Subinhibitory concentrations of resveratrol reduce alpha-hemolysin production in Staphylococcus aureus isolates by downregulating saeRS

Pt-Induced Sublattice Distortion Facilitates Enzyme Cascade Reactions for Eradicating Intracellularly Methicillin-Resistant Staphylococcus aureus and Enhancing Diabetic Wound Healing

Metal oxide nanozymes hold significant potential in combating bacterial infections; however, their ordered crystal structures limit the enhancement of catalytic activity, posing challenges in addressing clinical needs for eliminating intracellularly colonized bacteria. Here, we report the development of an integrated diagnostic-therapeutic microneedle patch incorporates the Res@PtZ-Z nanozyme hybrid. Res@PtZ-Z consists of a ZIF shell loaded with the natural compound resveratrol (Res), encapsulating a Pt-doped zinc oxide (ZnO) nanozyme core (PtZ). The Res component modulates charge distribution on the ZIF shell and attenuates bacterial virulence, thereby promoting the uptake of Res@PtZ-Z by host cells. The PtZ core, doped with Pt4+ to induce sublattice distortion in ZnO, exhibits oxidase-like, peroxidase-like, and catalase-like activities. Under intracellular hypoxic conditions, the cascade of these enzyme-like activities ensures a sustained generation of reactive oxygen species (ROS), enabling robust antibacterial effects. Additionally, Res@PtZ-Z enables real-time infection monitoring by oxidizing the 3,3',5,5'-tetramethylbenzidine (TMB) substrate to produce a distinct colorimetric response. This approach addresses both methicillin-resistant Staphylococcus aureus (MRSA) invasion and intracellular persistence, contributing to improved infection management and promoting wound healing.

Comprehensive analysis of the antibacterial activity of 5,8-dihydroxy-1,4-naphthoquinone derivatives against methicillin-resistant Staphylococcus aureus

Given the increasing concern regarding antibacterial resistance, the antimicrobial properties of naphthoquinones have recently attracted significant attention. While 1,4-naphthoquinone and its derivatives have been extensively studied, the antibacterial properties of 5,8-dihydroxy-1,4-naphthoquinone derivatives remain relatively unexplored. This study presents a comprehensive in vitro and in vivo analysis of the antibacterial activity of 35 naturally sourced and chemically synthesized derivatives of 5,8-dihydroxy-1,4-naphthoquinone. Kirby-Bauer antibiotic testing identified three compounds with activity against methicillin-resistant Staphylococcus aureus (MRSA), with one compound (PNP-02) demonstrating activity comparable to vancomycin in minimum inhibitory concentration, minimum bactericidal concentration (MBC), and time-kill assays. Microscopic and biochemical analyses revealed that PNP-02 adversely affects the cell wall and cell membrane of MRSA. Mechanistic investigations, including proteomic sequencing analyses, Western blotting, and RT-qPCR assays, indicated that PNP-02 compromises cell membrane integrity by inhibiting arginine biosynthesis and pyrimidine metabolism pathways, thereby increasing membrane permeability and inducing bacterial death. In an in vivo mouse model of skin wound healing, PNP-02 exhibited antibacterial efficacy similar to vancomycin. The compound demonstrated low toxicity to cultured human cells and in hemolysis assays and remained stable during serum incubation. These findings suggest that PNP-02 possesses promising bioactivity against MRSA and represents a potential novel antibacterial agent.

Antibacterial and anti-virulence activity of eco-friendly resveratrol-loaded lipid nanocapsules against methicillin-resistant staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is challenging modern antimicrobial therapy due to its high antimicrobial resistance. Nutraceuticals have gained a lot of interest and their incorporation into nanoparticles further improves their efficacy. This study aimed to evaluate the antibacterial activity of linalool-based lipid nanocapsules loaded with resveratrol (LIN-LNC-RES) as a synergistic strategy against MRSA. LIN-LNC-RES were prepared by the phase inversion temperature method and characterized for their colloidal properties, in vitro release, and stability. The antibacterial and antibiofilm activity against S. aureus and different MRSA clinical isolates were investigated. Furthermore, scanning electron microscopy (SEM) imaging for visualization of biofilm formation and bacterial membrane integrity as well as mechanistic investigation using quantitative real-time polymerase chain reaction (qRT-PCR) analysis were performed. LIN-LNCs-RES demonstrated favorable properties with a size of 35.19 ± 0.72 nm, PDI of 0.09 ± 0.02 and a zeta potential of -2.53 ± 0.07 mV with RES 98% EE. They showed a controlled release of RES over 24 h and were stable at 4 °C for 3 months. Compared to free drug, LIN-LNC-RES showed a 4-fold decrease in MIC values and 10-fold decrease in half maximal biofilm inhibitory concentration value. Biofilm eradication assay showed superiority of LIN-LNC-RES over RES against all isolates with disrupted bacterial membranes as revealed by SEM. Mechanistically, qRT-PCR showed that LIN-LNC-RES significantly reduced RNAIII gene expression as well as the expression of SaeRS two component system, potentially affecting quorum sensing and virulence factors expression. RES-loaded LIN-based nanosystem offers a great potential for combating MRSA infections, neutralizing its virulence activity hence, overcoming antimicrobial resistance.

Disarming Staphylococcus aureus: Review of Strategies Combating This Resilient Pathogen by Targeting Its Virulence

Staphylococcus aureus is a formidable pathogen notorious for its antibiotic resistance and diverse virulence mechanisms, including toxin production, biofilm formation, and immune evasion. This article explores innovative anti-virulence strategies to disarm S. aureus by targeting critical virulence factors without exerting bactericidal pressure. Key approaches include inhibiting adhesion and biofilm formation, neutralizing toxins, disrupting quorum sensing (e.g., Agr system inhibitors), and blocking iron acquisition pathways. Additionally, interventions targeting two-component regulatory systems are highlighted. While promising, challenges such as strain variability, biofilm resilience, pharmacokinetic limitations, and resistance evolution underscore the need for combination therapies and advanced formulations. Integrating anti-virulence strategies with traditional antibiotics and host-directed therapies offers a sustainable solution to combat multidrug-resistant S. aureus, particularly methicillin-resistant strains (MRSA), and mitigate the global public health crisis.

Bactericidal and anti-quorum sensing activity of repurposing drug Visomitin against Staphylococcus aureus

With the growing antibiotic resistance in Staphylococcus aureus, it is imperative to develop innovative therapeutic strategies against new targets to reduce selective survival pressures and incidence of resistance. In S. aureus, interbacterial communication relies on a quorum sensing system that regulates gene expression and physiological activities. Here, we identified that Visomitin, an antioxidant small molecule, exhibited bactericidal efficacy against methicillin-resistant S. aureus and its high tolerance phenotypes like intracellular bacteria and persister cells without inducing resistance. Critically, sub-minimal inhibitory concentrations (sub-MICs) of Visomitin could serve as a potent quorum-quencher reducing virulence production (such as haemolysin and staphyloxanthin), along with inhibiting biofilm formation, self-aggregation, and colony spreading of S. aureus. These effects were probably mediated by interfering with the S. aureus accessory gene regulator quorum sensing system. In summary, our findings suggest that Visomitin shows dual antimicrobial effects, including bactericidal effects at the concentrations above MIC and quorum sensing inhibition effects at sub-MICs, which holds promise for treating MRSA-related refractory infections.

Recent advances in the use of resveratrol against Staphylococcus aureus infections (Review)

As a notorious bacterial pathogen, Staphylococcus aureus (S. aureus) can readily induce infections in the community and hospital, causing significant morbidity and mortality. With the extensive rise of multiple resistance, conventional antibiotic therapy has rapidly become ineffective for related infections. Resveratrol is a naturally occurring polyphenolic substance that has been demonstrated to have effective antimicrobial activity against S. aureus. Resveratrol at sub-inhibitory doses can suppress the expression of virulence factors, contributing to attenuated biofilm formation, interference with quorum sensing and the inhibition of the production of toxins. As a promising efflux pump inhibitor, resveratrol enhances antibiotic susceptibility to a certain extent. In conjunction with conventional antibiotics, resveratrol displays unique synergistic effects with norfloxacin and aminoglycoside on S. aureus, yet antagonizes the lethal effects of daptomycin, oxacillin, moxifloxacin and levofloxacin. Nevertheless, given the low oral bioavailability of resveratrol, advanced formulations need to be developed to delay the rapid metabolism conversion to low or inactive conjugates. The present review discusses the antibacterial properties of resveratrol against S. aureus, in an aim to provide in-depth insight for researchers to address the challenges of antimicrobial resistance.

Antimicrobial efficiency and cytocompatibility of resveratrol and naringin as chemical decontaminants on SLA surface

Bacterial biofilms are the major etiology agent of peri-implant disease. Chemical decontamination is a promising treatment strategy against bacterial biofilms; however, its applications are limited by its low efficiency and poor biocompatibility. In contrast to three conventional cleaners (sterile saline, hydrogen peroxide, and chlorhexidine), this study used resveratrol and naringin solutions to remove mature Staphylococcus aureus and Porphyromonas gingivalis biofilm on sandblasted (with large grit and acid-etched (SLA) titanium surface. To determine changes in surface characteristics, the surface wettability and roughness were measured, and micromorphology was observed by scanning electron microscopy. With crystal violet (CV) and live/dead bacterial staining, residual plaque quantity and composition were measured. The biocompatibility was tested using pH and cytotoxicity, as well as by osteoblasts (MC3T3-E1) adhesion, proliferation, and differentiation, and fibroblasts (L-929) proliferation were also analyzed. It was found that resveratrol and naringin solutions were more effective in restoring surface characteristics and also showed that less plaque and viable bacteria were left. Naringin removed S. aureus biofilms better than chlorhexidine. Alkaline resveratrol and naringin solutions increased cell adhesion, proliferation, and osteogenic differentiation without any cytotoxicity. Resveratrol increased the expression of mRNA and protein associated with osteogenesis. In conclusion, resveratrol and naringin effectively restored SLA titanium surface characteristics and decontaminated the biofilm with good biocompatibility, suggesting their therapeutic potential as chemical decontaminants.

IMPORTANCE

Bacterial biofilms are considered the primary etiology of peri-implant disease. Physical cleaning is the most common way to remove bacterial biofilm, but it can cause grooving, melting, and deposition of chemicals that alter the surface of implants, which may hamper biocompatibility and re-osseointegration. Chemical decontamination is one of the most promising treatments but is limited by low efficiency and poor biocompatibility. Our study aims to develop safer, more effective chemical decontaminants for peri-implant disease prevention and treatment. We focus on resveratrol and naringin, two natural compounds, which have shown to be more effective in decontaminating biofilms on dental implant surfaces and exerting better biocompatibility. This research is groundbreaking as it is the first exploration of natural plant extracts' impact on mature bacterial biofilms on rough titanium surfaces. By advancing this knowledge, we seek to contribute to more effective and biocompatible strategies for combating peri-implant diseases, enhancing oral health, and prolonging implant lifespan.

Hla protein expression and artesunate prevented mice from further damage caused by Staphylococcus aureus pneumonia

The laboratory standard MRSA strain WHO-2 and clinical isolate S1 were used to establish a pneumonia infection model. The results showed that methicillin increased the expression of Hla and PVL protein at subminimum inhibitory concentration, while artesunate decreased the secretion of Hla and PVL protein. Artesunate alone reduced hemolysin expression and reversed methicillin-induced increases in Hla and PVL proteins. In addition, the study found that the combination of artesunate and methicillin had the best therapeutic effect, with survival rates of 70 % and 40 % at seven days, respectively (corresponding to the WHO-2 and S1 strains). The combination treatment was able to reduce cell mortality, showing a 65 % and 46 % reduction in cell mortality, respectively. The study also found that the combination therapy decreased the expression of alpha-hemolysin and pantone valentin leukin in the culture medium and significantly reduced the activation of NF-kB. This is caused by a significant decrease in the expression of inflammatory factors.

The role of male hormones in bacterial infections: enhancing Staphylococcus aureus virulence through testosterone-induced Agr activation

Staphylococcus aureus is a notorious pathogen predominantly involved in skin and soft tissue infections, exhibiting a distinct innate sex bias. This study explores the influence of testosterone on the virulence of S. aureus and elucidates its underlying mechanisms. Utilizing a skin abscess model in intact and castrated male mice, we assessed the effects of testosterone on S. aureus pathogenicity. Compared to controls, castrated mice showed significantly reduced abscess sizes and decreased bacterial loads, highlighting the role of testosterone in modulating the severity of S. aureus infections. In vitro experiments revealed that testosterone enhances the hemolytic activity, cytotoxicity, and oxidative stress resistance of S. aureus. Real-time quantitative PCR analysis showed a significant upregulation of the genes encoding α-hemolysin (hla) and phenol-soluble modulin (psmα). Importantly, testosterone treatment significantly enhanced the expression of the accessory gene regulator (Agr) quorum-sensing system components (agrC, agrA, agrB, agrD), while the SaeRS system (saeR, saeS, and sbi) exhibited only slight changes. Gene knockout experiments revealed that deletion of agrC, rather than saeRS and agrBD, abolishes the testosterone-induced enhancement of hemolysis and gene expression, underscoring the key role of AgrC. Molecular docking simulations indicated a direct interaction between testosterone and AgrC protein, with a strong binding affinity at the active site residue SER201. This study provides new insights into the mechanistic basis of how testosterone enhances the pathogenicity of S. aureus, potentially contributing to increased male susceptibility to S. aureus infections and offering a targeted approach for therapeutic interventions.

Elucidating the potential of isorhapontigenin in targeting the MgrA regulatory network: a paradigm shift for attenuating MRSA virulence

As methicillin-resistant Staphylococcus aureus (MRSA) exhibits formidable resistance to many drugs, the imperative for alternative therapeutic strategies becomes increasingly evident. At the heart of our study is the identification of a novel inhibitor through fluorescence anisotropy assays, specifically targeting the crucial multiple gene regulator A (MgrA) regulatory network in S. aureus. Isorhapontigenin (Iso), a natural compound, exhibits outstanding inhibitory efficacy, modulating bacterial virulence pathways without exerting direct bactericidal activity. This suggests a paradigm shift toward attenuating virulence instead of purely focusing on bacterial elimination. Through comprehensive in vitro and in vivo evaluations, we elucidated the complex interplay between Iso and MgrA, leading to reduced S. aureus adhesion, and overall virulence. At the cellular level, Iso offers significant protection to A549 cells infected with S. aureus, reducing cellular damage. Importantly, Iso augments the chemotaxis of neutrophils, curtailing the immune evasion capabilities of S. aureus. Furthermore, in vivo investigations highlight the notable effectiveness of Iso against MRSA-induced pneumonia and within the Galleria mellonella infection model, underscoring its pivotal role in the evolving realm of antibacterial drug discovery. Significantly, when Iso is used in combination with vancomycin, it outperforms its solo application, indicating a more pronounced therapeutic impact. This seminal research emphasizes Iso's potential as a primary defense against the surge of multidrug-resistant pathogens, heralding new prospects in antimicrobial therapy.

Exploring the potential of isorhapontigenin: attenuating Staphylococcus aureus virulence through MgrA-mediated regulation

The emerging prevalence of drug-resistant Staphylococcus aureus isolates underscores the urgent need for alternative therapeutic strategies due to the declining effectiveness of traditional antibiotics in clinical settings. MgrA, a key virulence regulator in S. aureus, orchestrates the expression of numerous virulence factors. Here, we report the discovery of isorhapontigenin, a methoxylated analog of resveratrol, as a potential anti-virulence agent against S. aureus. Isorhapontigenin effectively inhibits the hemolytic activity of S. aureus in a non-bactericidal manner. Additionally, it significantly reduces the cytotoxicity of S. aureus and impairs its ability to survive in macrophages. Mechanistically, isorhapontigenin modulates the expression of virulence factors, dose-dependently downregulating hla and upregulating the MgrA-regulated gene spa. Electrophoretic mobility shift assays demonstrated that isorhapontigenin inhibits the binding of MgrA to the hla promoter in a dose-dependent manner. Thermal shift assays confirmed the direct interaction between isorhapontigenin and the MgrA protein. The in vivo experiments demonstrated that isorhapontigenin significantly reduced the area of skin abscesses and improved survival in a pneumonia model while decreasing bacterial burden and inflammation in the lungs. In conclusion, isorhapontigenin holds potential as a candidate drug for further development as an anti-virulence agent for treating S. aureus infections.

IMPORTANCE

The emergence of antibiotic-resistant Staphylococcus aureus strains presents a formidable challenge to public health, necessitating novel approaches in combating these pathogens. Traditional antibiotics are becoming increasingly ineffective, leading to a pressing need for innovative therapeutic strategies. In this study, targeting virulence factors that play a crucial role in the pathogenesis of bacterial infections offers a promising alternative to circumvent resistance mechanisms. The discovery of isorhapontigenin as an inhibitor of S. aureus virulence represents a significant advance in anti-virulence therapy.

Staphylococcus aureus biofilm: Formulation, regulatory, and emerging natural products-derived therapeutics

Staphylococcus aureus can readily form biofilm which enhances the drug-resistance, resulting in life-threatening infections involving different organs. Biofilm formation occurs due to a series of developmental events including bacterial adhesion, aggregation, biofilm maturation, and dispersion, which are controlled by multiple regulatory systems. Rapidly increasing research and development outcomes on natural products targeting S. aureus biofilm formation and/or regulation led to an emergent application of active phytochemicals and combinations. This review aimed at providing an in-depth understanding of biofilm formation and regulation mechanisms for S. aureus, outlining the most important antibiofilm strategies and potential targets of natural products, and summarizing the latest progress in combating S. aureus biofilm with plant-derived natural products. These findings provided further evidence for novel antibiofilm drugs research and clinical therapies.

Progress of Antimicrobial Mechanisms of Stilbenoids

Antimicrobial drugs have made outstanding contributions to the treatment of pathogenic infections. However, the emergence of drug resistance continues to be a major threat to human health in recent years, and therefore, the search for novel antimicrobial drugs is particularly urgent. With a deeper understanding of microbial habits and drug resistance mechanisms, various creative strategies for the development of novel antibiotics have been proposed. Stilbenoids, characterized by a C6-C2-C6 carbon skeleton, have recently been widely recognized for their flexible antimicrobial roles. Here, we comprehensively summarize the mode of action of stilbenoids from the viewpoint of their direct antimicrobial properties, antibiofilm and antivirulence activities and their role in reversing drug resistance. This review will provide an important reference for the future development and research into the mechanisms of stilbenoids as antimicrobial agents.

Inhibitory effects of citral on the production of virulence factors in Staphylococcus aureus and its potential application in meat preservation

Foodborne diseases caused by Staphylococcus aureus contamination on meat and meat products has gained increasing attention in recent years, while the pathogenicity of S. aureus is mainly attributed to its virulence factors production, which is primarily regulated by quorum sensing (QS) system. Herein, we aimed to uncover the inhibitory effects and mechanisms of citral (CIT) on virulence factors production by S. aureus, and further explore its potential application in pork preservation. Susceptibility test confirmed the antibacterial properties of CIT against S. aureus, the minimal inhibitory concentration (MIC) was 0.25 mg/mL. Treatment with sub-MICs of CIT reduced the hemolytic activity by inhibiting the production of α-hemolysin, and staphylococcal enterotoxins (SEs) production was significantly inhibited by CIT in both culture medium and pork without affecting bacterial growth. Transcriptomic analysis indicated that the differentially expression genes encoding α-hemolysin, SEs, and other virulence factors were down-regulated after treatment with 1/2MIC CIT. Moreover, the genes related to QS including agrA and agrC were also down-regulated, while the global transcriptional regulator sarA was up-regulated. Data here demonstrated that CIT could inhibited S. aureus virulence factors production through disturbing QS systems. In a challenge test, the addition of CIT caused a remarkable inhibition of S. aureus population and delay in lipid oxidation and color change on pork after 15 days incubation at 4 °C. These findings demonstrated that CIT could not only efficiently restrain the production of S. aureus virulence factors by disturbing QS, but also exhibit the potential application on the preservation of meat products.

Effect of Resveratrol and Curcumin on Gene Expression of Methicillin-Resistant Staphylococcus aureus (MRSA) Toxins

Staphylococcus aureus is an opportunistic pathogen that can lead to a number of potentially terrible community- and hospital-acquired illnesses. Among the diverse set of virulence factors that S. aureus possesses, secreted toxins play a particularly preeminent role in defining its virulence. In this work, we aimed to facilitate the development of novel strategies utilizing natural compounds to lower S. aureus's toxin production and consequently enhance therapeutic approaches. Two natural polyphenols, resveratrol (RSV) and curcumin (CUR), were tested for their effect on reducing toxin gene production of MRSA isolates. Fifty clinical MRSA isolates were gathered from Riyadh and Jeddah. Molecular screening of toxin genes (sea, seb, sec, sed, seh, lukF, and lukS) harbored by MRSA was performed. Sub-inhibitory concentrations of RSV (50 μg/ml) and CUR (20 μg/ml) were determined to study their effect on the gene expression MRSA's toxin genes. Our findings revealed the presence of the tested genes in MRSA isolates, with lukF being the most prevalent gene and seh the least detected gene. We found that RSV reduced the relative expression of toxin genes, sea, seb, lukF, and lukS, respectively, while CUR decreased the relative expression of sea and seb genes in the examined isolates. Regarding lukF and lukS, CUR downregulated the expression of both genes in some isolates and upregulated the expression in other isolates. From these results, we concluded that RSV and CUR could be used as alternative therapeutic approaches to treat MRSA infections through reducing toxin production.

Development of a dual fluorescent reporter system to identify inhibitors of Staphylococcus aureus virulence factors

IMPORTANCE

Staphylococcus aureus is a formidable pathogen responsible for a wide range of infections, and the emergence of antibiotic-resistant strains has posed significant challenges in treating these infections. In this study, we have established a novel dual reporter system capable of concurrently monitoring the activities of two critical virulence regulators in S. aureus. By incorporating both reporters into a single screening platform, we provide a time- and cost-efficient approach for assessing the activity of compounds against two distinct targets in a single screening round. This innovative dual reporter system presents a promising strategy for the identification of molecules capable of modulating virulence gene expression in S. aureus, potentially expediting the development of antivirulence therapies.

Draft genome sequence of Staphylococcus aureus sequence type 5 SA01 isolated from bloodstream infection and comparative analysis with reference strains

A Staphylococcus aureus isolate (SA01) obtained from bloodstream infection exhibited a remarkable drug resistance profile. In this study, we report the draft genome sequence of S. aureus ST 5 SA01, a multidrug-resistant isolate, and analyzed the genes associated with drug resistance and virulence. The genome sketch of S. aureus ST5 SA01 was sequenced with Illumina and annotated using the Prokka software. Rapid Annotation Subsystem Technology (RAST) was used to verify the gene functions in the genome subsystems. The Comprehensive Antibiotic Resistance Database (CARD) and Virulence Factor Database (VFDB) were used in the analysis. The RAST indicated a contribution of 25 proteins to host adenine, fibronectin-binding protein A (FnbA), and biofilm formation as an intercellular polysaccharide adhesive system (PIA). The MLST indicated that S. aureus ST 5 SA01 belongs to ST5 (CC5). In silico analyses also showed an extensive repertoire of genes associated with toxins, such as LukGH leukocidin, enterotoxins, and superantigen staphylococcal classes (SSL). The 11 genes for antimicrobial resistance in S. aureus ST 5 SA01 showed similarity and identity above ≥ 99% with nucleotide sequences deposited in GenBank. Although studies on ST5 clones in Brazil are scarce, monitoring the clone of S. aureus ST 5 SA01 is essential, as it has become a problem in pediatrics in several countries.

Flavone inhibits Staphylococcus aureus virulence via inhibiting the sae two component system

The rising prevalence of antibiotic resistance in Staphylococcus aureus calls for the development of innovative antimicrobial agents targeting novel pathways. S. aureus generates various virulence factors that compromise host defense mechanisms. Flavone, a core structure of flavonoids, has been shown to diminish the production of staphyloxanthin and alpha-hemolysin. Nonetheless, the influence of flavone on the majority of other virulence factors in S. aureus and its underlying molecular mechanism remain elusive. In this study, we examined the impact of flavone on the transcriptional profile of S. aureus using transcriptome sequencing. Our findings revealed that flavone substantially downregulated the expression of over 30 virulence factors implicated in immune evasion by the pathogen. Gene set enrichment analysis of the fold change-ranked gene list in relation to the Sae regulon indicated a robust association between flavone-induced downregulation and membership in the Sae regulon. Through the analysis of Sae target promoter-gfp fusion expression patterns, we observed a dose-dependent inhibition of Sae target promoter activity by flavone. Moreover, we discovered that flavone protected human neutrophils from S. aureus-mediated killing. Flavone also decreased the expression of alpha-hemolysin and other hemolytic toxins, resulting in a reduction in S. aureus' hemolytic capacity. Additionally, our data suggested that the inhibitory effect of flavone on the Sae system operates independently of its capacity to lower staphyloxanthin levels. In conclusion, our study proposes that flavone exhibits a broad inhibitory action on multiple virulence factors of S. aureus by targeting the Sae system, consequently diminishing the bacterium's pathogenicity.

The natural product, echinatin, protects mice from methicillin-resistant Staphylococcus aureus pneumonia by inhibition of alpha-hemolysin expression

Antimicrobial resistance (AMR) is a global, multifaceted crisis that poses significant challenges to the successful eradication of devastating pathogens, particularly methicillin-resistant Staphylococcus aureus (MRSA), a persistent superbug that causes devastating infections. The scarcity of new antibacterial drugs is obvious, and antivirulence strategies that reduce the pathogenicity of bacteria by weakening their virulence have become the subject of intense investigation. Alpha-hemolysin (Hla), a cytolytic pore-forming toxin, has a pivotal role in S. aureus pathogenesis. Here, we demonstrated that echinatin, a natural compound isolated from licorice, effectively inhibited the hemolytic activity of MRSA at 32 μg/mL. In addition, echinatin did not interfere with bacterial growth and had no significant cytotoxicity at the inhibitory concentration of S. aureus hemolysis. Heptamer formation tightly correlated with Hla-mediated cell invasion, whereas echinatin did not affect deoxycholic acid-induced oligomerization of Hla. Echinatin affected hemolytic activity through indirect binding to Hla as confirmed by the neutralization assay and cellular thermal shift assay (CETSA). Furthermore, qRT-PCR and western blot analyses revealed that echinatin suppressed Hla expression at both the mRNA and protein levels as well as the transcript levels of Agr quorum-sensing system-related genes. Additionally, when echinatin was added to a coculture system of A549 cells and S. aureus, it significantly reduced cell damage. Importantly, echinatin exhibited a significant therapeutic effect in an MRSA-induced mouse pneumonia model. In conclusion, the present findings demonstrated that echinatin significantly inhibits the hemolysin effect and may be a potential candidate compound for combating drug-resistant MRSA infections.

Effect of povidone-iodine and propanol-based mecetronium ethyl sulphate on antimicrobial resistance and virulence in Staphylococcus aureus

Background

Reports are available on cross-resistance between antibiotics and biocides. We evaluated the effect of povidone-iodine (PVP-I) and propanol-based mecetronium ethyl sulphate (PBM) on resistance development, antibiotics cross-resistance, and virulence in Staphylococcus aureus.

Methods

The minimum inhibitory concentration (MIC) of PVP-I and PBM were determined against S. aureus ATCC 25923 using the agar-dilution method. Staphylococcus aureus ATCC 25923 was subjected to subinhibitory concentrations of the tested biocides in ten consecutive passages followed by five passages in a biocide-free medium; MIC was determined after each passage and after the fifth passage in the biocide-free medium. The developed resistant mutant was tested for cross-resistance to different antibiotics using Kirby-Bauer disk diffusion method. Antibiotic susceptibility profiles as well as biocides’ MIC were determined for 97 clinical S. aureus isolates. Isolates were categorized into susceptible and resistant to the tested biocides based on MIC distribution pattern. The virulence of the biocide-resistant mutant and the effect of subinhibitory concentrations of biocides on virulence (biofilm formation, hemolysin activity, and expression of virulence-related genes) were tested.

Results

PVP-I and PBM MIC were 5000 μg/mL and 664 μg/mL. No resistance developed to PVP-I but a 128-fold increase in PBM MIC was recorded, by repeated exposure. The developed PBM-resistant mutant acquired resistance to penicillin, cefoxitin, and ciprofloxacin. No clinical isolates were PVP-I-resistant while 48.5% were PBM-resistant. PBM-resistant isolates were more significantly detected among multidrug-resistant isolates. PVP-I subinhibitory concentrations (¼ and ½ of MIC) completely inhibited biofilm formation and significantly reduced hemolysin activity (7% and 0.28%, respectively). However, subinhibitory concentrations of PBM caused moderate reduction in biofilm activity and non-significant reduction in hemolysin activity. The ½ MIC of PVP-I significantly reduced the expression of hla, ebps, eno, fib, icaA, and icaD genes. The virulence of the biocide-resistant mutant was similar to that of parent strain.

Conclusion

PVP-I is a highly recommended antiseptic for use in healthcare settings to control the evolution of high-risk clones. Exposure to PVP-I causes no resistance-development risk in S. aureus, with virulence inhibition by subinhibitory concentrations. Also, special protocols need to be followed during PBM use in hospitals to avoid the selection of resistant strains.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13756-022-01178-9.

Small-molecule compound SYG-180-2-2 attenuates Staphylococcus aureus virulence by inhibiting hemolysin and staphyloxanthin production

Multi-drug resistant Staphylococcus aureus infection is still a serious threat to global health. Therefore, there is an urgent need to develop new antibacterial agents based on virulence factor therapy to overcome drug resistance. Previously, we synthesized SYG-180-2-2 (C21H16N2OSe), an effective small molecule compound against biofilm. The aim of this study was to investigate the anti-virulence efficacy of SYG-180-2-2 against Staphylococcus aureus. MIC results demonstrated no apparent antibacterial activity of the SYG-180-2-2. The growth curve assay showed that SYG-180-2-2 had nonlethal effect on S. aureus. Besides, SYG-180-2-2 strongly inhibited the hemolytic activity and staphyloxanthin synthesis in S. aureus. Inhibition of staphyloxanthin by SYG-180-2-2 enhanced the sensitivity of S. aureus to oxidants and human whole blood. In addition, SYG-180-2-2 significantly decreased the expression of saeR-mediated hemolytic gene hlb and staphyloxanthin-related crtM, crtN and sigB genes by quantitative polymerase chain reaction (qPCR). Meanwhile, the expression of oxidative stress-related genes sodA, sodM and katA also decreased. Galleria Mellonella assay revealed that SYG-180-2-2 was not toxic to larvae. Further, the larvae infection model showed that the virulence of bacteria was significantly reduced after 4 μg/mL SYG-180-2-2 treatment. SYG-180-2-2 also reduced skin abscess formation in mice by reducing bacterial burden and subcutaneous inflammation. In conclusion, SYG-180-2-2 might be a promising agent to attenuate the virulence of S. aureus by targeting genes associated with hemolytic activity and staphyloxanthin synthesis.

2,3-Dehydrokievitone combats methicillin-resistant Staphylococcus aureus infection by reducing alpha-hemolysin expression

Due to powerful drug resistance and fatal toxicity of methicillin-resistant Staphylococcus aureus (MRSA), therapeutic strategies against virulence factors present obvious advantages since no evolutionary pressure will induce bacterial resistance. Alpha-hemolysin (Hla) is an extracellular toxin secreted by Staphylococcus aureus and contributes to bacterial pathogenicity. Herein, we identified a natural product 2,3-dehydrokievitone (2,3-DHKV) for inhibiting Hla activity of MRSA strain USA300 but not affecting bacteria growth. 2,3-DHKV significantly decreased hemolysin expression in a dose-dependent manner, but it did not potently neutralize hemolysin activity. Subsequently, cellular thermal shift and heptamer formation assays confirmed that 2,3-DHK affects hemolytic activity through indirect binding to Hla. RT-qPCR and western blot revealed that 2,3-DHKV suppressed Hla expression at the mRNA and protein levels, and further decreased accessory gene regulator A (agrA) transcription levels. We also observed that 2,3-DHK significantly attenuated the damage of A549 cells by S. aureus and reduced the release of lactate dehydrogenase (LDH). Moreover, in the MRSA-induced pneumonia mouse model, 2,3-DHK treatment prolonged the life span of mice and reduced the bacterial load in the lungs, which significantly alleviated the damage to the lungs. In summary, this study proved that 2,3-DHK as a Hla inhibitor is a potential antivirulence agent against MRSA infection.

Synergistic antibacterial and anti-biofilm activities of resveratrol and polymyxin B against multidrug-resistant Pseudomonas aeruginosa

Bacterial infection caused by multidrug-resistant Pseudomonas aeruginosa has become a challenge in clinical practice. Polymyxins are used as the last resort agent for otherwise untreatable Gram-negative bacteria, including multidrug-resistant P.aeruginosa. However, pharmacodynamic (PD) and pharmacokinetic (PK) data on polymyxins suggest that polymyxin monotherapy is unlikely to generate reliably efficacious plasma concentrations. Also, polymyxin resistance has been frequently reported, especially among multidrug-resistant P.aeruginosa, which further limits its clinical use. A strategy for improving the antibacterial activity of polymyxins and preventing the development of polymyxin resistance is to use polymyxins in combination with other agents. In this study, we have demonstrated that resveratrol, a well tolerated compound, has synergistic effects when tested in vitro with polymyxin B on antibacterial and anti-biofilm activities. However, its' systemic use is limited as the required high plasma levels of resveratrol are not achievable. This suggests that it could be a partner for the combination therapy of polymyxin B in the treatment of topical bacterial infection caused by MDR P.aeruginosa.

Synergistic Antibacterial Activity with Conventional Antibiotics and Mechanism of Action of Shikonin against Methicillin-Resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is a troublesome pathogen that poses a global threat to public health. Shikonin (SKN) isolated from Lithospermum erythrorhizon (L. erythrorhizon) possesses a variety of biological activities. This study aims to explore the effect of the combined application of SKN and traditional antibiotics on the vitality of MRSA and the inherent antibacterial mechanism of SKN. The synergies between SKN and antibiotics against MRSA and its clinical strain have been demonstrated by the checkerboard assay and the time-kill assay. The effect of SKN on disrupting the integrity and permeability of bacterial cell membranes was verified by a nucleotide and protein leakage assay and a bacteriolysis assay. As determined by crystal violet staining, SKN inhibited the biofilm formation of clinical MRSA strains. The results of Western blot and qRT-PCR showed that SKN could inhibit the expression of proteins and genes related to drug resistance and S. aureus exotoxins. SKN inhibited the ability of RAW264.7 cells to release the pro-inflammatory cytokines TNF-α and IL-6, as measured by ELISA. Our findings suggest that SKN has the potential to be developed as a promising alternative for the treatment of MRSA infections.

Anti-virulence therapeutic strategies against bacterial infections: recent advances

The emergence and increasing prevalence of multidrug-resistant pathogens has become a major global healthcare problem. According to the World Health Organization if these trends continue, mortality from infection in 2050 will be higher than that from cancer. Microorganisms have various resistance mechanisms against different classes of antibiotics that emphasize the need for discovery of new antimicrobial compounds to treat bacterial infections. An interesting and new strategy for disarming pathogens is antivirulence therapy by blocking bacterial virulence factors or pathogenicity. Therefore, the use of these new pathoblockers could reduce the administration of broad-spectrum antimicrobials and prevalence of resistant strains. This review provides an overview of the antivirulence strategies published studies between years 2017 and 2021. Most antivirulence strategies focused on adhesins, toxins and bacterial communication. Additionally, targeting two-component systems and ncRNA elements were also examined in some studies. These new strategies have the potential to replace traditional antimicrobial agents and can be used to treat infections, especially infections caused by resistant pathogens, by targeting virulence factors.

Strategically designed SPEEK nanofibrous scaffold with tailored delivery ofresveratrolfor skin wound regeneration

Electro-spinnable polymeric materials can easily form two-dimensional (2D) nanofibrous scaffolds improving biochemical functionalities specially in the area of skin wound healing and nanomedicine, but it has been hard to achieve this on a highly mechanically stable biopolymer, Poly ether ether ketone (PEEK), due to its intrinsic hydrophobicity and chemical inertness. Herein, we demonstrated a novel nanomedicine healing system consisting of sulphonated poly ether ether ketone combined withresveratrol(SPEEK+RSV), which could act as an effective 2D nano bio-materialin vitroandin vivo, without observable cytotoxicity. The fabricated nanocomposites exhibited enriched skin cell proliferation and adhesion as confirmed from the results of MTT, cell adhesion and live-dead assay. Results of SEM analysis showed a uniform nano-sized distribution with adequate pore size and porosity % facilitating a desired breathable environment at the wound site. The results of FT-IR, tensile studies and TGA analyses confirmed the presence of appropriate bonds and improved mechanical stability of theRSVincorporated nanofibrous scaffold. Results of anti-microbial analysis portrayed good potentiality of the fabricated nanofibers in treating wounds colonized with bacterial infections. Controlled drug release of resveratrol established the bio-compatibility of the nanofibers in skin wound regeneration.In vivoanalysis assessed in female Wistar rats enabled complete wound closure with 100 % wound contraction within 16 days. Results of histopathology analysis through H-E and MT staining presented the re-surfing of the wound environment with regeneration of epithelium, granulation tissue and collagen. Thus, the fabricated 2D nanofibrous scaffold incorporated with pharmaceutical RSV bio-medicine perceptively mimicked skin ECM convincingly aiding the progression of skin wound regeneration mechanism.

NWMN2330 May Be Associated with the Virulence of Staphylococcus aureus by Increasing the Expression of hla and saeRS

Introduction

Staphylococcus aureus is an opportunistic pathogen that can cause life-threatening bloodstream infections such as sepsis and endocarditis. In recent years, the emergence and increase of methicillin-resistant and multidrug-resistant S. aureus has posed a great challenge to the antibiotic treatment of infectious diseases. Anti-virulence strategies targeting virulence factors are an effective new therapy for the treatment of S. aureus infections.

Results

In this study, we constructed a NWMN2330 deletion mutant (Newman-ΔNWMN2330) and a complement (Newman-ΔNWMN2330-C) of S. aureus Newman to study the role of NWMN2330 in the virulence of S. aureus. Through transcriptome sequencing, it was found that the expression of 224 genes in Newman-ΔNWMN2330 was significantly different (>2-fold) compared with S. aureus Newman, and these differentially expressed genes were related to multiple functions of S. aureus. And we found that NWMN2330 could positively regulate the expression of S. aureus hla gene. Therefore, the deletion mutant Newman-ΔNWMN2330 exhibited lower hemolytic activity and lower α-toxin production than Newman. Newman-ΔNWMN2330 also exhibited lower lethality and pathogenicity in worm survival experiments and nude mouse skin abscess model. RT-qPCR results showed that compared with the wild-type strain, the expression of saeRS and hla in Newman-ΔNWMN2330 strain was significantly reduced at the mRNA level, which preliminarily indicated that NWMN2330 promoted the expression of hla by up-regulating saeRS.

Discussion

In general, our results indicated that NWMN2330 may be associated with the virulence of Staphylococcus aureus by increasing the expression of hla and saeRS.

Two Novel Phenylpropanoid Trimers From Ligusticum chuanxiong Hort With Inhibitory Activities on Alpha-Hemolysin Secreted by Staphylococcus aureus

The emergence of antibiotic resistance in Staphylococcus aureus has necessitated the development of innovative anti-infective agents acting on novel targets. Alpha-hemolysin (Hla), a key virulence factor of S. aureus, is known to cause various cell damage and death. In this study, with bioassay-guided fractionation, a pair of unusual epimeric lignan trimers, ligustchuanes A and B (1 and 2), were isolated from the rhizomes of Ligusticum chuanxiong Hort, together with two known phthalides being identified by UPLC-QTOF-MS. To the best of our knowledge, trimers with rare C8-C9″-type neolignan and ferulic acid fragments have not been identified in any natural product. Both of them were isolated as racemic mixtures, and their absolute configurations were determined by comparing experimental and calculated ECD spectra after enantioseparation. Ligustchuane B exhibited an outstanding inhibitory effect on α-hemolysin expression in both MRSA USA300 LAC and MSSA Newman strains at concentrations of 3 and 6 μM, respectively. Notably, a mouse model of infection further demonstrated that ligustchuane B could attenuate MRSA virulence in vivo.

Control of Foodborne Staphylococcus aureus by Shikonin, a Natural Extract

Foodborne Staphylococcus aureus (S. aureus) has attracted widespread attention due to its foodborne infection and food poisoning in human. Shikonin exhibits antibacterial activity against a variety of microorganisms, but there are few studies on its antibacterial activity against S. aureus. This study aims to explore the antibacterial activity and mechanism of shikonin against foodborne S. aureus. The results show that the minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) of shikonin were equal for all tested strains ranging from 35 μg/mL to 70 μg/mL. Shikonin inhibited the growth of S. aureus by reducing intracellular ATP concentrations, hyperpolarizing cell membrane, destroying the integrity of cell membrane, and changing cell morphology. At the non-inhibitory concentrations (NICs), shikonin significantly inhibited biofilm formation of S. aureus, which was attributed to inhibiting the expression of cidA and sarA genes. Moreover, shikonin also markedly inhibited the transcription and expression of virulence genes (sea and hla) in S. aureus. In addition, shikonin has exhibited antibacterial ability against both planktonic and biofilm forms of S. aureus. Importantly, in vivo results show that shikonin has excellent biocompatibility. Moreover, both the heat stability of shikonin and the antimicrobial activity of shikonin against S. aureus were excellent in food. Our findings suggest that shikonin are promising for use as a natural food additive, and it also has great potential in effectively controlling the contamination of S. aureus in food and reducing the number of illnesses associated with S. aureus.

Isovitexin Is a Direct Inhibitor of Staphylococcus aureus Coagulase

Staphylococcus aureus (S. aureus) is a major pathogen that causes human pneumonia, leading to significant morbidity and mortality. S. aureus coagulase (Coa) triggers the polymerization of fibrin by activating host prothrombin, which then converts fibrinogen to fibrin and contributes to S. aureus pathogenesis and persistent infection. In our research, we demonstrate that isovitexin, an active traditional Chinese medicine component, can inhibit the coagulase activity of Coa but does not interfere with the growth of S. aureus. Furthermore, we show through thermal shift and fluorescence quenching assays that isovitexin directly binds to Coa. Dynamic simulation and structure-activity relationship analyses suggest that V191 and P268 are key amino acid residues responsible for the binding of isovitexin to Coa. Taken together, these data indicate that isovitexin is a direct Coa inhibitor and a promising candidate for drug development against S. aureus infection.

Influence of sub-inhibitory concentrations of antimicrobials on micrococcal nuclease and biofilm formation in Staphylococcus aureus

A major contributor to biomaterial associated infection (BAI) is Staphylococcus aureus. This pathogen produces a protective biofilm, making eradication difficult. Biofilms are composed of bacteria encapsulated in a matrix of extracellular polymeric substances (EPS) comprising polysaccharides, proteins and extracellular DNA (eDNA). S. aureus also produces micrococcal nuclease (MN), an endonuclease which contributes to biofilm composition and dispersion, mainly expressed by nuc1. MN expression can be modulated by sub-minimum inhibitory concentrations of antimicrobials. We investigated the relation between the biofilm and MN expression and the impact of the application of antimicrobial pressure on this relation. Planktonic and biofilm cultures of three S. aureus strains, including a nuc1 deficient strain, were cultured under antimicrobial pressure. Results do not confirm earlier findings that MN directly influences total biomass of the biofilm but indicated that nuc1 deletion stimulates the polysaccharide production per CFU in the biofilm in in vitro biofilms. Though antimicrobial pressure of certain antibiotics resulted in significantly increased quantities of polysaccharides per CFU, this did not coincide with significantly reduced MN activity. Erythromycin and resveratrol significantly reduced MN production per CFU but did not affect total biomass or biomass/CFU. Reduction of MN production may assist in the eradication of biofilms by the host immune system in clinical situations.

Antibacterial and Anti-biofilm Efficacy of Chinese Dragon's Blood Against Staphylococcus aureus Isolated From Infected Wounds

Chinese dragon’s blood (CDB), a characteristic red resin, is an important traditional Chinese medicine (TCM), and empiric therapy of infected wounds with CDB is performed in clinical settings. For the first time, we herein report the antibacterial and anti-biofilm efficacy of CDB against Staphylococcus aureus (S. aureus). Antimicrobial susceptibility testing, growth curve assay, time-kill curve assay, crystal violet biofilm assay, scanning electron microscope (SEM) analysis, cell membrane tests, and quantitative real-time polymerase chain reaction (qRT-PCR) were used for this purpose. The results suggested that the minimum inhibitory concentration (MIC) values of CDB against S. aureus ranged from 32 to 128 μg/mL. Growth curves and time-kill curves confirmed that CDB could inhibit the growth of S. aureus. The biofilm formation ability and the expression levels of saeR, saeS, and hla of S. aureus in the presence and absence of CDB were statistically significant (P < 0.01). The results of SEM analysis and cell membrane tests revealed that exposure to CDB had some destructive effects on S. aureus cells. In conclusion, CDB exhibits positive antibacterial activity against S. aureus. Moreover, CDB could reduce the biofilm formation and the virulence factors of S. aureus by downregulating the expression levels of saeR, saeS, and hla genes. These findings indicated that CDB has immense potential to serve as a viable alternative for the treatment of infected wounds caused by S. aureus in clinical settings.

The Use of Micro- and Nanocarriers for Resveratrol Delivery into and across the Skin in Different Skin Diseases-A Literature Review

In recent years, polyphenols have been extensively studied due to their antioxidant, anticancer, and anti-inflammatory properties. It has been shown that anthocyanins, flavonols, and flavan-3-ols play an important role in the prevention of bacterial infections, as well as vascular or skin diseases. Particularly, resveratrol, as a multi-potent agent, may prevent or mitigate the effects of oxidative stress. As the largest organ of the human body, skin is an extremely desirable target for the possible delivery of active substances. The transdermal route of administration of active compounds shows many advantages, including avoidance of gastrointestinal irritation and the first-pass effect. Moreover, it is non-invasive and can be self-administered. However, this delivery is limited, mainly due to the need to overpassing the stratum corneum, the possible decomposition of the substances in contact with the skin surface or in the deeper layers thereof. In addition, using resveratrol for topical and transdermal delivery faces the problems of its low solubility and poor stability. To overcome this, novel systems of delivery are being developed for the effective transport of resveratrol across the skin. Carriers in the micro and nano size were demonstrated to be more efficient for safe and faster topical and transdermal delivery of active substances. The present review aimed to discuss the role of resveratrol in the treatment of skin abnormalities with a special emphasis on technologies enhancing transdermal delivery of resveratrol.

Plant Derived Natural Products against Pseudomonas aeruginosa and Staphylococcus aureus: Antibiofilm Activity and Molecular Mechanisms

Bacteria are social organisms able to build complex structures, such as biofilms, that are highly organized surface-associated communities of microorganisms, encased within a self- produced extracellular matrix. Biofilm is commonly associated with many health problems since its formation increases resistance to antibiotics and antimicrobial agents, as in the case of Pseudomonas aeruginosa and Staphylococcus aureus, two human pathogens causing major concern. P. aeruginosa is responsible for severe nosocomial infections, the most frequent of which is ventilator-associated pneumonia, while S. aureus causes several problems, like skin infections, septic arthritis, and endocarditis, to name just a few. Literature data suggest that natural products from plants, bacteria, fungi, and marine organisms have proven to be effective as anti-biofilm agents, inhibiting the formation of the polymer matrix, suppressing cell adhesion and attachment, and decreasing the virulence factors' production, thereby blocking the quorum sensing network. Here, we focus on plant derived chemicals, and provide an updated literature review on the anti-biofilm properties of terpenes, flavonoids, alkaloids, and phenolic compounds. Moreover, whenever information is available, we also report the mechanisms of action.

Steroid Derivatives as Potential Antimicrobial Agents Against Staphylococcus aureus Planktonic Cells

In this work, the antibacterial activity of deflazacort and several of its synthetic precursors was tested against a panel of bacterial pathogens responsible for most drug-resistant infections including Staphylococcus aureus, Enterococcus spp., Acinetobacter baumannii, Pseudomonas aeruginosa, Klebsiella pneumoniae, Escherichia coli, and Enterobacter spp. The derivative of deflazacort, PYED-1 (pregnadiene-11-hydroxy-16α,17α-epoxy-3,20-dione-1) showed the best antibacterial activity in a dose-dependent way. We focused on the action of PYED-1 against S. aureus cells. PYED-1 exhibited an additive antimicrobial effect with gentamicin and oxacillin against the methicillin-resistant S. aureus isolate 00717. In addition to its antimicrobial effect, PYED-1 was found to repress the expression of several virulence factors of S. aureus, including toxins encoded by the hla (alpha-haemolysin), hlb (beta-haemolysin), lukE-D (leucotoxins E-D), and sea (staphylococcal enterotoxin A) genes, and cell surface factors (fnbB (fibronectin-binding protein B) and capC (capsule biosynthesis protein C)). The expression levels of autolysin isaA (immunodominant staphylococcal antigen) were also increased.

Antimicrobial and Antivirulence Action of Eugenia brejoensis Essential Oil in vitro and in vivo Invertebrate Models

Eugenia brejoensis L. (Myrtaceae) is an endemic plant from caatinga ecosystem (brazilian semi-arid) which have an E. brejoensis essential oil (EbEO) with reported antimicrobial activity. In this work, in vitro and in vivo models were used to characterize the inhibitory effects of EbEO in relation to Staphylococcus aureus. EbEO inhibited the growth of all tested S. aureus strains (including multidrug resistance isolates) with values ranging from 8 to 516 μg/mL. EbEO also synergistically increased the action of ampicillim, chloramphenicol, and kanamycin. The treatment with subinhibitory concentrations (Sub-MIC) of EbEO decreased S. aureus hemolytic activity and its ability to survive in human blood. EbEO strongly reduced the levels of staphyloxanthin (STX), an effect related to increased susceptibility of S. aureus to hydrogen peroxide. The efficacy of EbEO against S. aureus was further demonstrated using Caenorhabditis elegans and Galleria mellonella. EbEO increased the lifespan of both organisms infected by S. aureus, reducing the bacterial load. In addition, EbEO reduced the severity of S. aureus infection in G. mellonella, as shown by lower levels of melanin production in those larvae. In summary, our data suggest that EbEO is a potential source of lead molecules for development of new therapeutic alternatives against S. aureus.

Subinhibitory Concentrations of Fusidic Acid May Reduce the Virulence of S. aureus by Down-Regulating sarA and saeRS to Reduce Biofilm Formation and α-Toxin Expression

Staphylococcus aureus is an important pathogen in hospital and community infections. Fusidic acid is particularly effective in treating skin and wound infections caused by staphylococci. The purpose of our study was to clarify the effect of fusidic acid on the biofilm formation and α-toxin expression of S. aureus at subinhibitory concentrations [1/64, 1/32, and 1/16 × minimum inhibitory concentration (MIC)]. A total of 504 genes greater than a twofold or less than twofold change in expression of S. aureus effected by subinhibitory concentrations of fusidic acid were found, including 232 up-regulated genes and 272 down-regulated genes, which were determined by transcriptome sequencing. Our results showed subinhibitory concentrations of fusidic acid significantly inhibited the expression of hla, spa, icaA, and cidA at the mRNA level in clinical S. aureus strains tested. And subinhibitory concentrations of fusidic acid can significantly reduce the hemolysis activity and α-toxin production of S. aureus. In addition, the subinhibitory concentrations of fusidic acid significantly inhibited biofilm formation, autolysis, cell aggregation, and polysaccharide intercellular adhesin (PIA) production of S. aureus. Moreover, fusidic acid effectively reduces the damage of mouse skin lesion area. Furthermore, fusidic acid reduced the expression of the two-component regulatory system saeRS and staphylococcal accessory gene regulator (sarA). In conclusion, our results suggested that the subinhibitory concentrations of fusidic acid may reduce the virulence of S. aureus by down-regulating sarA and saeRS to reduce biofilm formation and α-toxin expression, which will provide a theoretical basis for the clinical treatment of S. aureus infection. This is the first report that fusidic acid has an inhibitory effect on the virulence of S. aureus, and this broadens the clinical application of fusidic acid.

The Role of Drug Repurposing in the Development of Novel Antimicrobial Drugs: Non-Antibiotic Pharmacological Agents as Quorum Sensing-Inhibitors

Background: The emergence of multidrug-resistant organisms (MDROs) is a global public health issue, severely hindering clinicians in administering appropriate antimicrobial therapy. Drug repurposing is a drug development strategy, during which new pharmacological applications are identified for already approved drugs. From the viewpoint of the development of virulence inhibitors, inhibition of quorum sensing (QS) is a promising route because various important features in bacterial physiology and virulence are mediated by QS-dependent gene expression. Methods: Forty-five pharmacological agents, encompassing a wide variety of different chemical structures and mechanisms of action, were tested during our experiments. The antibacterial activity of the compounds was tested using the broth microdilution method. Screening and semi-quantitative assessment of QS-inhibition by the compounds was performed using QS-signal molecule-producing and indicator strains. Results: Fourteen pharmaceutical agents showed antibacterial activity in the tested concentration range, while eight drugs (namely 5-fluorouracil, metamizole-sodium, cisplatin, methotrexate, bleomycin, promethazine, chlorpromazine, and thioridazine) showed dose-dependent QS-inhibitory activity in the in vitro model systems applied during the experiments. Conclusions: Virulence inhibitors represent an attractive alternative strategy to combat bacterial pathogens more efficiently. Some of the tested compounds could be considered potential QS-inhibitory agents, warranting further experiments involving additional model systems to establish the extent of their efficacy.

Natural Products That Target Virulence Factors in Antibiotic-Resistant Staphylococcus aureus

The increase in the incidence of antibiotic-resistant Staphylococcus aureus (S. aureus) associated infections necessitates the urgent development of novel therapeutic strategies and antibacterial drugs. Antivirulence strategy is an especially compelling alternative strategy due to its low selective pressure for the development of drug resistance in bacteria. Plants and microorganisms are not only important food and medicinal resources but also serve as sources for the discovery of natural products that target bacterial virulence factors. This review discusses the mechanisms of the major virulence factors of S. aureus, including the accessory gene regulator quorum-sensing system, bacterial biofilm formation, α-hemolysin, sortase A, and staphyloxanthin. We also provide an overview of natural products isolated from plants and microorganisms with activity against the major virulence factors of S. aureus and their adjuvant effects on existing antibiotics to overcome antibiotic-resistant S. aureus. Finally, the limitations and solutions of these antivirulence compounds are discussed, which will help in the development of novel antibacterial drugs against antibiotic-resistant S. aureus.

Downregulated Expression of Virulence Factors Induced by Benzyl Isothiocyanate in Staphylococcus Aureus: A Transcriptomic Analysis

Staphylococcus aureus (S. aureus) is a common foodborne pathogen that leads to various diseases; therefore, we urgently need to identify different means to control this harmful pathogen in food. In this study, we monitored the transcriptional changes of S. aureus by RNA-seq analysis to better understand the effect of benzyl isothiocyanate (BITC) on the virulence inhibition of S. aureus and determined the bacteriostatic effect of BITC at subinhibitory concentrations. Our results revealed that, compared with the control group (SAC), the BITC-treated experimental group (SAQ_BITC) had 708 differentially expressed genes (DEGs), of which 333 genes were downregulated and the capsular polysaccharide (cp) was significantly downregulated. Furthermore, we screened five of the most virulent factors of S. aureus, including the capsular polysaccharide biosynthesis protein (cp5D), capsular polysaccharide synthesis enzyme (cp8F), thermonuclease (nuc), clumping factor (clf), and protein A (spa), and verified the accuracy of these significantly downregulated genes by qRT-PCR. At the same time, we used light microscopy, scanning electron microscopy (SEM) and inverted fluorescence microscopy (IFM) to observe changes in biofilm associated with the cp5D and cp8F. Therefore, these results will help to further study the basis of BITC for the antibacterial action of foodborne pathogenic bacteria.

Phylogenetic and Molecular Profile of Staphylococcus aureus Isolated from Bloodstream Infections in Northeast Brazil

Staphylococcus aureus is a notorious human pathogen associated with serious nosocomial and community-acquired infections, such as pneumonia, meningitis, endocarditis, toxic shock syndrome, and sepsis, among others. The objective of this study was to investigate the molecular profile, antimicrobial resistance, and clonal diversity of S. aureus isolated from the bloodstream. The determination of the minimum inhibitory concentration (MIC) of the antimicrobial was performed by an automated method. The presence of several virulence and resistance genes was evaluated by PCR. In addition, multilocus sequence typing (MLST) was used to analyze the clonal diversity of S. aureus. A high resistance to oxacillin (78%), clindamycin (78%), erythromycin (70%), ciprofloxacin (61%), and gentamicin (52%) was observed among the isolates. In most of them, the following virulence genes were detected: hlb (83%), ebpS (61%), icaA (57%), fnbpA (17%), and clfA (13%). Only one isolate carried the pvl gene. MLST analysis identified five new sequence types (STs): 5429, 5430, 5431, 5432, and 5433, as well as another seven-ST5, ST97, ST398, ST101, ST30, ST461, and ST2779-among the remaining strains. These seven STs and the four new STs are clustered in four clonal complexes: CC1, CC2, CC7, and CC17. Phylogenetic analysis showed the genetic relationship of the five new ST strains with another 18 strains. Altogether, these analyses indicate the horizontal transfer acquisition of virulence factor genes and multidrug resistance.

Recent Advances in Anti-virulence Therapeutic Strategies With a Focus on Dismantling Bacterial Membrane Microdomains, Toxin Neutralization, Quorum-Sensing Interference and Biofilm Inhibition

Antimicrobial resistance constitutes one of the major challenges facing humanity in the Twenty-First century. The spread of resistant pathogens has been such that the possibility of returning to a pre-antibiotic era is real. In this scenario, innovative therapeutic strategies must be employed to restrict resistance. Among the innovative proposed strategies, anti-virulence therapy has been envisioned as a promising alternative for effective control of the emergence and spread of resistant pathogens. This review presents some of the anti-virulence strategies that are currently being developed, it will cover strategies focused on quench pathogen quorum sensing (QS) systems, disassemble of bacterial functional membrane microdomains (FMMs), disruption of biofilm formation and bacterial toxin neutralization.