Sesamin and sesamolin rescues Caenorhabditis elegans from Pseudomonas aeruginosa infection through the attenuation of quorum sensing regulated virulence factors

Quercetin: a promising virulence inhibitor of Pseudomonas aeruginosa LasB in vitro

With the inappropriate use of antibiotics, antibiotic resistance has emerged as a major dilemma for patients infected with Pseudomonas aeruginosa. Elastase B (LasB), a crucial extracellular virulence factor secreted by P. aeruginosa, has been identified as a key target for antivirulence therapy. Quercetin, a natural flavonoid, exhibits promising potential as an antivirulence agent. We aim to evaluate the impact of quercetin on P. aeruginosa LasB and elucidate the underlying mechanism. Molecular docking and molecular dynamics simulation revealed a rather favorable intermolecular interaction between quercetin and LasB. At the sub-MICs of ≤256 μg/ml, quercetin was found to effectively inhibit the production and activity of LasB elastase, as well as downregulate the transcription level of the lasB gene in both PAO1 and clinical strains of P. aeruginosa. Through correlation analysis, significant positive correlations were shown between the virulence gene lasB and the QS system regulatory genes lasI, lasR, rhlI, and rhlR in clinical strains of P. aeruginosa. Then, we found the lasB gene expression and LasB activity were significantly deficient in PAO1 ΔlasI and ΔlasIΔrhlI mutants. In addition, quercetin significantly downregulated the expression levels of regulated genes lasI, lasR, rhlI, rhlR, pqsA, and pqsR as well as effectively attenuated the synthesis of signaling molecules 3-oxo-C12-HSL and C4-HSL in the QS system of PAO1. Quercetin was also able to compete with the natural ligands OdDHL, BHL, and PQS for binding to the receptor proteins LasR, RhlR, and PqsR, respectively, resulting in the formation of more stabilized complexes. Taken together, quercetin exhibits enormous potential in combating LasB production and activity by disrupting the QS system of P. aeruginosa in vitro, thereby offering an alternative approach for the antivirulence therapy of P. aeruginosa infections. KEY POINTS: • Quercetin diminished the content and activity of LasB elastase of P. aeruginosa. • Quercetin inhibited the QS system activity of P. aeruginosa. • Quercetin acted on LasB based on the QS system.

Effect of a phthalate derivative purified from Bacillus zhangzhouensis SK4 on quorum sensing regulated virulence factors of Pseudomonas aeruginosa

Pseudomonas aeruginosa causes life-threatening diseases and is resistant to almost all conventional antibiotics. The quorum sensing (QS) system of P. aeruginosa contributes to many pathogenic factors some of which are pigment production, motility, and biofilm. The disruption of quorum sensing system may be an impactful strategy to deal with infections. The present study investigates the anti-quorum sensing property of a bioactive molecule extracted from marine epibiotic bacteria present on the surface of seaweeds. Among all the isolates tested against monitor strain Chromobacterium violaceum (MTCC 2656), the one with the highest activity was identified as Bacillus zhangzhouensis SK4. The culture supernatant was extracted with chloroform which was then partially purified by TLC and column chromatography. The probable anti-QS compound was identified as 1,2-benzenedicarboxylic acid, bis (2-methylpropyl ester) by GC-MS and NMR analysis. The treatment of P. aeruginosa MCC 3457 with the lead compound resulted in the reduced production of pyocyanin, rhamnolipids, exopolysaccharide, biofilm, and motility. The observations of light and scanning electron microscopy also supported the biofilm inhibition. The lead compound showed synergism with the meropenem antibiotic and significantly reduced MIC. The molecular docking and pharmacokinetics study predicted 1, 2-benzenedicarboxylic acid, bis (2-methylpropyl ester), a phthalate derivative as a good drug candidate. The molecular dynamics study was also performed to check the stability of the lead compound and LasR complex. Further, lead compounds did not exhibit any cytotoxicity when tested on human embryonic kidney cells. As per our knowledge, this is the first report on the anti-QS activity of B. zhangzhouensis SK4, indicating that epibiotic bacteria can be a possible source of novel compounds to deal with the multidrug resistance phenomenon.

Sesame Seeds: A Nutrient-Rich Superfood

Sesame seeds (Sesamum indicum L.) have been cultivated for thousands of years and have long been celebrated for their culinary versatility. Beyond their delightful nutty flavor and crunchy texture, sesame seeds have also gained recognition for their remarkable health benefits. This article provides an in-depth exploration of the numerous ways in which sesame seeds contribute to overall well-being. Sesame seeds are a powerhouse of phytochemicals, including lignans derivatives, tocopherol isomers, phytosterols, and phytates, which have been associated with various health benefits, including the preservation of cardiovascular health and the prevention of cancer, neurodegenerative disorders, and brain dysfunction. These compounds have also been substantiated for their efficacy in cholesterol management. Their potential as a natural source of beneficial plant compounds is presented in detail. The article further explores the positive impact of sesame seeds on reducing the risk of chronic diseases thanks to their rich polyunsaturated fatty acids content. Nevertheless, it is crucial to remember the significance of maintaining a well-rounded diet to achieve the proper balance of n-3 and n-6 polyunsaturated fatty acids, a balance lacking in sesame seed oil. The significance of bioactive polypeptides derived from sesame seeds is also discussed, shedding light on their applications as nutritional supplements, nutraceuticals, and functional ingredients. Recognizing the pivotal role of processing methods on sesame seeds, this review discusses how these methods can influence bioactive compounds. While roasting the seeds enhances the antioxidant properties of the oil extract, certain processing techniques may reduce phenolic compounds.

Duration of fermentation affects microbiome composition and biological activity of an Indian traditional formulation - Panchagavya

OBJECTIVE

This study aimed at investigating whether the duration of fermenting Panchagavya (PG) preparation in copper vessel affects its biological activity and microbiome composition.

MATERIALS AND METHODS

Prophylactic potential of PG against bacterial infection was assessed through an in vivo assay employing the nematode worm Caenorhabditis elegans as a model host. Bacterial diversity of the PG samples was revealed through metagenomic analysis.

RESULTS

Duration of fermentation was found to affect biological activity as well as microbiome composition of the PG samples. PG-samples fermented ≥60 min lost their prophylactic potential, and develop anthelmintic activity. Bacterial phyla whose relative abundance was significantly different between the prophylactic and anthelmintic PG samples were Planctomycetota, Proteabacteria, Bacteroidota, Verrucomicrobiota, Patescibacteria, Acidobacteriota, Chloroflexi, Firmicutes and Campilobacterota.

CONCLUSION

This study validates the prophylactic potential of Panchagavya against bacterial pathogens, and shows that duration of the fermentation time while preparing PG can have profound effect on its biological activities. Biological activities of PG samples seem to have a correlation with their inherent microbial community. Metagenomic profiling can be an effective tool for standardization of PG formulations.

Macrolides impact the growth ability of clinical Pseudomonas aeruginosa through quorum-sensing systems

The aim of the present study was to examine the impact of macrolides on the expression of virulence factors and QS-associated genes in clinical P. aeruginosa isolates. Among 60 clinical P. aeruginosa, pyocyanin production was detected in 27 (45%) isolates, which belonged to various STs. Erythromycin inhibited the production of pigments in 12 out of 27 isolates. Other antibiotic categories didn't have an impact on production of pigments. Additionally, results showed that erythromycin sub-MIC inhibited the growth-rate in 17 isolates. Of note, in six isolates, the inhibition of growth-rate was greater when using both erythromycin and meropenem than using each antibiotic individually. Finally, addition of erythromycin down-regulated the expression of QS-associated genes (65.5%-81.3%) and almost all virulence-associated genes. In conclusion, our results confirmed that macrolides could be used in combination with last-line antibiotics, such as carbapenems, to treat infections caused by multidrug-resistant Gram-negative bacteria.

Repurposing albendazole as a potent inhibitor of quorum sensing-regulated virulence factors in Pseudomonas aeruginosa: Novel prospects of a classical drug

Pseudomonas aeruginosa has emerged as a critical superbug that poses a serious threat to public health. Owing to its virulence and multidrug resistance profiles, the pathogen demands immediate attention for devising alternate intervention strategies. In an attempt to repurpose drugs against P. aeruginosa, this preclinical study was aimed at investigating the antivirulence prospects of albendazole (AbZ), an FDA-approved anti-helminthic drug, recently predicted to disrupt quorum sensing (QS) in Chromobacterium violaceum. AbZ was scrutinized for its quorum quenching (QQ) prospects, effect on bacterial virulence, different motility phenotypes, and biofilm formation in vitro. Additionally, in silico analysis was employed to predict the molecular interactions between AbZ and QS receptors. At sub-inhibitory levels, AbZ demonstrated anti-QS activity and significantly abrogated AHL biosynthesis in P. aeruginosa. Moreover, AbZ significantly downregulated the transcript levels of QS- (lasI/lasR, rhlI/rhlR, and pqsA/pqsR) and QS-dependent virulence (aprA, lasA, lasB, plcH, and toxA) genes in P. aeruginosa. This coincided with reduced hemolysin, alginate, pyocyanin, rhamnolipids, total protease, and elastase production, thereby lowering phenotypic virulence. Molecular docking with AbZ further revealed strong associations and high binding energies with LasR (-8.8 kcal/mol), RhlR (-6.5 kcal/mol), and PqsR (-6.3 kcal/mol) receptors. AbZ also impeded bacterial motility and abolished EPS production, severely compromising pseudomonal biofilm formation. For the first time, AbZ was shown to interfere with QS circuitry and consequently disarming pseudomonal virulence. Hence, AbZ can be exploited for its antivirulence properties against P. aeruginosa.

Eradication of Pseudomonas aeruginosa biofilm using quercetin-mediated copper oxide nanoparticles incorporated in the electrospun polycaprolactone nanofibrous scaffold

Pseudomonas aeruginosa is an opportunistic bacterial pathogen that form biofilms in chronic wounds and is difficult to treat with standard treatment methods. In the present study, flavonoid quercetin-mediated CuONPs (Que-CuONPs) were successfully synthesized and incorporated in the electrospun polycaprolactone (Que-CuONPs-PCL) nanofibrous membrane to eradicate the burn wound infection causing P. aeruginosa biofilm. The fabricated scaffold Que-CuONPs-PCL was characterized using HR-SEM, EDX, XRD, and FTIR. The synthesized Que-CuONPs appeared as spherical in shape with the average size of 36 nm. The crystallite size of the synthesized CuONPs was calculated as 23 nm. Antibacterial activity results shows that the ZOI and MIC of Que-CuONPs against P. aeruginosa was found to be 20 mm and 5 μg/mL, respectively. Antibiofilm assay results indicate the pre-formed P. aeruginosa biofilm was completely eradicated by Que-CuONPs at 8-MIC. The Que-CuONPs-PCL nanofibrous scaffolds exhibits less cytotoxic effects on mouse fibroblast (L929) cells. Finally, this study highlights the fabricated Que-CuONPs-PCL nanofibrous scaffolds exhibits an excellent antibiofilm effect against P. aeruginosa biofilm with a great biocompatibility.

Synergistic Effect of Plant Compounds in Combination with Conventional Antimicrobials against Biofilm of Staphylococcus aureus, Pseudomonas aeruginosa, and Candida spp

Bacterial and fungal biofilm has increased antibiotic resistance and plays an essential role in many persistent diseases. Biofilm-associated chronic infections are difficult to treat and reduce the efficacy of medical devices. This global problem has prompted extensive research to find alternative strategies to fight microbial chronic infections. Plant bioactive metabolites with antibiofilm activity are known to be potential resources to alleviate this problem. The phytochemical screening of some medicinal plants showed different active groups, such as stilbenes, tannins, alkaloids, terpenes, polyphenolics, flavonoids, lignans, quinones, and coumarins. Synergistic effects can be observed in the interaction between plant compounds and conventional drugs. This review analyses and summarises the current knowledge on the synergistic effects of plant metabolites in combination with conventional antimicrobials against biofilms of Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans. The synergism of conventional antimicrobials with plant compounds can modify and inhibit the mechanisms of acquired resistance, reduce undesirable effects, and obtain an appropriate therapeutic effect at lower doses. A deeper knowledge of these combinations and of their possible antibiofilm targets is needed to develop next-generation novel antimicrobials and/or improve current antimicrobials to fight drug-resistant infections attributed to biofilm.

Study of Antimicrobial Resistance, Biofilm Formation, and Motility of Pseudomonas aeruginosa Derived from Urine Samples

Pseudomonas aeruginosa causes urinary tract infections associated with catheters by forming biofilms on the surface of indwelling catheters. Therefore, controlling the spread of the bacteria is crucial to preventing its transmission in hospitals and the environment. Thus, our objective was to determine the antibiotic susceptibility profiles of twenty-five P. aeruginosa isolates from UTIs at the Medical Center of Trás-os-Montes and Alto Douro (CHTMAD). Biofilm formation and motility are also virulence factors studied in this work. Out of the twenty-five P. aeruginosa isolates, 16% exhibited multidrug resistance, being resistant to at least three classes of antibiotics. However, the isolates showed a high prevalence of susceptibility to amikacin and tobramycin. Resistance to carbapenem antibiotics, essential for treating infections when other antibiotics fail, was low in this study, Notably, 92% of the isolates demonstrated intermediate sensitivity to ciprofloxacin, raising concerns about its efficacy in controlling the disease. Genotypic analysis revealed the presence of various β-lactamase genes, with class B metallo-β-lactamases (MBLs) being the most common. The bla_NDM, bla_SPM, and bla_VIM-VIM2 genes were detected in 16%, 60%, and 12% of the strains, respectively. The presence of these genes highlights the emerging threat of MBL-mediated resistance. Additionally, virulence gene analysis showed varying prevalence rates among the strains. The exoU gene, associated with cytotoxicity, was found in only one isolate, while other genes such as exoS, exoA, exoY, and exoT had a high prevalence. The toxA and lasB genes were present in all isolates, whereas the lasA gene was absent. The presence of various virulence genes suggests the potential of these strains to cause severe infections. This pathogen demonstrated proficiency in producing biofilms, as 92% of the isolates were found to be capable of doing so. Currently, antibiotic resistance is one of the most serious public health problems, as options become inadequate with the continued emergence and spread of multidrug-resistant strains, combined with the high rate of biofilm production and the ease of dissemination. In conclusion, this study provides insights into the antibiotic resistance and virulence profiles of P. aeruginosa strains isolated from human urine infections, highlighting the need for continued surveillance and appropriate therapeutic approaches.

Therapeutic Potential of Phenolic Compounds in Medicinal Plants-Natural Health Products for Human Health

Phenolic compounds and flavonoids are potential substitutes for bioactive agents in pharmaceutical and medicinal sections to promote human health and prevent and cure different diseases. The most common flavonoids found in nature are anthocyanins, flavones, flavanones, flavonols, flavanonols, isoflavones, and other sub-classes. The impacts of plant flavonoids and other phenolics on human health promoting and diseases curing and preventing are antioxidant effects, antibacterial impacts, cardioprotective effects, anticancer impacts, immune system promoting, anti-inflammatory effects, and skin protective effects from UV radiation. This work aims to provide an overview of phenolic compounds and flavonoids as potential and important sources of pharmaceutical and medical application according to recently published studies, as well as some interesting directions for future research. The keyword searches for flavonoids, phenolics, isoflavones, tannins, coumarins, lignans, quinones, xanthones, curcuminoids, stilbenes, cucurmin, phenylethanoids, and secoiridoids medicinal plant were performed by using Web of Science, Scopus, Google scholar, and PubMed. Phenolic acids contain a carboxylic acid group in addition to the basic phenolic structure and are mainly divided into hydroxybenzoic and hydroxycinnamic acids. Hydroxybenzoic acids are based on a C6-C1 skeleton and are often found bound to small organic acids, glycosyl moieties, or cell structural components. Common hydroxybenzoic acids include gallic, syringic, protocatechuic, p-hydroxybenzoic, vanillic, gentistic, and salicylic acids. Hydroxycinnamic acids are based on a C6-C3 skeleton and are also often bound to other molecules such as quinic acid and glucose. The main hydroxycinnamic acids are caffeic, p-coumaric, ferulic, and sinapic acids.

α-Terpineol synergizes with gentamicin to rescue Caenorhabditis elegans from Pseudomonas aeruginosa infection by attenuating quorum sensing-regulated virulence

AIMS

This study scrutinized α-Terpineol (α-T) for its anti-virulence and anti-fouling potential against P. aeruginosa PAO1 in conjunction with gentamicin (GeN) using in-vitro, in-silico, and in-vivo approaches.

MAIN METHODS

The quorum quenching (QQ) potential of the drug combination was studied using a quorum sensing (QS) biosensor strain and tested for synergy using chequerboard and time-kill kinetics assays. The effect of α-T and GeN on bacterial motility, QS-regulated virulence factor production, and biofilm formation was assessed in P. aeruginosa PAO1 along with molecular docking analysis. The protective effects of α-T-GeN combination were also examined in a Caenorhabditis elegans infection model through slow-killing (SK) assays.

KEY FINDINGS

The drug combination displayed synergy, enhanced QQ activity, and suppressed AHL production in PAO1. At sub-inhibitory concentrations, the drug combination suppressed the expression of genes regulating QS and pseudomonal virulence, thereby inhibiting the production of virulence factors in PAO1. The drug combination compromised all forms of pseudomonal motility, strongly inhibited biofilm formation, and successfully eradicated preformed biofilms. Based on these findings, it is concluded that GeN (alone) does not harbor any QQ properties, but enhances the QQ potential of α-T. Moreover, combinational treatment protected C. elegans from pseudomonal infection and improved survival rates by 73 % at 96 h.

SIGNIFICANCE

For the first time, the molecular mechanism responsible for the anti-QS activity of α-T was unraveled through a comprehensive investigation, thereby asserting its potential as an anti-virulent drug against P. aeruginosa.

An inhibitory effect of schisandrone on α-hemolysin expression to combat methicillin-resistant staphylococcus aureus infections

Due to increasing antibiotic resistance, targeting bacterial virulence factors is now gaining further interest as an alternative strategy to develop novel classes of anti-infective agents. The critical role of α-hemolysin (Hla), an indispensable virulence determinant, in the pathogenicity of Staphylococcus aureus renders this virulence factor an appealing target for effective therapeutic applications. Herein, we identified a natural compound schisandraone, as an effective Hla inhibitor, which could inhibit Hla production and thus hemolytic activity in a dose-dependent manner without affecting the growth of S. aureus. We also found that the addition of schisandrone could down-regulate the transcriptional levels of the hla, agrA and RNAIII and significantly alleviated Hla-mediated injury of A549 cells co-cultured with S. aureus. In vivo studies further suggested that schisandrone combined with antibiotic ceftiofur exhibited a significant therapeutic effect on S. aureus infection. These findings revealed the role of schisandrone in inhibiting the activity of Hla and we believe that it is a promising anti-virulence candidate to combat MRSA pneumonia.

The Preyssler-Type Polyoxotungstate Exhibits Anti-Quorum Sensing, Antibiofilm, and Antiviral Activities

The increase in bacterial resistance to antibiotics has led researchers to find new compounds or find combinations between different compounds with potential antibacterial action and with the ability to prevent the development of antibiotic resistance. Polyoxotungstates (POTs) are inorganic clusters that may fulfill that need, either individually or in combination with antibiotics. Herein, we report the ability of the polyoxotungstates (POTs) with Wells-Dawson P2W18, P2W17, P2W15, and Preyssler P5W30 type structures to differently affect Gram-negative and Gram-positive microorganisms, either susceptible or resistant to antibiotics. The compound P5W30 showed the highest activity against the majority of the tested bacterial strains in comparison with the other tested POTs (P2W15, P2W17 and P2W18) that did not show inhibition zones for the Gram-negative bacteria, A. baumanii I73775, E. coli DSM 1077, E. coli I73194, K. pneumoniae I7092374, and P. aeruginosa C46281). Generally, the results evidenced that Gram-positive bacteria are more susceptible to the POTs tested. The compound P5W30 was the one most active against S. aureus ATCC 6538 and MRSA16, reaching <0.83 mg·mL−1 (100 μM) and 4.96 mg·mL−1 (600 μM), respectively. Moreover, it was verified by NMR spectroscopy that the most promising POT, P5W30, remains intact under all the experimental conditions, after 24 h at 37 °C. This prompted us to further evaluate the anti-quorum sensing activity of P5W30 using the biosensor Chromobacterium violaceum CV026, as well as its antibiofilm activity both individually and in combination with the antibiotic cefoxitin against the methicillin-resistant Staphylococcus aureus 16 (MRSA16). P5W30 showed a synergistic antibacterial effect with the antibiotic cefoxitin and chloramphenicol against MRSA16. Moreover, the antibiofilm activity of P5W30 was more pronounced when used individually, in comparison with the combination with the antibiotic cefoxitin. Finally, the antiviral activity of P5W30 was tested using the coliphage Qβ, showing a dose-dependent response. The maximum inactivation was observed at 750 μM (6.23 mg·mL−1). In sum, P5W30 shows anti-quorum sensing and antibiofilm activities besides being a potent antibacterial agent against S. aureus and to exhibit antiviral activities against enteric viruses.

Targeting the Holy Triangle of Quorum Sensing, Biofilm Formation, and Antibiotic Resistance in Pathogenic Bacteria

Chronic and recurrent bacterial infections are frequently associated with the formation of biofilms on biotic or abiotic materials that are composed of mono- or multi-species cultures of bacteria/fungi embedded in an extracellular matrix produced by the microorganisms. Biofilm formation is, among others, regulated by quorum sensing (QS) which is an interbacterial communication system usually composed of two-component systems (TCSs) of secreted autoinducer compounds that activate signal transduction pathways through interaction with their respective receptors. Embedded in the biofilms, the bacteria are protected from environmental stress stimuli, and they often show reduced responses to antibiotics, making it difficult to eradicate the bacterial infection. Besides reduced penetration of antibiotics through the intricate structure of the biofilms, the sessile biofilm-embedded bacteria show reduced metabolic activity making them intrinsically less sensitive to antibiotics. Moreover, they frequently express elevated levels of efflux pumps that extrude antibiotics, thereby reducing their intracellular levels. Some efflux pumps are involved in the secretion of QS compounds and biofilm-related materials, besides being important for removing toxic substances from the bacteria. Some efflux pump inhibitors (EPIs) have been shown to both prevent biofilm formation and sensitize the bacteria to antibiotics, suggesting a relationship between these processes. Additionally, QS inhibitors or quenchers may affect antibiotic susceptibility. Thus, targeting elements that regulate QS and biofilm formation might be a promising approach to combat antibiotic-resistant biofilm-related bacterial infections.

Making Sense of Quorum Sensing at the Intestinal Mucosal Interface

The gut microbiome can produce metabolic products that exert diverse activities, including effects on the host. Short chain fatty acids and amino acid derivatives have been the focus of many studies, but given the high microbial density in the gastrointestinal tract, other bacterial products such as those released as part of quorum sensing are likely to play an important role for health and disease. In this review, we provide of an overview on quorum sensing (QS) in the gastrointestinal tract and summarise what is known regarding the role of QS molecules such as auto-inducing peptides (AIP) and acyl-homoserine lactones (AHL) from commensal, probiotic, and pathogenic bacteria in intestinal health and disease. QS regulates the expression of numerous genes including biofilm formation, bacteriocin and toxin secretion, and metabolism. QS has also been shown to play an important role in the bacteria–host interaction. We conclude that the mechanisms of action of QS at the intestinal neuro–immune interface need to be further investigated.

Alantolactone modulates the production of quorum sensing mediated virulence factors and biofilm formation in Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen in immunocompromised patients and accounts for mortality worldwide. Quorum sensing (QS) and QS mediated biofilm formation of P. aeruginosa increase the severity of infection in the host. New and effective therapeutics are in high demand to eliminate Pseudomonas infections. The current study investigated the quorum quenching and biofilm inhibition properties of alantolactone (ATL) against P. aeruginosa PAO1. The production of key virulence factors and biofilm components were affected in bacteria when treated with sub-MIC of ATL and further validated by qRT-PCR studies. The anti-infective potential of ATL was corroborated in an in vivo model with improved survival of infected Caenorhabditis elegans and reduced bacterial colonization. In silico studies suggested the molecular interactions of ATL to QS proteins as stable. Finally, ATL was explored in the present study to inhibit QS pathways and holds the potential to develop into an effective anti-infective agent against P. aeruginosa.

The Untargeted Phytochemical Profile of Three Meliaceae Species Related to In Vitro Cytotoxicity and Anti-Virulence Activity against MRSA Isolates

BACKGROUND

A high mortality rate is associated with about 80% of all infections worldwide, mainly due to antimicrobial resistance. Various antimicrobial and cytotoxic activities have been proposed for Meliaceae species. This study aimed to evaluate the in vitro anti-virulence and cytotoxic effect of the leaf extracts of Aphanamixis polystachya, Toona ciliata and Melia azedarach against five MRSA strains and on three cancer cell lines, followed by biological correlation to their encompassed phytoconstituents.

MATERIAL AND METHODS

We explored three plants of this family against a panel of Methicillin-resistant Staphylococcus aureus (MRSA) strains and several cancer cell lines to select the most promising candidates for further in vivo and preclinical studies. The phytochemical composition was evaluated by UHPLC-QTOF-MS untargeted profiling. Cell viability was assessed by SRB assay. Minimum Inhibitory Concentration was carried out by using the agar micro-dilution technique. Inhibition of biofilm formation and preformed biofilm disruption were assessed spectrophotomertically, according to the Sultan and Nabil method (2019).

RESULTS

A total of 279 compounds were putatively annotated to include different phytochemical classes, such as flavonoids (108), limonoids/terpenoids (59), phenolic acids (49) and lower-molecular-weight phenolics (39). A. polystachya extract showed the most potent cytotoxic activity against Huh-7, DU-145 and MCF-7 cell lines (IC₅₀ = 3, 3.5 and 13.4 µg mL^-1, respectively), followed by M. azedarach, with no effect recorded for T. ciliata extract. Furthermore, both A. polystachya and M. azedarach extracts showed promising anti-virulence and antimicrobial activities, with A. polystachya being particularly active against MRSA. These two latter extracts could inhibit and disrupt the biofilm, formed by MRSA, at sub-lethal concentrations. Interestingly, the extracts inhibited hemolysin-α enzyme, thus protecting rabbit RBCs from lysis. A. polystachya extract reduced the pigmentation and catalase enzyme activity of tested pigmented strains better than M. azedarach at both tested sub-MICs. Consequently, susceptibility of the extract-treated cells to oxidant killing by 200 mM H₂O₂ increased, leading to faster killing of the cells within 120 min as compared to the extract-non-treated cells, likely due to the lower antioxidant-scavenging activity of cells exhibiting less staphyloxanthin production.

CONCLUSION

These findings suggested that both A. polystachya and M. azedarach natural extracts are rich in bioactive compounds, mainly limonoids, phenolics and oxygenated triterpenoids, which can combat MRSA biofilm infections and could be considered as promising sources of therapeutic cytotoxic, antibiofilm and anti-virulence agents.

The mechanism of microglia-mediated immune inflammation in ischemic stroke and the role of natural botanical components in regulating microglia: A review

Ischemic stroke (IS) is one of the most fatal diseases. Neuroimmunity, inflammation, and oxidative stress play important roles in various complex mechanisms of IS. In particular, the early proinflammatory response resulting from the overactivation of resident microglia and the infiltration of circulating monocytes and macrophages in the brain after cerebral ischemia leads to secondary brain injury. Microglia are innate immune cells in the brain that constantly monitor the brain microenvironment under normal conditions. Once ischemia occurs, microglia are activated to produce dual effects of neurotoxicity and neuroprotection, and the balance of the two effects determines the fate of damaged neurons. The activation of microglia is defined as the classical activation (M1 type) or alternative activation (M2 type). M1 type microglia secrete pro-inflammatory cytokines and neurotoxic mediators to exacerbate neuronal damage, while M2 type microglia promote a repairing anti-inflammatory response. Fine regulation of M1/M2 microglial activation to minimize damage and maximize protection has important therapeutic value. This review focuses on the interaction between M1/M2 microglia and other immune cells involved in the regulation of IS phenotypic characteristics, and the mechanism of natural plant components regulating microglia after IS, providing novel candidate drugs for regulating microglial balance and IS drug development.

Antimicrobial Effect of Phytochemicals from Edible Plants

Current strategies of combating bacterial infections are limited and involve the use of antibiotics and preservatives. Each of these agents has generally inadequate efficacy and a number of serious adverse effects. Thus, there is an urgent need for new antimicrobial drugs and food preservatives with higher efficacy and lower toxicity. Edible plants have been used in medicine since ancient times and are well known for their successful antimicrobial activity. Often photosensitizers are present in many edible plants; they could be a promising source for a new generation of drugs and food preservatives. The use of photodynamic therapy allows enhancement of antimicrobial properties in plant photosensitizers. The purpose of this review is to present the verified data on the antimicrobial activities of photodynamic phytochemicals in edible species of the world’s flora, including the various mechanisms of their actions.