Identification of anti-biofilm components in Withania somnifera and their effect on virulence of Streptococcus mutans biofilms

Trichoderma-derived emodin competes with ExpR and ExpI of Pectobacterium carotovorum subsp. carotovorum to biocontrol bacterial soft rot

BACKGROUND

Quorum sensing inhibitors (QSIs) are an emerging control tool that inhibits the quorum sensing (QS) system of pathogenic bacteria. We aimed to screen for potential QSIs in the metabolites of Trichoderma and to explore their inhibitory mechanisms.

RESULTS

We screened a strain of Trichoderma asperellum LN004, which demonstrated the ability to inhibit the color development of Chromobacterium subtsugae CV026, primarily attributed to the presence of emodin as its key QSI component. The quantitative polymerase chain reaction with reverse transcription results showed that after emodin treatment of Pectobacterium carotovorum subsp. carotovorum (Pcc), plant cell wall degrading enzyme-related synthetic genes were significantly downregulated, and the exogenous enzyme synthesis gene negative regulator (rsmA) was upregulated 3.5-fold. Docking simulations indicated that emodin could be a potential ligand for ExpI and ExpR proteins because it exhibited stronger competition than the natural ligands in Pcc. In addition, western blotting showed that emodin attenuated the degradation of n-acylhomoserine lactone on the ExpR protein and protected it. Different concentrations of emodin reduced the activity of pectinase, cellulase, and protease in Pcc by 20.81%-72.21%, 8.38%-52.73%, and 3.57%-47.50%. Lesion size in Chinese cabbages, carrots and cherry tomatoes following Pcc infestation was reduced by 10.02%-68.57%, 40.17%-88.56% and 11.36%-86.17%.

CONCLUSION

Emodin from T. asperellum LN004 as a QSI can compete to bind both ExpI and ExpR proteins, interfering with the QS of Pcc and reducing the production of virulence factors. The first molecular mechanism reveals the ability of emodin as a QSI to competitively inhibit two QS proteins simultaneously. © 2023 Society of Chemical Industry.

In silico analysis unravels the promising anticariogenic efficacy of fatty acids against dental caries causing Streptococcus mutans

Globally, dental caries is a prevalent oral disease caused by cariogenic bacteria, primarily Streptococcus mutans. It establishes caries either through sucrose-dependent (via glycosyltransferases) or through sucrose-independent (via surface adhesins Antigen I/II) mechanism. Sortase A (srtA) attaches virulence-associated adhesins to host tissues. Because of their importance in the formation of caries, targeting these proteins is decisive in the development of new anticariogenic drugs. High-throughput virtual screening with LIPID MAPS -a fatty acid database was performed. The selected protein-ligand complexes were subjected to molecular dynamics simulation (MDs). The Binding Free Energy of complexes was predicted using MM/PBSA. Further, the drug-likeness and pharmacokinetic properties of ligands were also analyzed. Out of 46,200 FAs scrutinized virtually against the three protein targets (viz., GtfC, Ag I/II and srtA), top 5 FAs for each protein were identified as the best hit based on interaction energies viz., hydrogen bond numbers and hydrophobic interaction. Further, two common FAs (LMFA01050418 and LMFA01040045) that showed high binding affinity against Ag I/II and srtA were selected for MDs analysis. A 100ns MDs unveiled a stable conformation. Results of Rg signified that FAs does not induce significant structural & conformational changes. SASA indicated that the complexes maintain higher thermodynamic stability during MDs. The predicted binding free energy (MM/PBSA) of complexes elucidated their stable binding interaction. ADME analysis suggested the FAs are biologically feasible as therapeutic candidates. Overall, the presented in silico data is the first of its kind in delineating FAs as promising anticaries agents of future.Communicated by Ramaswamy H. Sarma.

Novel Lactotransferrin-Derived Antimicrobial Peptide LF-1 Inhibits the Cariogenic Virulence Factors of Streptococcus mutans

We previously developed a novel lactotransferrin-derived antimicrobial peptide, LF-1, with selective antibacterial activity against the characteristic cariogenic bacterium Streptococcus mutans. This study further investigated the effects of LF-1 on the cariogenic virulence factors of S. mutans and evaluated the changes in virulence-associated enzymes and genes; the viability, acidogenicity, and aciduricity of planktonic S. mutans; and initial colonisation and biofilm formation after treatment with LF-1. The method of qRT-PCR was used to evaluate S. mutans virulence-associated gene expression. LF-1 interfered with the cell viability of S. mutans within 6 h. LF-1 inhibited the acidogenicity and aciduricity of S. mutans, with reduced lactic acid production and survival in a lethal acidic environment, and inactivated lactate dehydrogenase and F1F0-ATPase activity. LF-1 decreased surface-adherent S. mutans within 60 min and inhibited S. mutans biofilm formation, where scanning electron microscopy and confocal laser scanning microscopy showed reduced extracellular matrix and bacteria. LF-1 downregulates S. mutans virulence-associated gene expression. LF-1 inhibited the growth and cariogenic virulence factors of S. mutans in vitro with a reduction in key enzymatic activity and downregulation of virulence-associated gene expression. LF-1 has promising application prospects in the fight against S. mutans and dental caries.

Effects of cigarette smoking on the growth of Streptococcus mutans biofilms: An in vitro study

The increased incidence of dental caries by cigarette smoking (CS) has been widely reported in epidemiological studies, but the relationship between CS and cariogenic biofilm growth has been rarely studied. This study aims to investigate the effects of CS exposure on the growth and virulence of Streptococcus mutans biofilms (S. mutans). Briefly, S. mutans biofilms were formed on saliva-coated hydroxyapatite disks, which were exposed to CS 1, 3, and 6 times per day, respectively. In addition, S. mutans biofilms without CS exposure were considered as the control group. Acidogenicity, dry weight, colony-forming units (CFUs), water-soluble/insoluble extracellular polysaccharides (EPSs), and intracellular polysaccharides (IPSs) were analyzed and confocal laser scanning microscopy (CLSM) images of 74-h-old S. mutans biofilms were obtained. The lowest accumulation of biofilms and EPSs were detected in the 6 times/day CS exposure group compared with those of the control group and other CS exposure groups in 74-h-old S. mutans biofilms. CLSM also revealed the lowest bacterial count (live and dead cells) and EPSs biovolume in the six times/day CS exposure group in 74-h-old S. mutans biofilms. CS exposure inhibited the growth of S. mutans biofilm in vitro study, the anti-cariogenic biofilm formation was enhanced with a dose (frequency)-dependent at which frequency has more influence in the present findings.

Relationship between sucrose concentration and bacteria proportion in a multispecies biofilm: : Sucrose challenges to a multispecies biofilm

Objective: The aim of this study was to evaluate the relationship between sucrose concentration and bacteria proportion in a multispecies biofilm model. Methods: Streptococcus mutans (S. mutans), Streptococcus oralis (S. oralis), and Actinomyces naeslundii (A. naeslundii) were chose to form a multispecies biofilm. Different concentration (0-40%) of sucrose was introduced to the multispecies biofilm 3 times per day (30 min per time). And then the bacteria proportion and acid production of the biofilms were analyzed. Results: Increasing sucrose level increased CFU count of S. mutans up to a certain concentration (5% sucrose), after which the number of S. mutans slightly decreased, but the CFU counts of S. oralis and A. naeslundii continually decreased with sucrose concentration increase, especially, from 5% sucrose, the reduction was significant, and S. mutans became the dominant species in the biofilms. Furthermore, the acid production ability of the multispecies biofilm gradually increased and slightly decreased with sucrose concentration increased, and the turning concentration was 5%. Conclusion: Our findings suggest that increasing sucrose level could increase the competitiveness of S. mutans in the multispecies biofilm, which may shift the biofilm to a more cariogenic one, and 5% sucrose formed a most cariogenic biofilm in this study.

Can Leaves and Stems of Rubus idaeus L. Handle Candida albicans Biofilms?

Candida albicans is an opportunistic pathogen involved in many infections, especially linked to implanted medical devices. Its ability to form biofilms complicates the treatment of these infections as few molecules are active against sessile C. albicans. The aim of this study was to evaluate the potential of leaves, three-month-old and one-year-old stems of Rubus idaeus L. against C. albicans biofilm growth. Extractions with a polarity gradient were carried out on hydroacetonic extracts and followed by fractionation steps. The obtained extracts and fractions were tested for their anti-biofilm growth activity against C. albicans using XTT method. Compounds of active subfractions were identified by LC-MS. The hexane extracts from leaves and stems were the most active against the fungus with IC50 at 500 and 250 µg/mL. Their bioguided fractionation led to 4 subfractions with IC50 between 62.5 and 125 µg/mL. Most of the components identified in active subfractions were fatty acids and terpenoïds.

Global proteomic analysis deciphers the mechanism of action of plant derived oleic acid against Candida albicans virulence and biofilm formation

Candida albicans is a commensal fungus in humans, mostly found on the mucosal surfaces of the mouth, gut, vagina and skin. Incidence of ever increasing invasive candidiasis in immunocompromised patients, alarming occurrence of antifungal resistance and insufficient diagnostic methods demand more focused research into C. albicans pathogenicity. Consequently, in the present study, oleic acid from Murraya koenigii was shown to have the efficacy to inhibit biofilm formation and virulence of Candida spp. Results of in vitro virulence assays and gene expression analysis, impelled to study the protein targets which are involved in the molecular pathways of C. albicans pathogenicity. Proteomic studies of differentially expressed proteins reveals that oleic acid induces oxidative stress responses and mainly targets the proteins involved in glucose metabolism, ergosterol biosynthesis, lipase production, iron homeostasis and amino acid biosynthesis. The current study emphasizes anti-virulent potential of oleic acid which can be used as a therapeutic agent to treat Candida infections.

Quorum sensing inhibitory activity of the metabolome from endophytic Kwoniella sp. PY016: characterization and hybrid model-based optimization

Quorum sensing, the microbial communication system, is gaining importance as a therapeutic target against pathogens. The two key reasons for the rising demand of quorum sensing (QS) inhibitory molecules are low selective pressure to develop resistance by pathogens and possibility of more species-specific effects. Due to complex interactions in a unique niche of live plant tissues, endophytes, as a survival mechanism, potentially produce various bioactive compounds such as QS inhibitors. We report the isolation of an endophytic fungus Kwoniella sp. PY016 from the medicinal plant "Bahera" (Terminalia bellirica), which exhibits substantial quorum sensing inhibition and anti-biofilm activities against the standard test organism, Chromobacterium violaceum. Sugar, sugar alcohol, carboxylic acid, lipid, and phenolic classes of metabolites (predominantly xylitol) are responsible components of the metabolome for the desired bioactivity. A judicious combination of single-factor-at-a-time strategy and artificial neural network modeling combined with genetic algorithm was employed for the selection and optimization of the critical process and medium parameters. Through this newly adopted hybrid model-based optimization, the quorum sensing inhibitory activity of the endophytic metabolome was increased by ~ 30%. This is the first report on optimization of QS inhibitory activity from any fungal endophyte using such a hybrid advanced approach.

Difference in virulence and composition of a cariogenic biofilm according to substratum direction

The aim of this study was to investigate the difference in composition and virulence of Streptococcus mutans biofilms according to substratum direction. S. mutans biofilms (46-h-old) were formed on three different saliva-coated hydroxyapatite (sHA) disc direction groups: downward (discs placed in the direction of gravity), vertical (discs placed parallel to gravity direction), and upward (discs placed opposite to gravity). The 46-h-old biofilms on sHA discs in the upward direction showed the highest biofilm accumulation, colony forming unit (CFU) count, and extracellular polysaccharide (EPS) amount, followed by those in the vertical and downward directions. In the confocal laser scanning microscopy (CLSM) study, the biofilms in the upward direction also showed the highest bacterial count (live or dead cells) and EPS biovolume. Scanning electron microscopy (SEM) analysis confirmed the microbiological and biochemical results. In addition, biofilm density and acid production were higher in the upward direction than those in the other directions. Our findings suggest that substratum direction, which might be related to gravity, strongly influences the formation and virulence of cariogenic biofilms and subsequent initiation of dental caries. Collectively, the differences in the formation and virulence of cariogenic biofilms are related to the direction of tooth surface (occlusal surfaces of mandibular teeth > proximal surfaces > occlusal surfaces of maxillary teeth).

Effect of Bacoside A on growth and biofilm formation by Staphylococcus aureus and Pseudomonas aeruginosa

The goal of this study was to evaluate the antibiofilm and antimicrobial activities of Bacoside A, a formulation of phytochemicals from Bacopa monnieri, against Staphylococcus aureus and Pseudomonas aeruginosa, which are known to form biofilms as one of their virulence traits. The antimicrobial effects of Bacoside A were tested using the minimum inhibitory concentration and minimum bactericidal concentration assays. A cell membrane disruption assay was performed to find its possible target site. MTT assay, crystal violet assay, and microscopic studies were performed to assess the antibiofilm activity. Bacoside A showed antimicrobial activity against both test organisms in their planktonic and biofilm states. At a subminimum inhibitory concentration of 200 μg·mL^-1, Bacoside A significantly removed ∼88%-93% of bacterial biofilm developed on microtiter plates. Biochemical and microscopic studies suggested that the eradication of biofilm might be due to the loss of extracellular polymeric substances and to a change in cell membrane integrity of the selected bacterial strains treated with Bacoside A. These results indicate that Bacoside A might be considered as an antimicrobial having the ability to disrupt biofilms. Thus, either alone or in combination with other therapeutics, Bacoside A could be useful to treat biofilm-related infections caused by opportunistic bacterial pathogens.

Plant Natural Products Targeting Bacterial Virulence Factors

Decreased antimicrobial efficiency has become a global public health issue. The paucity of new antibacterial drugs is evident, and the arsenal against infectious diseases needs to be improved urgently. The selection of plants as a source of prototype compounds is appropriate, since plant species naturally produce a wide range of secondary metabolites that act as a chemical line of defense against microorganisms in the environment. Although traditional approaches to combat microbial infections remain effective, targeting microbial virulence rather than survival seems to be an exciting strategy, since the modulation of virulence factors might lead to a milder evolutionary pressure for the development of resistance. Additionally, anti-infective chemotherapies may be successfully achieved by combining antivirulence and conventional antimicrobials, extending the lifespan of these drugs. This review presents an updated discussion of natural compounds isolated from plants with chemically characterized structures and activity against the major bacterial virulence factors: quorum sensing, bacterial biofilms, bacterial motility, bacterial toxins, bacterial pigments, bacterial enzymes, and bacterial surfactants. Moreover, a critical analysis of the most promising virulence factors is presented, highlighting their potential as targets to attenuate bacterial virulence. The ongoing progress in the field of antivirulence therapy may therefore help to translate this promising concept into real intervention strategies in clinical areas.

Functional Relationship between Sucrose and a Cariogenic Biofilm Formation

Sucrose is an important dietary factor in cariogenic biofilm formation and subsequent initiation of dental caries. This study investigated the functional relationships between sucrose concentration and Streptococcus mutans adherence and biofilm formation. Changes in morphological characteristics of the biofilms with increasing sucrose concentration were also evaluated. S. mutans biofilms were formed on saliva-coated hydroxyapatite discs in culture medium containing 0, 0.05, 0.1, 0.5, 1, 2, 5, 10, 20, or 40% (w/v) sucrose. The adherence (in 4-hour biofilms) and biofilm composition (in 46-hour biofilms) of the biofilms were analyzed using microbiological, biochemical, laser scanning confocal fluorescence microscopic, and scanning electron microscopic methods. To determine the relationships, 2nd order polynomial curve fitting was performed. In this study, the influence of sucrose on bacterial adhesion, biofilm composition (dry weight, bacterial counts, and water-insoluble extracellular polysaccharide (EPS) content), and acidogenicity followed a 2nd order polynomial curve with concentration dependence, and the maximum effective concentrations (MECs) of sucrose ranged from 0.45 to 2.4%. The bacterial and EPS bio-volume and thickness in the biofilms also gradually increased and then decreased as sucrose concentration increased. Furthermore, the size and shape of the micro-colonies of the biofilms depended on the sucrose concentration. Around the MECs, the micro-colonies were bigger and more homogeneous than those at 0 and 40%, and were surrounded by enough EPSs to support their structure. These results suggest that the relationship between sucrose concentration and cariogenic biofilm formation in the oral cavity could be described by a functional relationship.