Inhibition of suilysin activity and inflammation by myricetin attenuates Streptococcus suis virulence

Natural Antimicrobial Compounds as Promising Preservatives: A Look at an Old Problem from New Perspectives

Antimicrobial compounds of natural origin are of interest because of the large number of reports regarding the harmfulness of food preservatives. These natural products can be derived from plants, animal sources, microorganisms, algae, or mushrooms. The aim of this review is to consider known antimicrobials of natural origin and the mechanisms of their action, antimicrobial photodynamic technology, and ultrasound for disinfection. Plant extracts and their active compounds, chitosan and chitosan oligosaccharide, bioactive peptides, and essential oils are highly potent preservatives. It has been experimentally proven that they possess strong antibacterial capabilities against bacteria, yeast, and fungi, indicating the possibility of their use in the future to create preservatives for the pharmaceutical, agricultural, and food industries.

Myricetin Acts as an Inhibitor of Type II NADH Dehydrogenase from Staphylococcus aureus

BACKGROUND

Staphylococcus aureus is a common pathogenic microorganism in humans and animals. Type II NADH oxidoreductase (NDH-2) is the only NADH:quinone oxidoreductase present in this organism and represents a promising target for the development of anti-staphylococcal drugs. Recently, myricetin, a natural flavonoid from vegetables and fruits, was found to be a potential inhibitor of NDH-2 of S. aureus. The objective of this study was to evaluate the inhibitory properties of myricetin against NDH-2 and its impact on the growth and expression of virulence factors in S. aureus.

RESULTS

A screening method was established to identify effective inhibitors of NDH-2, based on heterologously expressed S. aureus NDH-2. Myricetin was found to be an effective inhibitor of NDH-2 with a half maximal inhibitory concentration (IC50) of 2 μM. In silico predictions and enzyme inhibition kinetics further characterized myricetin as a competitive inhibitor of NDH-2 with respect to the substrate menadione (MK). The minimum inhibitory concentrations (MICs) of myricetin against S. aureus strains ranged from 64 to 128 μg/mL. Time-kill assays showed that myricetin was a bactericidal agent against S. aureus. In line with being a competitive inhibitor of the NDH-2 substrate MK, the anti-staphylococcal activity of myricetin was antagonized by MK-4. In addition, myricetin was found to inhibit the gene expression of enterotoxin SeA and reduce the hemolytic activity induced by S. aureus culture on rabbit erythrocytes in a dose-dependent manner.

CONCLUSIONS

Myricetin was newly discovered to be a competitive inhibitor of S. aureus NDH-2 in relation to the substrate MK. This discovery offers a fresh perspective on the anti-staphylococcal activity of myricetin.

Ultrasound-assisted extraction of emodin from Rheum officinale Baill and its antibacterial mechanism against Streptococcus suis based on CcpA

Emodin was extracted from Rheum officinale Baill by ultrasound-assisted extraction (UAE), and ethanol was chosen as the suitable solvent through SEM and molecular dynamic simulation. Under the optimum conditions (power 541 W, time 23 min, liquid to material ratio 13:1 mL/g, ethanol concentration 83 %) predicted by RSM, the yield of emodin was 2.18 ± 0.11 mg/g. Moreover, ultrasound power and time displayed the significant effects on the extraction process. Extracting dynamics analysis indicated that the extraction process of emodin by UAE conformed to Fick's second diffusion law. The results of antibacterial experiments suggested that emodin can damage cell membrane and inhibit the expression of cps2A, sao, mrp, epf, neu and the hemolytic activity of S. suis. Biolayer interferometry and FT-IR multi-peak fitting assays demonstrated that emodin induced a secondary conformational shift in CcpA. Molecular docking and molecular dynamics confirmed that emodin bound to CcpA through hydrogen bonding (ALA248, GLU249, GLY129 and ASN196) and π-π T-shaped interaction (TYR225 and TYR130), and the mutation of amino acid residues affected the affinity of CcpA to emodin. Therefore, emodin inhibited the sugar utilization of S. suis through binding to CcpA, and CcpA may be a potential target to inhibit the growth of S. suis.

Transcriptional Host Responses to Infection with Streptococcus suis in a Porcine Precision-Cut Lung Slice Model: Between-Strain Differences Suggest Association with Virulence Potential

Streptococcus suis is a porcine and zoonotic pathogen in the upper respiratory tract, expressing different capsular serotypes and virulence-associated factors. Given its genomic and phenotypic diversity, the virulence potential of S. suis cannot be attributed to a single factor. Since strong inflammatory response is a hallmark of S. suis infection, the objective of this study was to investigate the differences in transcriptional host responses to two serotype 2 and one serotype 9 strains. Both serotypes are frequently found in clinical isolates. We infected porcine precision-cut lung slices (PCLSs) with two serotype 2 strains of high (strain S10) and low (strain T15) virulence, and a serotype 9 strain 8067 of moderate virulence. We observed higher expression of inflammation-related genes during early infection with strains T15 and 8067, in contrast to infection with strain 10, whose expression peaked late. In addition, bacterial gene expression from infected PCLSs revealed differences, mainly of metabolism-related and certain virulence-associated bacterial genes amongst these strains. We conclude that the strain- and time-dependent induction of genes involved in innate immune response might reflect clinical outcomes of infection in vivo, implying rapid control of infection with less virulent strains compared to the highly virulent strain S10.

Cholesterol dependent cytolysins and the brain: Revealing a potential therapeutic avenue for bacterial meningitis

Bacterial meningitis is a catastrophic nervous system disorder with high mortality and wide range of morbidities. Some of the meningitis-causing bacteria occupy cholesterol dependent cytolysins (CDCs) to increase their pathogenicity and arrange immune-evasion strategy. Studies have observed that the relationship between CDCs and pathogenicity in these meningitides is complex and involves interactions between CDC, blood-brain barrier (BBB), glial cells and neurons. In BBB, these CDCs acts on capillary endothelium, tight junction (TJ) proteins and neurovascular unit (NVU). CDCs also observed to elicit intriguing effects on brain inflammation which involves microglia and astrocyte activations, along with neuronal damage as the end-point of pathological pathways in bacterial meningitis. As some studies mentioned potential advantage of CDC-targeted therapeutic mechanisms to combat CNS infections, it might be a fruitful avenue to deepen our understanding of CDC as a candidate for adjuvant therapy to combat bacterial meningitis.

Vimentin affects inflammation and neutrophil recruitment in airway epithelium during Streptococcus suis serotype 2 infection

Streptococcus suis serotype 2 (SS2) frequently colonizes the swine upper respiratory tract and can cause Streptococcal disease in swine with clinical manifestations of pneumonia, meningitis, and septicemia. Previously, we have shown that vimentin, a kind of intermediate filament protein, is involved in the penetration of SS2 through the tracheal epithelial barrier. The initiation of invasive disease is closely related to SS2-induced excessive local inflammation; however, the role of vimentin in airway epithelial inflammation remains unclear. Here, we show that vimentin deficient mice exhibit attenuated lung injury, diminished production of proinflammatory cytokines interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α), and the IL-8 homolog, keratinocyte-derived chemokine (KC), and substantially reduced neutrophils in the lungs following intranasal infection with SS2. We also found that swine tracheal epithelial cells (STEC) without vimentin show decreased transcription of IL-6, TNF-α, and IL-8. SS2 infection caused reassembly of vimentin in STEC, and pharmacological disruption of vimentin filaments prevented the transcription of those proinflammatory cytokines. Furthermore, deficiency of vimentin failed to increase the transcription of nucleotide oligomerization domain protein 2 (NOD2), which is known to interact with vimentin, and the phosphorylation of NF-κB protein p65. This study provides insights into how vimentin promotes excessive airway inflammation, thereby exacerbating airway injury and SS2-induced systemic infection.

Melatonin Maintains Homeostasis and Potentiates the Anti-inflammatory Response in Staphylococcus aureus-Induced Mastitis through microRNA-16b/YAP1

Staphylococcus aureus is a highly infectious pathogen and is a considerable threat to food hygiene and safety. Although melatonin is thought to exert an ameliorative effect on bovine mastitis, the regulatory mechanisms are unclear. In this study, we first verified the therapeutic effect of melatonin against S. aureus in vitro and in vivo, a screening of differentially expressed miRNAs and mRNAs among the blank, and S. aureus and melatonin + S. aureus groups by high-throughput sequencing identified miR-16b and YAP1, which exhibited 1.95-fold upregulated and 1.05-fold downregulated expression, respectively. Moreover, epigenetic studies showed that S. aureus inhibited miR-16b expression by methylation (increased DNMT1 expression). Additionally, the DNMT1 expression level was significantly decreased by melatonin treatment, which might indicate that the inhibition of DNMT1 by melatonin reduces the effect of S. aureus on miR-16b. The flow cytometry, scanning and transmission electron microscopy, EdU assay, and cell morphology results indicated that miR-16b in bovine mammary epithelial cells (in vitro) and in mice (in vivo) can modulate the maintenance of homeostasis and potentiate the anti-inflammatory response. In addition, YAP1 was demonstrated to be the target gene of miR-16b through quantitative real-time polymerase chain reaction, western blot, RNA immunoprecipitation, and functional assays. This study indicates that melatonin inhibits S. aureus-induced inflammation via microRNA-16b/YAP1-mediated regulation, and these findings might provide a new strategy for the prevention of bovine mastitis, facilitating further studies good of zoonotic diseases caused by S. aureus infection.

Acacetin attenuates Streptococcus suis virulence by simultaneously targeting suilysin and inflammation

Streptococcus suis (S. suis), an important zoonotic pathogenic bacterium, can cause multiple diseases and fatal infections in both humans and animals. The emergence of highly virulent and extensively drug-resistant strains of S. suis has raised questions about the efficacy of available therapeutic agents, thereby necessitating novel therapeutic strategies. Suilysin (SLY) is one of the most essential determinants of virulence for the pathogenicity of S. suis capsular type 2 (SS2). In addition, inhibiting the excessive inflammatory response is a strategy to reduce the damage caused by SS2 infection. In this study, we identified acacetin as an effective inhibitor of SLY, which inhibited the oligomerisation of SLY without affecting bacterial growth. Furthermore, the addition of 4-16 μg/ml acacetin to the co-infection system of the cells reduced S. suis-induced inflammation by downregulating the activation of the MAPK signalling pathway, thereby alleviating the S. suis-mediated cell injury. Thus, in addition to the conventional antibiotic therapy, acacetin represent a potential drug candidate and strategy for the treatment of S. suis infections as it simultaneously inhibited the haemolytic activity of SLY and downregulated the inflammatory response.

Acquiring high expression of suilysin enable non-epidemic Streptococccus suis to cause streptococcal toxic shock-like syndrome (STSLS) through NLRP3 inflammasome hyperactivation

The epidemic Streptococcus suis (S. suis) strain [Sequence type (ST) 7] was gradually evolving from the non-epidemic ST1 strain and got the ability for high expressing of suilysin (SLY). And the high expression of SLY was required for the epidemic strain to cause NLRP3 hyperactivation, which is essential for the induction of cytokines storm, dysfunction of multiple organs, and a high incidence of mortality, the characters of streptococcal toxic shock-like syndrome (STSLS). However, it remains to be elucidated whether acquiring high SLY expression due to genome evolution was sufficient for the non-epidemic strain to cause STSLS. Here, we found that the overexpression of SLY in ST1 strain (P1/7-SLY) could obviously increase the inflammasome activation, which was dependent on NLRP3 signalling. In contrast, the strain (P1/7-mSLY) overexpressing the mutant SLY (protein without hemolytic activity) could not significantly increase the inflammasome activation. Furthermore, similar to the epidemic strain, P1/7-SLY could cause STSLS in nlrp3^+/+ mice but not in nlrp3^−/− mice. In contrast, P1/7-mSLY could not cause STSLS in both nlrp3^+/+ mice and nlrp3^−/− mice. In summary, we demonstrate that genetic evolution enabling S. suis strain to express high level of SLY may be an essential and sufficient condition for NLRP3 inflammasome hyperactivation, which could further cause cytokines storm and STSLS.

Myricetin as an Antivirulence Compound Interfering with a Morphological Transformation into Coccoid Forms and Potentiating Activity of Antibiotics against Helicobacter pylori

Helicobacter pylori, a gastric pathogen associated with a broad range of stomach diseases, has a high tendency to become resistant to antibiotics. One of the most important factors related to therapeutic failures is its ability to change from a spiral to a coccoid form. Therefore, the main aim of our original article was to determine the influence of myricetin, a natural compound with an antivirulence action, on the morphological transformation of H. pylori and check the potential of myricetin to increase the activity of antibiotics against this pathogen. We observed that sub-minimal inhibitory concentrations (sub-MICs) of this compound have the ability to slow down the process of transformation into coccoid forms and reduce biofilm formation of this bacterium. Using checkerboard assays, we noticed that the exposure of H. pylori to sub-MICs of myricetin enabled a 4–16-fold reduction in MICs of all classically used antibiotics (amoxicillin, clarithromycin, tetracycline, metronidazole, and levofloxacin). Additionally, RT-qPCR studies of genes related to the H. pylori morphogenesis showed a decrease in their expression during exposure to myricetin. This inhibitory effect was more strongly seen for genes involved in the muropeptide monomers shortening (csd3, csd6, csd4, and amiA), suggesting their significant participation in the spiral-to-coccoid transition. To our knowledge, this is the first research showing the ability of any compound to synergistically interact with all five antibiotics against H. pylori and the first one showing the capacity of a natural substance to interfere with the morphological transition of H. pylori from spiral to coccoid forms.

Eco-Friendly and Facile Synthesis of Antioxidant, Antibacterial and Anticancer Dihydromyricetin-Mediated Silver Nanoparticles

Background

Dihydromyricetin (DMY), a natural flavonoid, has reportedly antibacterial, antioxidant, anticancer and other properties. In the present study, DMY was used as a reducing agent and stabilizer to synthesize silver nanoparticles (AgNPs), and the optimal conditions for its synthesis were studied. The DMY-AgNPs were investigated for their DPPH scavenging properties and their potential against human pathogenic and food-borne bacteria viz. Escherichia coli (E. coli), and Salmonella. In addition, DMY-AgNPs also showed excellent inhibitory effects on cancer Hela, HepG2 and MDA-MB-231 cell lines.

Methods

The dihydromyricetin-mediated AgNPs (DMY-AgNPs) were characterized by ultraviolet-visible spectrophotometer (UV-Vis spectra), scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD). Antioxidant activity of DMY-AgNPs was determined by 1.1-diphenyl-2-picrylhydrazyl (DPPH) scavenging. The antibacterial activity was determined by 96-well plate (AGAR) gradient dilution, while anticancer potential was determined by MTT assay.

Results

The results showed that the dispersion of AgNPs had the maximum UV-visible absorption at about 410 nm. The synthesized nanoparticles were almost spherical. FTIR was used to identify functional groups that may lead to the transformation of metal ions into nanoparticles. The results showed that the prepared AgNPs were coated with biological molecules in the extraction solution. The biosynthesized DMY-AgNPs exhibited good antioxidant properties, at various concentrations (0.01-0.1mg/mL), the free radical scavenging rate was about 56-92%. Furthermore, DMY-AgNPs possessed good antibacterial properties against Escherichia coli (E. coli), and Salmonella at room temperature. The minimum inhibitory concentrations (MIC) were 10^-6 g/L, and 10^-4 g/L, respectively. The bioactivity of DMY-mediated AgNPs was studied using MTT assay against Hela, HepG2 and MDA-MB-231 cancer cell lines, and all showed good inhibitory effects.

Conclusion

The present study provides a green approach for the synthesis of DMY-AgNPs which exhibited stronger antioxidant, antibacterial and anticancer properties compared to the dihydromyricetin. DMY-AgNPs can serve as an economical, efficient, and effective antimicrobial material for its applications in food and pharmaceutical fields.

Green and Facile Synthesis and Antioxidant and Antibacterial Evaluation of Dietary Myricetin-Mediated Silver Nanoparticles

Myricetin (MY) is a dietary flavonoid which exhibits a wide spectrum of biological properties, viz., antibacterial, antioxidant, anticancer, and so forth. The lower solubility in aqueous medium and hence lesser bioavailability of MY limits the use of such dietary flavonoids in further in vivo research. To overcome bioavailability limitations, a number of drug-delivery systems are being investigated. Herein, MY-mediated silver nanoparticles (MY-AgNPs) were synthesized by a green approach to improve the therapeutic efficacy of MY. MY-AgNPs were characterized by ultraviolet-visible spectroscopy (UV-Vis), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and X-ray powder diffraction (XRD). The results showed that the dispersion of AgNPs had the maximum UV-vis absorption at about 410 nm. The synthesized nanoparticles were almost spherical. MY-AgNPs were further investigated against human pathogenic bacteria, and their antioxidant potential was also determined. The free radical scavenging rate was about 60-87%. MY-AgNPs had good antibacterial activity against Escherichia coli and Salmonella at room temperature with minimum inhibitory concentrations of 10-4 and 10-5 g/L, respectively.

Myricetin: A review of the most recent research

Myricetin(MYR) is a flavonoid compound widely found in many natural plants including bayberry. So far, MYR has been proven to have multiple biological functions and it is a natural compound with promising research and development prospects. This review comprehensively retrieved and collected the latest pharmacological abstracts on MYR, and discussed the potential molecular mechanisms of its effects. The results of our review indicated that MYR has a therapeutic effect on many diseases, including tumors of different types, inflammatory diseases, atherosclerosis, thrombosis, cerebral ischemia, diabetes, Alzheimer's disease and pathogenic microbial infections. Furthermore, it regulates the expression of Hippo, MAPK, GSK-3β, PI3K/AKT/mTOR, STAT3, TLR, IκB/NF-κB, Nrf2/HO-1, ACE, eNOS / NO, AChE and BrdU/NeuN. MYR also enhances the immunomodulatory functions, suppresses cytokine storms, improves cardiac dysfunction, possesses an antiviral potential, can be used as an adjuvant treatment against cancer, cardiovascular injury and nervous system diseases, and it may be a potential drug against COVID-19 and other viral infections. Generally, this article provides a theoretical basis for the clinical application of MYR and a reference for its further use.

Contribution of Nlrp3 Inflammasome Activation Mediated by Suilysin to Streptococcal Toxic Shock-like Syndrome

Objective: The aim of this study was to investigate the molecular mechanism of inflammasome activation in response to Streptococcus suis serotype 2 (SS2) infection and its contribution to the development of streptococcal toxic shock-like syndrome (STSS).

Methods: To verify the role of suilysin (SLY) in STSS, we infected bone-marrow-derived macrophages (BMDMs) in vitro and C57BL/6J mice intraperitoneally (IP) with the SS2 wild-type (WT) strain or isogenic sly mutant (∆SLY) to measure the interleukin (IL)-1β release and survival rate. To determine the role of inflammasome activation and pyroptosis in STSS, we infected BMDMs from WT and various deficient mice, including Nlrp3-deficient (Nlrp3^−/−), Nlrc4-deficient (Nlrc4^−/−), Asc-deficient (Asc^−/−), Aim2-deficient (Aim2^−/−), Caspase-1/11-deficient (Caspase-1/11^−/−), and Gsdmd-deficient (Gsdmd^−/−) ex vivo, and IP injected WT, Nlrp3^−/−, Caspase-1/11^−/−, and Gsdmd^−/− mice with SS2, to compare the IL-1β releases and survival rate in vivo.

Results: The SS2-induced IL-1β production in mouse macrophages is mediated by SLY ex vivo. The survival rate of WT mice infected with SS2 was significantly lower than that of mice infected with the ∆SLY strain in vivo. Furthermore, SS2-triggered IL-1β releases, and the cytotoxicity in the BMDMs required the activation of the NOD-Like Receptors Family Pyrin Domain Containing 3 (Nlrp3), Caspase-1/11, and gasdermin D (Gsdmd) inflammasomes, but not the Nlrc4 and Aim2 inflammasomes ex vivo. The IL-1β production and survival rate of WT mice infected with SS2 were significantly lower than those of the Nlrp3^−/−, Caspase-1/11^−/−, and Gsdmd^−/− mice in vivo. Finally, the inhibitor of the Nlrp3 inflammasome could reduce the IL-1β release and cytotoxicity of SS2-infected macrophages ex vivo and protect SS2-infected mice from death in vivo.

Conclusion: Nlrp3 inflammasome activation triggered by SLY in macrophages played an important role in the pathogenesis of STSS.

Identification and pathogenicity analysis of Streptococcus equinus FMD1, a beta-hemolytic strain isolated from forest musk deer lung

Streptococcus spp. cause a wide range of diseases in animals and humans. A Streptococcus strain (FMD1) was isolated from forest musk deer lung. To identify the bacterium at the species level and investigate its pathogenicity, whole genome sequencing and experimental infections of mice were performed. The genome had 97.63% average nucleotide identity with the S. equinus strain. Through virulence gene analysis, a beta-hemolysin/cytolysin genome island was found in the FMD1 genome, which contained 12 beta-hemolysin/cytolysin-related genes. Hemolytic reaction and histopathological analysis established the strain’s pathogenicity in mice. This is the first report of a beta-hemolytic S. equinus strain in forest musk deer identified based on phenotypic and genotypic analyzes; this strategy could be useful for analyzing pathogens affecting rare animals.

Anti-tumor effects and associated molecular mechanisms of myricetin

Myricetin (3, 5, 7, 3', 4', 5'-hexahydroxyflavone) is a natural flavonol compound found in a large variety of plants, including berries, oranges, grapes, herbs, teas, and wine. In the last decade, a convergence of evidence has demonstrated that myricetin has good biological activity as an anti-tumor, anti-inflammatory, and anti-oxidation agent. In studies involving various types of cancer cells, myricetin has been shown to suppress cancer cell invasion and metastasis, to induce cell cycle arrest and apoptosis of cancer cells, and to inhibit their proliferation. These findings have raised interest in myricetin as a potential tumor inhibitor in human patients. In this review, evidence of myricetin's anti-tumor activity and its underlying molecular mechanisms published in the last decade are summarized.