initiating adhesion to dental surfaces, acting as a nutrient source, and facilitating horizontal gene transfer. Thus, eDNA is a potential therapeutic target for the management of oral disease–associated biofilm. This review aims to summarize advances in the understanding of the mechanisms of eDNA release from oral microorganisms and in the methods of eDNA detection and quantification within oral biofilms.

Compounds with Distinct Targets Present Diverse Antimicrobial and Antibiofilm Efficacy against Candida albicans and Streptococcus mutans, and Combinations of Compounds Potentiate Their Effect

Candida albicans and Streptococcus mutans interact synergistically in biofilms associated with a severe form of dental caries. Their synergism is driven by dietary sucrose. Thus, it is necessary to devise strategies to hinder the development of those biofilms and prevent cavities. Six compounds [tt-farnesol (sesquiterpene alcohol that decreases the bacterium acidogenicity and aciduricity and a quorum sensing fungal molecule), myricetin (flavonoid that interferes with S. mutans exopolysaccharides production), two 2'-hydroxychalcones and 4'-hydroxychalcone (intermediate metabolites for flavonoids), compound 1771 (inhibitor of lipoteichoic synthase in Gram-positive bacteria)] with targets in both fungus and bacterium and their products were investigated for their antimicrobial and antibiofilm activities against single-species cultures. The compounds and concentrations effective on single-species biofilms were tested alone and combined with or without fluoride to control initial and pre-formed dual-species biofilms. All the selected treatments eliminated both species on initial biofilms. In contrast, some combinations eliminated the bacterium and others the fungus in pre-formed biofilms. The combinations 4'-hydroxychalcone+tt-farnesol+myricetin, 4'-hydroxychalcone+tt-farnesol+fluoride, and all compounds together with fluoride were effective against both species in pre-formed biofilms. Therefore, combinations of compounds with distinct targets can prevent C. albicans and S. mutans dual-species biofilm build-up in vitro.

Modulation of Lipoteichoic Acids and Exopolysaccharides Prevents Streptococcus mutans Biofilm Accumulation

Dental caries is a diet–biofilm-dependent disease. Streptococcus mutans contributes to cariogenic biofilms by producing an extracellular matrix rich in exopolysaccharides and acids. The study aimed to determine the effect of topical treatments with compound 1771 (modulates lipoteichoic acid (LTA) metabolism) and myricetin (affects the synthesis of exopolysaccharides) on S. mutans biofilms. In vitro S. mutans UA159 biofilms were grown on saliva-coated hydroxyapatite discs, alternating 0.1% sucrose and 0.5% sucrose plus 1% starch. Twice-daily topical treatments were performed with both agents alone and combined with and without fluoride: compound 1771 (2.6 µg/mL), myricetin (500 µg/mL), 1771 + myricetin, fluoride (250 ppm), 1771 + fluoride, myricetin + fluoride, 1771 + myricetin + fluoride, and vehicle. Biofilms were evaluated via microbiological, biochemical, imaging, and gene expression methods. Compound 1771 alone yielded less viable counts, biomass, exopolysaccharides, and extracellular LTA. Moreover, the combination 1771 + myricetin + fluoride decreased three logs of bacterium counts, 60% biomass, >74% exopolysaccharides, and 20% LTA. The effect of treatments on extracellular DNA was not pronounced. The combination strategy affected the size of microcolonies and exopolysaccharides distribution and inhibited the expression of genes linked to insoluble exopolysaccharides synthesis. Therefore, compound 1771 prevented the accumulation of S. mutans biofilm; however, the effect was more pronounced when it was associated with fluoride and myricetin.

iTRAQ-based quantitative analysis reveals the mechanism underlying the changes in physiological activity in a glutamate racemase mutant strain of Streptococcus mutans UA159

Streptococcus mutans UA159 is responsible for human dental caries with robust cariogenic potential. Our previous study noted that a glutamate racemase (MurI) mutant strain (designated S. mutans FW1718), with the hereditary background of UA159, displayed alterations of morphogenesis, attenuated stress tolerance, and weakened biofilm-forming capabilities, accompanying with unclear mechanisms. In this study, we applied isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics to characterize the proteome profiles of the murI mutant strain vs. the wild-type strain in chemically defined media to elucidate the mechanisms by which S. mutans copes with MurI deficiency. Whole-cell proteins of S. mutans FW1718 and UA159 were assessed by iTRAQ-coupled LC-ESI-MS/MS. Furthermore, differentially expressed proteins (DEPs) were identified by Mascot, Gene Ontology (GO) annotation, Cluster of Orthologous Groups of proteins (COG), and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses. Finally, a protein-protein interaction (PPI) network was established using the Search Tool for the Retrieval of Interacting Genes/Proteins (STRING). Among 1173 total bacterial proteins identified, 112 DEPs exhibited altered expression patterns in S. mutans UA159 with or without the murI mutation. The ΔmurI cells displayed an increase in the relative expression of 93 proteins (fold change ≥ 1.2, p < 0.05) and a decrease in 29 proteins (fold change ≤ 0.833, p < 0.05) compared with the wild-type cells. PPI analysis revealed a complex network of DEPs containing 191 edges and 122 nodes. The DEPs significantly upregulated after murI knockout had roles in diverse functional processes spanning cell-wall biosynthesis, energy production, and DNA replication and repair. We identified distinct variations and diverse modulators caused by murI mutation in the proteome of S. mutans, indicating that the modification of cell membrane structure, redistribution of energy metabolism and enhanced nucleic acid machinery contributed to the S. mutans response to specific environmental contexts.