Biological potential, chemical profiling, and molecular docking study of Morus alba L. extracts

Morus alba L. is a plant with a long history of dietary and medicinal uses. We hypothesized that M. alba possesses a significant biological potential. In that sense, we aimed to generate the chemical, antimicrobial, toxicological, and molecular profile of M. alba leaf and fruit extracts. Our results showed that extracts were rich in vitamin C, phenols, and flavonoids, with quercetin and pterostilbene concentrated in the leaf, while fisetin, hesperidin, resveratrol, and luteolin were detected in fruit. Extracts exhibited antimicrobial activity against all tested bacteria, including multidrug-resistant strains. The widest inhibition zones were in Staphylococcus aureus ATCC 33591. The values of the minimum inhibitory concentration ranged from 15.62 μg/ml in Enterococcus faecalis to 500 μg/ml in several bacteria. Minimum bactericidal concentration ranged from 31.25 μg/ml to 1000 μg/ml. Extracts impacted the biofilm formation in a concentration-dependent and species-specific manner. A significant difference in the frequency of nucleoplasmic bridges between the methanolic extract of fruit (0.5 μg/ml, 1 μg/ml, 2 μg/ml), as well as for the frequency of micronuclei between ethanolic extract of leaf (2 μg/ml) and the control group was observed. Molecular docking suggested that hesperidin possesses the highest binding affinity for multidrug efflux transporter AcrB and acyl-PBP2a from MRSA, as well as for the SARS-CoV-2 Mpro. This study, by complementing previous research in this field, gives new insights that could be of great value in obtaining a more comprehensive picture of the Morus alba L. bioactive potential, chemical composition, antimicrobial and toxicological features, as well as molecular profile.

Inhibitory effect of Lonicera japonica flos on Streptococcus mutans biofilm and mechanism exploration through metabolomic and transcriptomic analyses

Introduction

Streptococcus mutans was the primary pathogenic organism responsible for dental caries. Lonicera japonica flos (LJF) is a traditional herb in Asia and Europe and consumed as a tea beverage for thousands of years.

Methods

The inhibitory effect and mechanism of LJF on biofilm formation by S. mutans was investigated. The active extracts of LJF were validated for their inhibitory activity by examining changes in surface properties such as adherence, hydrophobicity, auto-aggregation abilities, and exopolysaccharides (EPS) production, including water-soluble glucan and water-insoluble glucan.

Results and discussion

LJF primarily inhibited biofilm formation through the reduction of EPS production, resulting in alterations in cell surface characteristics and growth retardation in biofilm formation cycles. Integrated transcriptomic and untargeted metabolomics analyses revealed that EPS production was modulated through two-component systems (TCS), quorum sensing (QS), and phosphotransferase system (PTS) pathways under LJF stress conditions. The sensing histidine kinase VicK was identified as an important target protein, as LJF caused its dysregulated expression and blocked the sensing of autoinducer II (AI-2). This led to the inhibition of response regulator transcriptional factors, down-regulated glycosyltransferase (Gtf) activity, and decreased production of water-insoluble glucans (WIG) and water-soluble glucans (WSG). This is the first exploration of the inhibitory effect and mechanism of LJF on S. mutans, providing a theoretical basis for the application of LJF in functional food, oral health care, and related areas.

4-hydroxy-3-methoxybenzaldehyde causes attrition of biofilm formation and quorum sensing-associated virulence factors of Streptococcus mutans

OBJECTIVE

The present study investigated the effects of 4-hydroxy-3-methoxybenzaldehyde (4-H-3-MB) against Streptococcus mutans (S. mutans) using an in vitro cariogenic biofilm model.

DESIGN

The antimicrobial susceptibility of biofilm-forming S. mutans was evaluated by disc diffusion method. In vitro investigations were performed using crystal violet staining assay (biofilm assay), exopolysaccharide (EPS) assay, acid production, growth curve analysis, optical microscopic, and FE-SEM analyses to determine the antibiofilm activity of 4-H-3-MB.

RESULTS

S. mutans (SDC-05) was resistant to ampicillin, piperacillin/tazobactam and ceftriaxone, whereas the other strains of S. mutans (SDC-01, 02, 03 and SDC-04) were sensitive to all the antibiotics tested. 4-H-3-MB showed promising antibiofilm activity on S. mutans UA159 (79.81 %, 67.76 % and 56.31 %) and S. mutans SDC-05 (77.00 %, 59.48 % and 48.22 %) at the lowest concentration of 0.2, 0.1, 0.05 mg/ml. 4-H-3-MB did not inhibit bacterial growth even at concentrations 0.2 mg/ml. Similarly, 4-H-3-MB led to significant attrition in exopolysaccharide (EPS) and acid production by S. mutans UA159 and S. mutans (SDC-05) at the concentration of 0.2, 0.1 mg/ml, respectively. Optical microscopy and FE-SEM analysis 4-H-3-MB reduced the biofilm thickness of S. mutans UA159 and S. mutans SDC-05 relative to the untreated specimens.

CONCLUSION

4-H-3-MB significantly inhibited biofilm formation by S. mutans in a dose-dependent manner. Hence, our findings indicate that the active principle of 4-H-3-MB could be used as a biofilm inhibiting agent against S. mutans.

Characterization of Leuconostoc mesenteroides MJM60376 as an oral probiotic and its antibiofilm activity

Lactic acid bacteria have been widely used as probiotics for improving gut health. However, studies on oral probiotics were very limited. In this study, 67 lactic acid bacteria (LAB) were isolated from fermented food and screened for antagonistic activity against Streptococcus mutans, the causative pathogen of dental caries. Leuconostoc mesenteroides MJM60376 showed the highest antagonistic activity against S. mutans KCTC3065. L. mesenteroides MJM60376 also showed oral probiotic characteristics including weak acid production, lysozyme tolerance, adhesion to oral epithelial cell (YD-38), antibiotic susceptibility, and good coaggregation ability with S. mutans. Furthermore, the biofilm formation of S. mutans was significantly reduced when cocultured with L. mesenteroides. Scanning electron microscopy analysis showed that amounts of attached bacteria of S. mutans and network-like structures were significantly reduced by L. mesenteroides MJM60376. Cell-free supernatant (CFS) of L. mesenteroides MJM60376 also greatly inhibited biofilm formation of S. mutans from the adherent stage, the activity remained even after it was treated with catalase, trypsin, or pH neutralized. Expression levels of biofilm formation-related genes were significantly reduced in S. mutans when it was treated with the CFS of L. mesenteroides MJM60376. Therefore, L. mesenteroides MJM60376 has great potential to be used as a multifunctional ingredient.

Morus alba: a comprehensive phytochemical and pharmacological review

Morus alba is a fast-growing shrub or medium-sized tree with a straight, cylindrical trunk. Medicinally, whole plants, leaves, fruits, branches, and roots have been employed. Google Scholar, PubMed, Scopus, and Web of Science were used to search for relevant material on the phytochemical components and pharmacologic and mechanism of action of the Morus alba. This was reviewed to assess important updates about Morus alba. The fruits of Morus alba have traditionally been used as an analgesic, anthelmintic, antibacterial, anti-rheumatic, diuretic, hypotensive, hypoglycemia, purgative, restorative, sedative tonic, and blood stimulant. Various plant parts were used as a cooling, sedating, diuretic, tonic, and astringent agent to treat nerve disorders. The plant contained tannins, steroids, phytosterols, sitosterol, glycosides, alkaloids, carbohydrates, proteins, and amino acids, as well as saponins, triterpenes, phenolics, flavonoids, benzofuran derivatives, anthocyanins, anthraquinones, glycosides, vitamins, and minerals. Previous pharmacological research identified antimicrobial, anti-inflammatory, immunological, analgesic, antipyretic, antioxidant, anti-cancer, antidiabetic, gastrointestinal, respiratory, cardiovascular, hypolipidemic, anti-obesity, dermatological, neurological, muscular, and protecting effects. This study looked at Morus alba's traditional uses, chemical components, and pharmacological effects.

Potential oral probiotic Lactobacillus pentosus MJM60383 inhibits Streptococcus mutans biofilm formation by inhibiting sucrose decomposition

Streptococcus mutans is known as a contributor to dental caries. In this work, Lactobacillus pentosus MJM60383 was selected for its strong antagonistic activity against S. mutans and was characterized by good oral probiotic properties including lysozyme tolerance, adhesive ability to oral cells, good aggregation (auto-aggregation, co-aggregation) ability, hydrogen peroxide production and inhibition of biofilm formation of S. mutans. L. pentosus MJM60383 also exhibited safety as a probiotic characterized by no hemolytic activity, no D-lactate production, no biogenic amine production, and susceptibility to antibiotics. Furthermore, the biofilm formation of S. mutans was also significantly inhibited by the supernatant of L. pentosus MJM60383. An anti-biofilm mechanism study revealed that sucrose decomposition and the production of water-insoluble exopolysaccharides by S. mutans were inhibited by the treatment with L. pentosus MJM60383 supernatant. Real-time PCR analysis indicated that the supernatant of L. pentosus MJM60383 significantly inhibited the mRNA expression of S. mutans glycosyltransferases, which synthesize glucan to construct biofilm architecture and mediate bacterial adherence. Our study demonstrated L. pentosus MJM60383 as a potential oral probiotic and revealed its anti-biofilm mechanism.

Discovery of Novel Iminosugar Compounds Produced by Lactobacillus paragasseri MJM60645 and Their Anti-Biofilm Activity against Streptococcus mutans

The oral cavity contains a number of microbes. They interact with each other and play an important role in human health. Among oral cariogenic microbes, Streptococcus mutans is recognized a major etiological bacteria of dental caries. Lactobacilli strains have been promoted as possible probiotic agents against S. mutans. However, their inhibitory mechanism has not been well elucidated yet. In the present study, two new compounds with strong antibiofilm activities were purified from the culture supernatant of Lactobacillus paragasseri MJM60645, which was isolated from the human oral cavity. These compounds showed strong inhibitory activities against S. mutans biofilm formation, with IC50 (concentration at which 50% biofilm was inhibited) of 30.4 μM for compound 1 and 18.9 μM for compound 2. However, these compounds did not show bactericidal activities against S. mutans. Structure elucidation by nuclear magnetic resonance (NMR) and mass spectrometry showed that compound 1 was composed of two arabinofuranose iminosugars jointed with one glycerol and oleic acid, and compound 2 was composed of two arabinofuranose iminosugars jointed with one glycerol and nervonic acid. To the best of our knowledge, these structures were discovered for the first time in this study. Treatment of S. mutans with compound 1 strongly downregulated expression levels of genes related to biofilm formation, including gtfB, gtfC, gtfD, gbpB, brpA, spaP, ftf, and smu0630 without affecting the expression of comDE or relA. This study provides new insights into novel molecules produced by Lactobacillus to regulate the pathogenesis of S. mutans, facilitating a better understanding of the mechanism for interactions between Lactobacillus and S. mutans. IMPORTANCE In this study, we isolated lactic acid bacteria that inhibit streptococcal biofilm from the oral cavity of infants and identified two novel compounds from the supernatant of their culture broth. The two compounds are structurally similar, and both consist of iminosugars, glycerol, and unsaturated fatty acid. A search of the SciFinder database revealed that these structures are novel and were discovered for the first time in this study. Mechanism studies have shown that these compounds can inhibit the expression of biofilm synthesis-related genes. This is the first report that lactic acid bacteria inhibit streptococcal biofilms by small molecules with new chemical structures. This study not only expands the understanding of natural products derived from lactic acid bacteria but also provides a new paradigm for the understanding of the interaction of bacteria in the oral microbiota.

Effects of free and nano encapsulated bovine lactoferrin on the viability and acid production by Streptococcus mutans biofilms

Tooth decay is one of the most common diseases that humans face during their lifetime. Streptococcus mutans is one of the most critical factors of early tooth decay. These bacteria may produce biofilms in the mouth, which are more resistant to antimicrobial agents. S. mutans may also demineralize tooth enamel by producing lactic acid. In this study, the effect of nanoliposomes containing lactoferrin at three different concentrations (1.5, 3, and 6 mg ml^-1 l) on the biofilm formed by S. mutans was investigated. Nanoliposomes were prepared using the thin-layer hydration method. An active attachment model (AAA) was used to evaluate biofilm and lactic acid production. The results showed that nano encapsulated lactoferrin could reduce CFU of biofilm more effectively than free lactoferrin. Lactoferrin-containing nanoliposomes also significantly reduced lactic acid production by S. mutans. Therefore, nano encapsulated lactoferrin may be used along with other dental caries control methods to increase anti caries efficacy.

PDIA, an Iminosugar Compound with a Wide Biofilm Inhibitory Spectrum Covering Both Gram-Positive and Gram-Negative Human Bacterial Pathogens

Many difficult-to-treat human infections related to catheters and other indwelling devices are caused by bacteria residing in biofilms. One of the key properties of microorganisms residing in a biofilm is decreased susceptibility towards antimicrobial agents. Therefore, many different approaches have been researched to destroy or inhibit biofilm production by bacteria. Different iminosugars (IS) were reported to inhibit biofilm formation in S. mutans, S. aureus, and P. aeruginosa. The aim of this study was to look for a spectrum of the activity in one of these IS. The iminosugar PDIA beta-1-C-propyl-1,4-dideoxy-1,4-imino-L-arabinitol was tested in vitro at the same concentration against 30 different strains of the most important Gram-negative and Gram-positive human pathogens looking for their biofilm production and viability at different time intervals. It appeared that PDIA inhibited biofilm production of Enterobacter spp., P. aeruginosa, Enterococcus spp. and S. aureus in 8 h, and Klebsiella spp., Acinetobacter spp. and S.epidermidis in 24 h. PDIA caused no growth inhibition of the tested bacteria at a concentration of 0.9 mM. Our results indicate a broad-spectrum biofilm inhibitory activity of PDIA. which may be the basis for future application studies that will help in control of the associated device and biofilm-related infections caused by a wide spectrum of the causative agents.

Anti-Inflammatory and Anti-Bacterial Potential of Mulberry Leaf Extract on Oral Microorganisms

Mulberry leaves extract (Morus alba extracts; MAE) is known to have therapeutic potentials for numerous human diseases, including diabetes, neurological disorders, cardiovascular diseases, and cancers. However, there has not been sufficient research proving therapeutic effects on oral disease and its related oral risk factors. Thus, we investigated whether MAE has any anti-inflammatory and anti-bacterial effects on risk factors causing oral infectious diseases. To examine the anti-inflammatory response and bacterial inhibition of MAE, we measured intracellular reactive oxygen species (ROS) generation, production of pro-inflammatory cytokines, and the bacterial growth rate. Our study showed that MAE has anti-inflammatory activities, which inhibit the ROS generation and suppressed the production of pro-inflammatory cytokines (TNF-α and IL-6) in human monocyte THP-1 cells by stimulating lipopolysaccharide (LPS) and/or F. nucleatum, which are the virulent factors in periodontal diseases. Furthermore, MAE inhibited the bacterial growth on oral microorganisms (F. nucleatum and S. mutans) infected THP-1 cells. These findings suggested that MAE could be a potential natural source for therapeutic drugs in oral infectious disease.

Phytochemistry, bioactivities and future prospects of mulberry leaves: A review

Mulberry leaves (MLs) have been used traditionally to raise silkworms and as herbs and herbal drinks. In vitro and in vivo studies as well as some clinical trials provide some evidence of health benefits, mostly for ML extracts. ML extracts showed antioxidant, hypoglycemic, anticholesterol (affecting lipid metabolism), antiobesity, anti-inflammatory, anticancer activities, and so on. These might be linked to strong antioxidant activities, inhibition of α-glucosidase and α-amylase, reduction of foam cell formation, inhibition of fat formation, decrease of NF-κB activity, and the promotion or induction of apoptosis. Phenolic constituents, especially flavonoids, phenolic acids and alkaloids, are likely to contribute to the reported effects. The phytochemistry and pharmacology of MLs confer the traditional and current uses as medicine, food, fodder, and cosmetics. This paper reviews the economic value, chemical composition and pharmacology of MLs to provide a reference for the development and utilization of MLs.

Pharmacological Activities for Morus alba L., Focusing on the Immunostimulatory Property from the Fruit Aqueous Extract

Depending on the extraction method, numerous compounds that have specific pharmacological effects can be obtained from M. alba L. There is a growing scientific interest in health problems related to aging. Efforts to develop safe immune-enhancing pharmaceuticals are increasing. This review aims to summarize and critically discuss the immunity enhancement effects and pharmaceutical efficacy of M. alba L. extracts. The scientific database search was conducted using Google Scholar, Web of Science, and PubMed until May 2021. Additional articles were identified and obtained from references in the retrieved articles. Ethanol or methanol extraction of various parts of M. alba L. identified a large amount of phenols and flavonoids, which are effective for immunosuppression, antioxidants, and cardiovascular diseases, and are antibacterial, and anticancer. Water extraction of M. alba L. enhanced the innate immune response based on immune cell activation. A polysaccharide and an alkaloid related to increased macrophage activity were isolated from M. alba L. fruit extracts. M. alba L. fruit water extracts primarily induced the production of pro-inflammatory substances, in model organisms, via TLR4 in immune cells. Water extracts have been shown to be effective in pathogen defense and tumor suppression by enhancing macrophage activity. Based on our literature review on the bioactivity of M. alba L. fruit extracts, particularly in relation to their immunity enhancement activity, we anticipate that M. alba-derived pharmaceuticals will have excellent potential in future medical research.

Comparative genomic analysis of azasugar biosynthesis

Azasugars are monosaccharide analogs in which the ring oxygen is replaced with a nitrogen atom. These well-known glycosidase inhibitors are of interest as therapeutics, yet several aspects of azasugars remain unknown including their distribution, structural diversity, and chemical ecology. The hallmark signature of bacterial azasugar biosynthesis is a three gene cluster (3GC) coding for aminotransferase, phosphatase, and dehydrogenase enzymes. Using the bioinformatics platform Enzyme Similarity Tool (EST), we identified hundreds of putative three gene clusters coding for azasugar production in microbial species. In the course of this work, we also report a consensus sequence for the aminotransferase involved in azasugar biosynthesis as being: SGNXFRXXXFPNXXXXXXXLXVPXPYCXRC. Most clusters are found in Bacillus and Streptomyces species which typically inhabit soil and the rhizosphere, but some clusters are found with diverse species representation such as Photorhabdus and Xenorhabdus which are symbiotic with entomopathogenic nematodes; the human skin commensal Cutibacterium acnes, and the marine Bacillus rugosus SPB7, a symbiont to the sea sponge Spongia officinalis. This pan-taxonomic survey of the azasugar 3GC signature may lead to the identification of new azasugar producers, facilitate studies of their natural functions, and lead to new potential therapeutics.

Phytochemical analysis of medicinal plants of Nepal and their antibacterial and antibiofilm activities against uropathogenic Escherichia coli

BACKGROUND

A biofilm is an extracellular polymeric substance (EPS) composed of polysaccharides, proteins, nucleic acids, and lipids that impede antibiotics and immune cells, thus providing a shielded environment for bacterial growth. Due to biofilm formation, some microbes can show up to 1000 fold increased resistance towards the antibiotics than the normal planktonic forms. The study was conducted to screen the crude extracts of medicinal plants used in Nepal for their in vitro antibiofilm activities.

METHODS

Total phenolic and total flavonoid contents were determined by using a Folin-Ciocalteau reagent and aluminium trichloride method, respectively. Resazurin assay was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). The initial antibiofilm activities and their inhibitory concentration (IC₅₀) values were determined by the microtiter based modified crystal violet staining method.

RESULTS

Out of 25 different plant extracts were used for the study, methanolic extracts of 20 plants showed a biofilm inhibition activity against five different strong biofilm producing Escherichia coli strains. Calotropis gigantea exhibited inhibition against all five different E. coli strains with IC₅₀ values ranging from 299.7 ± 20.5 to 427.4 ± 2.7 μg/mL. Apart from that, Eclipta prostrata also showed biofilm formation inhibition, followed by Eupatorium adenophorum, Moringa oleifera, Ocimum tenuifolium, Oxalis lantifolia, Prunus persica, and Urtica parviflora. The extracts of C. gigantea, E. prostrata, Mangifera indica, O. tenuifolium, P. persica, and U. parviflora exhibited a moderate to poor MIC value ranging from 625 to 2500 μg/mL. The highest amount of phenolic content (TPC) was found in Acacia catechu followed by Morus alba, which was 38.9 and 25.1 mg gallic acid equivalents, respectively. The highest amount of flavonoid content was found in A. catechu followed by M. indica, which was 27.1 and 20.8 mg quercetin equivalents, respectively.

CONCLUSION

Extracts of C. gigantea, E. prostrata, P. persica, U. parviflora, and O. tenuifolium showed antibacterial as well as antibiofilm activity against pathogenic and strong biofilm producing E. coli. Thus, extracts or the pure compound from these medicinal plants could be used as antibiotics in the future.

1-Deoxynojirimycin and its Derivatives: A Mini Review of the Literature

1-Deoxynojirimycin (1-DNJ) is a naturally occurring sugar analogue with unique bioactivities. It is found in mulberry leaves and silkworms, as well as in the metabolites of certain microorganisms, including Streptomyces and Bacillus. 1-DNJ is a potent α-glucosidase inhibitor and it possesses anti-hyperglycemic, anti-obese, anti-viral and anti-tumor properties. Some derivatives of 1-DNJ, like miglitol, miglustat and migalastat, were applied clinically to treat diseases such as diabetes and lysosomal storage disorders. The present review focused on the extraction, determination, pharmacokinetics and bioactivity of 1-DNJ, as well as the clinical application of 1-DNJ derivatives.

Anti-Biofilm Activity of Cell-Free Supernatant of Saccharomyces cerevisiae against Staphylococcus aureus

Staphylococcus aureus is one of the most common microorganisms and causes foodborne diseases. In particular, biofilm-forming S. aureus is more resistant to antimicrobial agents and sanitizing treatments than planktonic cells. Therefore, this study aimed to investigate the anti-biofilm effects of cell-free supernatant (CFS) of Saccharomyces cerevisiae isolated from cucumber jangajji compared to grapefruit seed extract (GSE). CFS and GSE inhibited and degraded S. aureus biofilms. The adhesion ability, auto-aggregation, and exopolysaccharide production of CFS-treated S. aureus, compared to those of the control, were significantly decreased. Moreover, biofilm-related gene expression was altered upon CFS treatment. Scanning electron microscopy images confirmed that CFS exerted anti-biofilm effects against S. aureus. Therefore, these results suggest that S. cerevisiae CFS has anti-biofilm potential against S. aureus strains.

Toward the Identification of Novel Antimicrobial Agents: One-Pot Synthesis of Lipophilic Conjugates of N-Alkyl d- and l-Iminosugars

In the effort to improve the antimicrobial activity of iminosugars, we report the synthesis of lipophilic iminosugars 10a-b and 11a-b based on the one-pot conjugation of both enantiomeric forms of N-butyldeoxynojirimycin (NBDNJ) and N-nonyloxypentyldeoxynojirimycin (NPDNJ) with cholesterol and a succinic acid model linker. The conjugation reaction was tuned using the established PS-TPP/I2/ImH activating system, which provided the desired compounds in high yields (94-96%) by a one-pot procedure. The substantial increase in the lipophilicity of 10a-b and 11a-b is supposed to improve internalization within the bacterial cell, thereby potentially leading to enhanced antimicrobial properties. However, assays are currently hampered by solubility problems; therefore, alternative administration strategies will need to be devised.

Anti-Biofilm Effect of Egg Yolk Phosvitin by Inhibition of Biomass Production and Adherence Activity against Streptococcus mutans

The formation of biofilms on the enamel surface of teeth by Streptococcus mutans is an important step in dental plaque formation, demineralization, and early caries because the biofilm is where other bacteria involved in dental caries attach, grow, and proliferate. The objectives of this study were to determine the effect of phosvitin (PSV) on the biofilm formation, exopolysaccharides (EPS) production, adherence activity of S. mutans, and the expression of genes related to the compounds essential for biofilm formation (quorum-sensing inducers and components of biofilm matrix) by S. mutans. PSV significantly reduced the biofilm-forming activity of S. mutans and increased the degradation of preformed biofilms by S. mutans. PSV inhibited the adherence activity of S. mutans by 31.9%–33.6%, and the production of EPS by 62%–65% depending upon the strains and the amount of PSV added. The expressions of genes regulating the production of EPS and the quorum-sensing-inducers (gtfA, gtfD, ftf, relA, vicR, brpA, and comDE) in all S. mutans strains were down-regulated by PSV, but gtfB was down-regulated only in S. mutans KCTC 5316. Therefore, the anti-biofilm-forming activity of PSV was accomplished through the inhibition of biofilm formation, adherence activity, and the production of quorum-sensing inducers and EPS by S. mutans.

N-Nonyloxypentyl-l-Deoxynojirimycin Inhibits Growth, Biofilm Formation and Virulence Factors Expression of Staphylococcus aureus

Staphylococcus aureus is one of the major causes of hospital- and community-associated bacterial infections throughout the world, which are difficult to treat due to the rising number of drug-resistant strains. New molecules displaying potent activity against this bacterium are urgently needed. In this study, d- and l-deoxynojirimycin (DNJ) and a small library of their N-alkyl derivatives were screened against S. aureus ATCC 29213, with the aim to identify novel candidates with inhibitory potential. Among them, N-nonyloxypentyl-l-DNJ (l-NPDNJ) proved to be the most active compound against S. aureus ATCC 29213 and its clinical isolates, with the minimum inhibitory concentration (MIC) value of 128 μg/mL. l-NPDNJ also displayed an additive effect with gentamicin and oxacillin against the gentamicin- and methicillin-resistant S. aureus isolate 00717. Sub-MIC values of l-NPDNJ affected S. aureus biofilm development in a dose-dependent manner, inducing a strong reduction in biofilm biomass. Moreover, real-time reverse transcriptase PCR analysis revealed that l-NPDNJ effectively inhibited at sub-MIC values the transcription of the spa, hla, hlb and sea virulence genes, as well as the agrA and saeR response regulator genes.

Exploring antibiofilm potential of bacitracin against streptococcus mutans

Bacitracin has well familiar effects on growth and colonization of bacteria but its antibiofilm action on majority of bacteria is still not studied. Bacitracin is a bactericidal antibiotic that primarily acts on Gram positive bacteria by obstructing the process of cell wall synthesis. In this study, we have investigated antibiofilm potential and the mechanism of bacitracin against a cariogenic bacteria 'Streptococcus mutans' which has not been reported so far. Bacitracin has been found to affect propensity of S. mutans to form biofilm. On treatment with sub-MIC concentration of bacitracin resulted in significant reduction in bifilm formation as evaluated by crystal violet and congo red assays. The architecture of S. mutans biofilm was observed by scanning electron microscopy which revealed astonishing phenotype of biofilm. Deficient biofilm was found to be composed of abnormally elongated cells. Transmission electron microscopy showed multiple septa formation in each cell of biofilm thereby indicating, cell division defect as the most probable cause of cell elongation. To elucidate the effect of bacitracin on molecular level, expression profiling of genes critically important for cell division and biofilm formation was performed, which were found many folds downregulated. Bacitracin at very low concentration has been found to have potent antibiofilm activity, therefore is a potential antibiofilm agent to treat oral biofilms. It is being anticipated, this study will offer novel information to identify potential targets and effectively creates true innovation to understand the biofilm's basic biology. Besides, discovering new uses for currently marketed drugs makes commercial as well as research sense.

Antibiofilm activity and cytotoxicity of silk sericin against Streptococcus mutans bacteria in biofilm: an in vitro study

OBJECTIVE

To investigate the potential of sericin extracted by different methods to inhibit biofilm formation (prevention) and disrupt already formed biofilm (treatment).

METHOD

In this in vitro study, sericin was extracted by heat, acid, alkali and urea. Streptococcus mutans bacteria were cultivated in the presence of various concentrations of sericin to evaluate antibiofilm formation using cell density assay (inhibition effect before biofilm formed). Conversely, various concentrations of sericin were added to a biofilm already formed by Streptococcus mutans bacteria, and the viability of bacteria assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay (disruption effects after biofilm formed). Structures of extracted sericin were evaluated using circular dichroism and Fourier-transform infrared spectrometer.

RESULTS

The urea-extracted sericin at all concentrations (12.5mg/ml, 25mg/ml, 50mg/ml and 100mg/ml) showed the highest potential antibiofilm activity in terms of both inhibition and disruption effects, compared with sericin extracted by heat, acid or alkali. The heat-extracted and acid-extracted sericin were found to reduce the biofilm formation dose-dependently, while the alkali-extracted sericin did not show either inhibition or disruption effect on the bacterial biofilm. The urea-extracted sericin also killed the bacteria residing within the biofilm, possibly due to its modified structure which may destabilise the bacterial cell wall, leading to membrane disintegration and, finally, cell death.

CONCLUSION

Our results demostrated the antibiofilm activity of sericin. This could form the basis of further research on the mechanism and application of sericin as a novel antibiofilm agent.

Propolis Affects Pseudomonas aeruginosa Growth, Biofilm Formation, eDNA Release and Phenazine Production: Potential Involvement of Polyphenols

Pseudomonas aeruginosa (P. aeruginosa) is an opportunistic pathogen responsible for a wide range of clinical conditions, from mild infections to life-threatening nosocomial biofilm-associated diseases, which are particularly severe in susceptible individuals. The aim of this in vitro study was to assess the effects of an Albanian propolis on several virulence-related factors of P. aeruginosa, such as growth ability, biofilm formation, extracellular DNA (eDNA) release and phenazine production. To this end, propolis was processed using three different solvents and the extracted polyphenolic compounds were identified by means of high performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS) analysis. As assessed by a bioluminescence-based assay, among the three propolis extracts, the ethanol (EtOH) extract was the most effective in inhibiting both microbial growth and biofilm formation, followed by propylene glycol (PG) and polyethylene glycol 400 (PEG 400) propolis extracts. Furthermore, Pseudomonas exposure to propolis EtOH extract caused a decrease in eDNA release and phenazine production. Finally, caffeic acid phenethyl ester (CAPE) and quercetin decreased upon propolis EtOH extract exposure to bacteria. Overall, our data add new insights on the anti-microbial properties of a natural compound, such as propolis against P. aeruginosa. The potential implications of these findings will be discussed.

Curcumin induced photodynamic therapy mediated suppression of quorum sensing pathway of Pseudomonas aeruginosa: An approach to inhibit biofilm in vitro

OBJECTIVE

The objective of this study was to inhibit the Pseudomonas aeruginosa biofilm through curcumin-mediated antimicrobial photodynamic therapy (A-PDT).

BACKGROUND

The mechanism behind A-PDT mediated photoinactivation depend upon reactive oxygen species (ROS) production, like singlet oxygen and free radicals.

METHODS

To evaluate the antibacterial efficacy of curcumin induced A-PDT on P. aeruginosa by colony forming unit (CFU) while antibiofilm action was determined by the use of crystal violet, XTT, congored binding assay and confocal laser scanning microscope (CLSM).

RESULTS

We found that curcumin with 10 J/cm² of light reduces P. aeruginosa biofilm more efficiently than without light. Extracellular polymeric substances (EPS) production was also reduced by approx 94 % with 10 J/cm² of light dose. CLSM images showed that the thickness of biofilms were reduced from >30 μm to <5 μm after treatment with curcumin followed by 10 J/cm² of light irradiation. Curcumin showed better bacteriostatic activity than bactericidal activity. Singlet oxygen is primarily responsible for photodamage and cytotoxic reactions caused by curcumin-mediated APDT. Genes involved in quorum sensing (QS) pathway was also found to be inhibited after APDT. Curcumin with 5 J/cm² light inhibits QS genes and on increasing light dose i.e10 J/cm², we found a drastic reduction in gene expression.

CONCLUSION

We conclude that the curcumin mediated A-PDT inhibits biofilm formation ofP. aeruginosa through QS pathway by the action of singlet oxygen generation which in turn reduced EPS of the biofilm.

Assessment of alpha glucosidase inhibitors produced from endophytic fungus Alternaria destruens as antimicrobial and antibiofilm agents

Diabetes is considered as a major health concern worldwide and patients with diabetes are at high risk for infectious diseases. Therefore, α-glucosidase inhibitors possessing antibacterial activity along with the ability to inhibit biofilms would be better therapeutic agents for diabetic patients. In the present study, two fractions (AF1 and AF2) possessing α-glucosidase inhibitory activity were purified from an endophytic fungus Alternaria destruens (AKL-3) isolated from Calotropis gigantea. These were evaluated for their antimicrobial and antibiofilm potential against human pathogens. AF1 exhibited broad spectrum antimicrobial activity against all the tested pathogens. It also significantly inhibited biofilm formation and dispersed the preformed biofilm at sub-optimal concentrations. AF2 possessed lesser activity as compared to AF1. The active compounds were purified using semi preparative HPLC. Some of the active compounds were identified to be phenolic in nature. The active fractions were also determined to be non-mutagenic and non-cytotoxic in safety analysis. The study highlights the role of endophytic fungi as sources of α-glucosidase inhibitors with antimicrobial potential which can have application in management of diabetes.

Gymnemic Acids Inhibit Adhesive Nanofibrillar Mediated Streptococcus gordonii-Candida albicans Mono-Species and Dual-Species Biofilms

Dental caries and periodontitis are the most common oral disease of all age groups, affecting billions of people worldwide. These oral diseases are mostly associated with microbial biofilms in the oral cavity. Streptococcus gordonii, an early tooth colonizing bacterium and Candida albicans, an opportunistic pathogenic fungus, are the two abundant oral microbes that form mixed biofilms with augmented virulence, affecting oral health negatively. Understanding the molecular mechanisms of the pathogen interactions and identifying non-toxic compounds that block the growth of biofilms are important steps in the development of effective therapeutic approaches. In this in vitro study we report the inhibition of mono-species or dual-species biofilms of S. gordonii and C. albicans, and decreased levels of biofilm extracellular DNA (eDNA), when biofilms were grown in the presence of gymnemic acids (GAs), a non-toxic small molecule inhibitor of fungal hyphae. Scanning electron microscopic images of biofilms on saliva-coated hydroxyapatite (sHA) surfaces revealed attachment of S. gordonii cells to C. albicans hyphae and to sHA surfaces via nanofibrils only in the untreated control, but not in the GAs-treated biofilms. Interestingly, C. albicans produced fibrillar adhesive structures from hyphae when grown with S. gordonii as a mixed biofilm; addition of GAs abrogated the nanofibrils and reduced the growth of both hyphae and the biofilm. To our knowledge, this is the first report that C. albicans produces adhesive fibrils from hyphae in response to S. gordonii mixed biofilm growth. Semi-quantitative PCR of selected genes related to biofilms from both microbes showed differential expression in control vs. treated biofilms. Further, GAs inhibited the activity of recombinant S. gordonii glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Taken together, our results suggest that S. gordonii stimulates the expression of adhesive materials in C. albicans by direct interaction and/or signaling, and the adhesive material expression can be inhibited by GAs.

Ethnomedicinal Uses of Plant Resources in the Machhapuchchhre Rural Municipality of Kaski District, Nepal

Background: Medicinal plants are being used by the majority of the population throughout the world for their primary health care needs. The reliance is also prevalent in Nepal, aided by its ethnic and biological diversity. This study aimed to catalogue the ethnomedicinal knowledge of plants used by local people of Machhapuchchhre Rural Municipality of Kaski district. Methods: Data were collected between February 2017 and April 2018 from eight different villages of the Kaski district by using semi-structured interviews, guided field works, focus group discussions, and in-depth interviews. The reported traditional uses were supported by local assistants, cataloguing vernacular names and crosschecking with the earlier published and gray literature. Results: A total of 105 medicinal plants, belonging to 58 families and 99 genera were documented to treat 70 different diseases and ailments. The highest numbers of plants (37) were used for gastrointestinal disorders and the lowest (4) were used for female genital disorders. Commonly used parts were underground portions (28 species) followed by fruits and seeds (25 species each). The most preferred dosage form was juice, used for 50 ailments, and the oral route was the most favored route of administration (77 species). The medicinal properties of 22 plant species were found hitherto unreported in the district. Conclusions: The study area was found to be rich in plant resources and the people have ample knowledge on the use of medicinal plants. Due to a lack of proper documentation, conservation, and cultivation practices, valuable plant species are at risk of extinction. Thus, appropriate conservation measures and scientific assessment of plant-lore in the district is immediately required.

10-undecynoic acid is a new anti-adherent agent killing biofilm of oral Streptococcus spp

In the search for novel agents against oral pathogens in their planktonic and biofilm form, we have focused our attention on 10-undecynoic acid as the representative of the acetylenic fatty acids. Using macro-broth susceptibility testing method we first established MIC value. Next, the MBC value was determined from a broth dilution minimum inhibitory concentration test by sub-culturing it to BHI agar plates that did not contain the test agent. Anti-biofilm efficacy was tested in 96-well plates coated with saliva using BHI broth supplemented with 1% sucrose as a standard approach. Based on obtained results, MIC value for 10-undecynoic acid was established to be 2.5 mg/ml and the MBC value to be 5 mg/ml. The MBIC₉₀ showed to be 2.5 mg/ml, however completed inhibition of biofilm formation was achieved at 5.0 mg/ml. MBBC concentration revealed to be the same as MBC value, causing approximately 30% reduction at the same time in biomass of pre-existing biofilm, whereas application of 7.0 mg/ml of 10-undecynoic acid crossed the 50% eradication mark. Strong anti-adherent effect was observed upon 10-undecynoic acid application at sub-MBC concentrations as well, complemented with suppression of acidogenicity and aciduricity. Thus, we concluded that 10-undecynoic acid might play an important role in the development of alternative or adjunctive antibacterial and anti-biofilm preventive and/or therapeutic approaches.

Antimicrobial and Antibiofilm Activity against Streptococcus mutans of Individual and Mixtures of the Main Polyphenolic Compounds Found in Chilean Propolis

Dental caries is multifactorial disease and an important health problem worldwide. Streptococcus mutans is considered as a major cariogenic agent in oral cavity. This bacteria can synthetize soluble and insoluble glucans from sucrose by glucosyltransferases enzymes and generate stable biofilm on the tooth surface. Biological properties of Chilean propolis have been described and it includes antimicrobial, antifungal, and antibiofilm activities. The main goal of this study was to quantify the concentrations of main flavonoids presents in Chilean propolis and compare some biological properties such as antimicrobial and antibiofilm activity of individual compounds and the mixture of this compounds, against S. mutans cultures. Chilean propolis was studied and some polyphenols present in this extract were quantified by HPLC-DAD using commercial standards of apigenin, quercetin, pinocembrin, and caffeic acid phenethyl ester (CAPE). MIC for antimicrobial activity was determined by serial dilution method and biofilm thickness on S. mutans was quantified by confocal microscopy. Pinocembrin, apigenin, quercetin, and caffeic acid phenethyl ester (CAPE) are the most abundant compounds in Chilean propolis. These polyphenols have strong antimicrobial and antibiofilm potential at low concentrations. However, pinocembrin and apigenin have a greater contribution to this action. The effect of polyphenols on S. mutans is produced by a combination of mechanisms to decrease bacterial growth and affect biofilm proliferation due to changes in their architecture.

Spontaneous detachment of Streptococcus mutans biofilm by synergistic effect between zwitterion and sugar alcohol

A biofilm, a community of microorganisms, is highly resistant to antibiotics, resulting in massive losses in various areas. We herein present a strategy to remove Streptococcus mutans biofilms through a spontaneous exfoliation by the synergistic effect between zwitterion and sugar alcohols. It is assumed that the anionic site of zwitterion can be coupled with sugar alcohols and the cationic site remains in the state of lacking electrons. The cationic site allows the complexes to be delivered to negatively charged exopolysaccharides of biofilms. This strategy facilitates a significant increase in the ability of sugar alcohols to disperse aggregated exopolysaccharides. In this work, it was demonstrated that the mixture of betaine and erythritol existed as a complex in water and that the complex induced a spontaneous detachment of biofilms from the surface to which the biofilms had been adhered. This detachment resulted from a reduction in adhesive forces of the biofilms due to an increase in solubility of bacterial exopolysaccharides. The effects triggered by the formation of complex between zwitterion and sugar alcohol provide a simple and safe way to remove biofilms without antibiotics and physical forces.

Rutin Inhibits Streptococcus suis Biofilm Formation by Affecting CPS Biosynthesis

Streptococcus suis (S. suis) form biofilms and causes severe diseases in humans and pigs. Biofilms are communities of microbes embedded in a matrix of extracellular polymeric substances. Eradicating biofilms with the use of antibiotics or biocides is often ineffective and needs replacement with other potential agents. Compared to conventional agents, promising and potential alternatives are biofilm-inhibiting compounds without impairing growth. Here, we screened a S. suis adhesion inhibitor, rutin, derived from Syringa. Rutin, a kind of flavonoids, shows efficient biofilm inhibition of S. suis without impairing its growth. Capsular polysaccharides(CPS) are reported to be involved in its adherence to influence bacterial biofilm formation. We investigated the effect of rutin on S. suis CPS content and structure. The results showed that rutin was beneficial to improve the CPS content of S. suis without changing its structure. We further provided evidence that rutin specifically affected S. suis biofilm susceptibility by affecting CPS biosynthesis in vitro. The study explores the antibiofilm potential of rutin against S. suis which can be used as an adhesion inhibitor for the prevention of S. suis biofilm-related infections. Nevertheless, rutin could be used as a novel natural inhibitor of biolfilm and its molecular mechanism provide basis for its pharmacological and clinical applications.

Betulin inhibits cariogenic properties of Streptococcus mutans by targeting vicRK and gtf genes

Streptococcus mutans, a multivirulent pathogen is considered the primary etiological agent in dental caries. Development of antibiotic resistance in the pathogen has created a need for novel antagonistic agents which can control the virulence of the organism and reduce resistance development. The present study demonstrates the in vitro anti-virulence potential of betulin (lup-20(29)-ene-3β,28-diol), an abundantly available plant triterpenoid against S. mutans UA159. Betulin exhibited significant dose dependent antibiofilm activity without affecting bacterial viability. At 240 µg/ml (biofilm inhibitory concentration), betulin inhibited biofilm formation and adherence to smooth glass surfaces by 93 and 71 % respectively. It reduced water insoluble glucan synthesis by 89 %, in conjunction with down regulation of gtfBC genes. Microscopic analysis confirmed the disruption in biofilm architecture and decreased exopolysaccharide production. Acidogenicity and aciduricity, key virulence factors responsible for carious lesions, were also notably affected. The induced auto-aggregation of cells upon treatment could be due to the down regulation of vicK. Results of gene expression analysis demonstrated significant down-regulation of virulence genes upon betulin treatment. Furthermore, the nontoxic effect of betulin on peripheral blood mononuclear cells even after 72 h treatment makes it a strong candidate for assessing its suitability to be used as a therapeutic agent.

New potential phytotherapeutics obtained from white mulberry (Morus alba L.) leaves

The present work demonstrates the profound and unique phyto-pharmacological and nutritional profile of white mulberry (Morus alba L.) leaves which containing considerable amounts of easy digestive proteins, carbohydrates, micro- and macronutrients, polyphenols, free amino acids, organic acids. The wide range of significant biopharmaceutical activities of the aqueous and polar organic solvents extracts from mulberry leaves - including antidiabetic, antibacterial, anticancer, cardiovascular, hypolipidemic, antioxidant, antiatherogenic, and anti-inflammatory - have been critically discussed. The main objective was to demonstrate the results of recently published study on the components of white mulberry leaves exhibiting their biological activity in the various pathological and health human ailments. In addition, we intend to drawn the attention of researchers and public health workers for the extended exploration of this deciduous plant leaves as the source of potential indigenous nutraceuticals and functional food products to enable development of alternative prevention and treatment protocols offered in therapy of the common non-communicable diseases and malignances.

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.

Effects of the Selected Iminosugar Derivatives on Pseudomonas aeruginosa Biofilm Formation

A lack of an effective way to eliminate pathogenic bacteria hidden in the biofilm is a major problem in the treatment of chronic bacterial infections. Iminosugar derivatives are potential candidates for inhibitors of enzymes taking part in the biosynthesis of exopolysaccharides, which are forming bacterial biofilm. Investigated iminosugars were studied either at an early stage of biofilm formation or later on when the mature biofilm of Pseudomonas aeruginosa was already formed. A series of diverse iminosugar structures significantly inhibited biofilm formation, whereas they showed no influence on already formed biofilm. This indicates a possible mechanism of their action based on inhibition of exopolysaccharide backbone synthesis in the early stages of biofilm formation. Moreover, iminosugar derivatives did not show significant effect on the viable bacterial numbers in both early and mature biofilm forms. Importantly, they were not cytotoxic against human Caco-2 cells in vitro, which may be to their advantage in case of their medical application in preventing P. aeruginosa biofilm formation.

Polyphenol-Rich Extract from Propolis Reduces the Expression and Activity of Streptococcus mutans Glucosyltransferases at Subinhibitory Concentrations

Tooth decay is an infectious disease, whose main causative agent identified is Streptococcus mutans (S. mutans). Diverse treatments have been used to eradicate this microorganism, including propolis. To date, it has been shown that polyphenols from Chilean propolis inhibit S. mutans growth and biofilm formation. However, the molecular mechanisms underlying this process are unclear. In the present study, we assessed the effect of Chilean propolis on the expression and activity of the glycosyltransferases enzymes and their related genes. Polyphenol-rich extract from propolis inhibited gene expression of glycosyltransferases (GtfB, GtfC, and GtfD) and their related regulatory genes, for example, VicK, VicR, and CcpA. Moreover, the treatment inhibited glucosyltransferases activity measured by the formation of sucrose-derived glucans. Additionally, an inhibitory effect was observed in the expression of SpaP involved in sucrose-independent virulence of S. mutans. In summary, our results suggest that Chilean propolis has a dose-dependent effect on the inhibition of genes involved in S. mutans virulence and adherence through the inhibition of glucosyltransferases, showing an anticariogenic potential of polyphenols from propolis beyond S. mutans growth inhibition.

Plants and other natural products used in the management of oral infections and improvement of oral health

Challenges of resistance to synthetic antimicrobials have opened new vistas in the search for natural products. This article rigorously reviews plants and other natural products used in oral health: Punica granatum L. (pomegranate), Matricaria recutita L. (chamomile), Camellia sinensis (L.) Kuntze (green tea), chewing sticks made from Diospyros mespiliformis Hochst. ex A.D.C., Diospyros lycioides Desf., and Salvadora persica L. (miswak), honey and propolis from the manuka tree (Leptospermum scoparium J.R. Forst. & G. Forst.), rhein from Rheum rhabarbarum L. (rhubarb), dried fruits of Vitis vinifera L. (raisins), essential oils, probiotics and mushrooms. Further, the review highlights plants from Africa, Asia, Brazil, Mexico, Europe, and the Middle East. Some of the plants' antimicrobial properties and chemical principles have been elucidated. While the use of natural products for oral health is prominent in resource-poor settings, antimicrobial testing is mainly conducted in the following countries (in decreasing order of magnitude): India, South Africa, Brazil, Japan, France, Egypt, Iran, Mexico, Kenya, Switzerland, Nigeria, Australia, Uganda, and the United Kingdom. While the review exposes a dire gap for more studies on clinical efficacy and toxicity, the following emerging trend was noted: basic research on plants for oral health is mainly done in Brazil, Europe and Australia. Brazil, China, India and New Zealand generally conduct value addition of natural products for fortification of toothpastes. African countries focus on bioprospecting and primary production of raw plants and other natural products with antimicrobial efficacies. The Middle East and Egypt predominantly research on plants used as chewing sticks. More research and funding are needed in the field of natural products for oral health, especially in Africa where oral diseases are fuelled by human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS).

Natural Antimicrobials and Oral Microorganisms: A Systematic Review on Herbal Interventions for the Eradication of Multispecies Oral Biofilms

Oral diseases such as caries and periodontitis are mainly caused by microbial biofilms. Antibiotic therapy has reached its limits with regard to antimicrobial resistance, and new therapeutic measures utilizing natural phytochemicals are currently a focus of research. Hence, this systematic review provides a critical presentation of the antimicrobial effects of various medicinal herbs against in vitro, ex vivo, and in situ formed multispecies oral biofilms. Searches were performed in three English databases (PubMed, EMBASE, CAMbase) and the electronic archives of five German journals from the times of their establishment until October 10th, 2014, with the search terms “(plant extracts OR herbal extracts OR plant OR herb) AND (oral biofilm OR dental biofilm OR dental plaque OR oral disease OR dental disease).” The pooled data were assessed according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines (PRISMA). Initially, 1848 articles were identified, out of which 585 full-text articles were screened, 149 articles were reevaluated for eligibility and finally, 14 articles met all inclusion criteria. The data of 14 reports disclosed enhanced antiadhesive and antibiofilm activity by the plant extracts obtained from Vitis vinifera, Pinus spp., Coffea canephora, Camellia sinensis, Vaccinium macrocarpon, Galla chinensis, Caesalpinia ferrea Martius, Psidium cattleianum, representative Brazilian plants and manuka honey. Overall, a positive correlation was revealed between herb-based therapies and elimination rates of all types of multispecies oral biofilms. In that context, integrating or even replacing conventional dental therapy protocols with herbal-inspired treatments can allow effective antimicrobial control of oral biofilms and thus, dental diseases.

Antibiofilm action of a toluidine blue O-silver nanoparticle conjugate on Streptococcus mutans: a mechanism of type I photodynamic therapy

The objective of this study was to evaluate the anti-biofilm efficacy of photodynamic therapy by conjugating a photosensitizer (TBO) with silver nanoparticles (AgNP). Streptococcus mutans was exposed to laser light (630 nm) for 70 s (9.1 J cm(-2)) in the presence of a toluidine blue O-silver nanoparticle conjugate (TBO-AgNP). The results showed a reduction in the viability of bacterial cells by 4 log10. The crystal violet assay, confocal laser scanning microscopy and scanning electron microscopy revealed that the TBO-AgNP conjugates inhibited biofilm formation, increased the uptake of propidium iodide and leakage of the cellular constituents, respectively. Fluorescence spectroscopic studies confirmed the generation of OH(•) as a major reactive oxygen species, indicating type I phototoxicity. Both the conjugates down-regulated the expression of biofilm related genes compared to TBO alone. Hence TBO-AgNP conjugates were found to be more phototoxic against S. mutans biofilm than TBO alone.

Nanoparticles vs. biofilms: a battle against another paradigm of antibiotic resistance

Microbes form surface-adherent community structures called biofilms and these biofilms play a critical role in infection.

Calcium fluoride nanoparticles induced suppression of Streptococcus mutans biofilm: an in vitro and in vivo approach

Biofilm formation on the tooth surface is the root cause of dental caries and periodontal diseases. Streptococcus mutans is known to produce biofilm which is one of the primary causes of dental caries. Acid production and acid tolerance along with exopolysaccharide (EPS) formation are major virulence factors of S. mutans biofilm. In the current study, calcium fluoride nanoparticles (CaF2-NPs) were evaluated for their effect on the biofilm forming ability of S. mutans in vivo and in vitro. The in vitro studies revealed 89 % and 90 % reduction in biofilm formation and EPS production, respectively. Moreover, acid production and acid tolerance abilities of S. mutans were also reduced considerably in the presence of CaF2-NPs. Confocal laser scanning microscopy and transmission electron microscopy images were in accordance with the other results indicating inhibition of biofilm without affecting bacterial viability. The qRT-PCR gene expression analysis showed significant downregulation of various virulence genes (vicR, gtfC, ftf, spaP, comDE) associated with biofilm formation. Furthermore, CaF2-NPs were found to substantially decrease the caries in treated rat groups as compared to the untreated groups in in vivo studies. Scanning electron micrographs of rat's teeth further validated our results. These findings suggest that the CaF2-NPs may be used as a potential antibiofilm applicant against S. mutans and may be applied as a topical agent to reduce dental caries.

Biofilms as "Connectors" for Oral and Systems Medicine: A New Opportunity for Biomarkers, Molecular Targets, and Bacterial Eradication

Oral health and systems medicine are intimately related but have remained, sadly, as isolated knowledge communities for decades. Are there veritable connector knowledge domains that can usefully link them together on the critical path to biomarker research and “one health”? In this context, it is noteworthy that bacteria form surface-attached communities on most biological surfaces, including the oral cavity. Biofilm-forming bacteria contribute to periodontal diseases and recent evidences point to roles of these bacteria in systemic diseases as well, with cardiovascular diseases, obesity, and cancer as notable examples. Interestingly, the combined mass of microorganisms such as bacteria are so large that when we combine all plants and animals on earth, the total biomass of bacteria is still bigger. They literally do colonize everywhere, not only soil and water but our skin, digestive tract, and even oral cavity are colonized by bacteria. Hence efforts to delineate biofilm formation mechanisms of oral bacteria and microorganisms and the development of small molecules to inhibit biofilm formation in the oral cavity is very timely for both diagnostics and therapeutics. Research on biofilms can benefit both oral and systems medicine. Here, we examine, review, and synthesize new knowledge on the current understanding of oral biofilm formation, the small molecule targets that can inhibit biofilm formation in the mouth. We suggest new directions for both oral and systems medicine, using various omics technologies such as SILAC and RNAseq, that could yield deeper insights, biomarkers, and molecular targets to design small molecules that selectively aim at eradication of pathogenic oral bacteria. Ultimately, devising new ways to control and eradicate bacteria in biofilms will open up novel diagnostic and therapeutic avenues for oral and systemic diseases alike.