Actinomycin D: a novel Pseudomonas aeruginosa quorum sensing inhibitor from the endophyte Streptomyces cyaneochromogenes RC1

Dopamine, an exogenous quorum sensing signaling molecule or a modulating factor in Pseudomonas aeruginosa?

Pseudomonas aeruginosa is recognized globally as an opportunistic pathogen of considerable concern due to its high virulence and pathogenicity, especially in immunocompromised individuals. While research has identified several endogenous quorum sensing (QS) signaling molecules that enhance the virulence and pathogenicity of P. aeruginosa, investigations on exogenous QS signaling molecules or modulating factors remain limited. This study found that dopamine serves as an exogenous QS signaling molecule or modulating factor of P. aeruginosa PAO1, enhancing the production of virulence factors and biofilms. Compared to the control group, treatment with 40 μM dopamine resulted in a 33.1 % increase in biofilm formation, 68.1 % increase in swimming mobility, 63.1 % increase in swarming mobility, 147.2 % increase in the signaling molecule 3-oxo-C12-HSL, and 50.5 %, 28.5 %, 27.0 %, and 33.2 % increases in the virulence factors alginate, rhamnolipids, protease, and pyocyanin, respectively. This study further explored the mechanism of dopamine regulating the biofilm formation and virulence of P. aeruginosa PAO1 through transcriptome and metabolome. Transcriptomic analysis showed that dopamine promoted the expression of virulence genes psl, alg, lasA, rhlABC, rml, and phz in P. aeruginosa PAO1. Metabolomic analysis revealed changes in the concentrations of tryptophan, pyruvate, ethanolamine, glycine, 3-hydroxybutyric acid, and alizarin. Furthermore, KEGG enrichment analysis of altered genes and metabolites indicated that dopamine enhanced phenylalanine, tyrosine, and tryptophan in P. aeruginosa PAO1. The results of this study will contribute to the development of novel exogenous QS signaling molecules or modulating factors and advance our understanding of the interactions between P. aeruginosa and the host environment.

Strategies for quorum sensing inhibition as a tool for controlling Pseudomonas aeruginosa infections

Antibiotic resistance is one of the most important concerns in global health today. A growing number of infections are becoming harder to treat with conventional drugs and fewer new antibiotics are being developed. In this context, strategies based on blocking or attenuating virulence pathways that do not focus on eradication of bacteria are potential therapeutic approaches that should reduce the selective pressure exerted on the pathogen. This virulence depletion can be achieved by inhibiting the conserved quorum sensing (QS) system, a mechanism that enables bacteria to communicate with one another in a density-dependent manner. QS regulates gene expression, leading to the activation of important processes such as virulence and biofilm formation. This review highlights the approaches reported so far for disrupting different steps of the QS system of the multiresistant pathogen Pseudomonas aeruginosa. The authors describe different types of molecules (including enzymes, natural and synthetic small molecules, and antibodies) already identified as P. aeruginosa quorum quenchers (QQs) or QS inhibitors (QSIs), grouped according to the QS circuit that they block (Las, Rhl, Pqs and some examples from the controversial pathway Iqs). The discovery of new QQs and QSIs is expected to help reduce antibiotic doses, or at least to provide options that act as adjuvants to enhance the effect of antibiotic treatment. Moreover, this article outlines the advantages and possible drawbacks of each strategy and provides perspectives on the potential developments in this field in the future.

Isovanillin decreases the virulence regulated by the quorum sensing system of Pseudomonas aeruginosa

The quorum-sensing (QS) system of Pseudomonas aeruginosa dominates the pathogenicity of the acute or chronic infection process. Hence, curbing the pathogenicity of P. aeruginosa by targeting QS system is an ideal strategy. This study aims to identify potential anti-virulence compounds that can effectively disrupt the QS system of P. aeruginosa using a combination of virtual screening and experimental validation techniques. We explored inhibitory effect of isovanillin obtained by virtual screening on P. aeruginosa QS regulated virulence factors extracellular protease, biofilm, and pyocyanin. Results displayed that isovanillin could inhibit the virulence phenotypes regulated by the las- and pqs-QS systems of P. aeruginosa. The synthesis of extracellular proteases, pyocyanin, and biofilm formation by P. aeruginosa were dramatically inhibited by sub-MICs doses of isovanillin. The results of RNA sequencing and quantitative PCR revealed that the QS-activated genes down-regulated by subinhibitory isovanillin in the transcriptional evels. Furthermore, the presence of isovanillin increased the susceptibility of drug-resistant P. aeruginosa to kanamycin, meropenem, and polymyxin B. Treatment of isovanillin as a monotherapy significantly decreased the mortality of C. elegans in P. aeruginosa PAO1 or UCBPP-PA14 (PA14) infection. Our study reported the anti-virulence activity of isovanillin against P. aeruginosa, and provided a structural foundation for developing anti-virulence drugs targeting the QS system of P. aeruginosa.

Exploring the Potential of Bacterial Endophytes in Plant Disease Management

Endophytic bacteria live in the internal tissues of plants, forming symbiotic, mutualistic, commensalistic and trophobiotic relationships. Some are spread via seeds after sprouting from the rhizosphere or phyllosphere. These bacteria capable of promoting plant growth and impart biotic stress by synthesing plant growth hormones, ACC deaminase, organic acids and siderophore. Endophytes aid in phytoremediation by removing soil contaminants and boosting soil fertility via phosphate solubilization and nitrogen fixation. The endophytic microbes are becoming increasingly popular in biotechnological applications which supports sustainable growth of non-food crops for biomass and biofuel. They offer valuable natural materials which is used in medicine, agriculture and industry. Bacterial endophytes are endowed with the enormous potential in the biological treatment of plant pathogens and considered as the superior alternative to synthetic fungicides. The review emphasizes benefits of bacterial endophytes in promoting plant growth and prospects of agricultural applications viz., increasing crop yield under biotic stress condition and their mode of action towards plant diseases. It also summarises the diverse and vital role of endophytes in agroecosystems as well as insights for sustainable agriculture and crop resilience.

Role of fatty acids in modulating quorum sensing in Pseudomonas aeruginosa and Chromobacterium violaceum: an integrated experimental and computational analysis

The broad-spectrum antibacterial capabilities of fatty acids (FAs) and their reduced propensity to promote resistance have rendered as a promising substitute for conventional antibiotics. The structural significance of fatty acid production with the other lipids is a major energy source, and signal transduction has drawn a great deal of research attention to these biomolecules. Saturated and monounsaturated fatty acids reduce virulence by preventing harmful opportunistic bacteria like Pseudomonas aeruginosa and Chromobacterium violaceum from activating their quorum sensing (QS) systems. In this finding, the fatty acids capric acid, caprylic acid, and monoelaidin were selected to evaluate their anti-QS activity against the C. violaceum and P. aeruginosa. At the minimum inhibitory concentration (MIC) and sub-MIC concentration of the three fatty acids, the virulence factor production of both the bacteria was quantified. The virulence factors like EPS, biofilm quantification and visualization, and motility assays were inhibited in the dose-dependent manner (MIC and sub-MIC) for both the organisms whereas this pattern was followed in the pyocyanin, pyoverdine, rhamnolipid, protease of P. aeruginosa and the violacein, and chitinase of C. violaceum. In all these biochemical assays, the capric acid could effectively reduce the production and further validated at gene expression level by RT-qPCR. The study on the gene expression for all these virulence factors reveals that the capric acid inhibited the growth of both the organisms in a higher fold than the caprylic and monoelaidin. The in silico approach of structural validation for the binding of ligands with the proteins in the QS circuit was studied by molecular docking in Schrodinger software. The Las I and Las R in P. aeruginosa and the CviR of C. violaceum protein structures were docked with the selected three fatty acids. The capric acid binds to the pocket with the highest binding score of all the proteins than the caprylic and monoelaidin fatty acids. Thus, capric acid proves to be the therapeutic biomolecule for the anti-QS activity of opportunistic bacteria.

Actinomycin D reduces virulence factors and biofilms against Aeromonas hydrophila

AIMS

Aeromonas hydrophila, a Gram-negative bacterium, is ubiquitously found in many aquatic habitats, causing septicemia in humans and fishes. Attributed to abuse or misuse of conventional antimicrobial drug usage, antimicrobial resistance is at an alarming rise. There is an available alternative strategy to bacterial resistance to antimicrobials, which is inhibition of virulence and pathogenicity employing quorum sensing inhibitors (QSIs). Hence, actinomycin D's effectiveness against A. hydrophila SHAe 115 as a QSI was investigated in decreasing virulence factors and preventing biofilm formation.

METHODS AND RESULTS

Actinomycin D, belongs to the QSI combating Pseudomonas aeruginosa PAO1 originally isolated from an entophytic actinomycete (Streptomyces cyaneochromogenes RC1) in Areca catechu L. In the present work, further investigations were carried out to assess the effect of actinomycin D at subminimal inhibitory concentrations (sub-MICs), QS-regulated virulence factors, and biofilm inhibition strategies. Intrinsic properties encompassing inhibition of the production of protease and hemolysin and subsequent activities on biofilm formation and eradication of mature biofilm were established along with weakened swimming and swarming motilities in A. hydrophila SHAe 115. In the Tenebrio molitor survival assay, actinomycin D effectively reduced the virulence and pathogenicity of A. hydrophila, resulting in elimination of mortality. However, the hydrolysate of actinomycin D, 2-hydroxy-4,6-dimethyl-3-oxo-3H-phenoxazine-1,9-dicarboxylic acid (HDPD), had lost the QSI activity in A. hydrophila.

CONCLUSIONS

Actinomycin D was proved as a viable QSI in lessening A. hydrophila's the virulence and pathogenicity, as evident from our research findings.

Two cinnamoyl hydroxamates as potential quorum sensing inhibitors against Pseudomonas aeruginosa

Introduction

Pseudomonas aeruginosa is a ubiquitous pathogen that causes various infectious diseases through the regulation of quorum sensing (QS). The strategy of interfering with the QS systems of P. aeruginosa, coupled with a reduction in the dosage of conventional antibiotics, presents a potential solution to treating infection and mitigating antibiotic resistance. In this study, seven cinnamoyl hydroxamates were synthesized to evaluate their inhibitory effects on QS of P. aeruginosa. Among these cinnamic acid derivatives, we found cinnamoyl hydroxamic acid (CHA) and 3-methoxy-cinnamoyl hydroxamic acid (MCHA) were the two most effective candidates. Furtherly, the effect of CHA and MCHA on the production of virulence factors and biofilm of P. aeruginosa were evaluated. Ultimately, our study may offer promising potential for treating P. aeruginosa infections and reducing its virulence.

Methods

The disc diffusion test were conducted to evaluate inhibitory effects on QS of seven cinnamoyl hydroxamates. The influence of CHA and MCHA on the production of virulence and flagellar motility of P. aeruginosa was furtherly explored. Scanning electron microscopy (SEM) experiment were conducted to evaluate the suppression of CHA and MCHA on the formed biofilm of P. aeruginosa. RT-qPCR was used to detect rhlI, lasA, lasB, rhlA, rhlB, and oprL genes in P. aeruginosa. In silico docking study was performed to explore the molecular mechanism of CHA and MCHA. The synergistic effects of CHA with gentamicin were detected on biofilm cell dispersal.

Result

After treatment of CHA or MCHA, the production of multiple virulence factors, including pyocyanin, proteases, rhamnolipid, and siderophore, and swimming and swarming motilities in P. aeruginosa were inhibited significantly. And our results showed CHA and MCHA could eliminate the formed biofilm of P. aeruginosa. RT-qPCR revealed that CHA and MCHA inhibited the expression of QS related genes in P. aeruginosa. Molecular docking indicated that CHA and MCHA primarily inhibited the RhlI/R system in P. aeruginosa by competing with the cognate signaling molecule C4-HSL.Additionally, CHA exhibited potent synergistic effects with gentamicin on biofilm cell dispersal.

Discussion

P. aeruginosa is one of the most clinically and epidemiologically important bacteria and a primary cause of catheter-related urinary tract infections and ventilator-associated pneumonia. This study aims to explore whether cinnamoyl hydroxamates have inhibitory effects on QS. And our results indicate that CHA and MCHA, as two novel QSIs, offer promising potential for treating P. aeruginosa infections and reducing its virulence.

A Systematic Hierarchical Virtual Screening Model for RhlR Inhibitors Based on PCA, Pharmacophore, Docking, and Molecular Dynamics

RhlR plays a key role in the quorum sensing of Pseudomonas aeruginosa. The current structure-activity relationship (SAR) studies of RhlR inhibitors mainly focus on elucidating the functional groups. Based on a systematic review of previous research on RhlR inhibitors, this study aims to establish a systematic, hierarchical screening model for RhlR inhibitors. We initially established a database and utilized principal component analysis (PCA) to categorize the inhibitors into two classes. Based on the training set, pharmacophore models were established to elucidate the structural characteristics of ligands. Subsequently, molecular docking, molecular dynamics simulations, and the calculation of binding free energy and strain energy were performed to validate the crucial interactions between ligands and receptors. Then, the screening criteria for RhlR inhibitors were established hierarchically based on ligand structure characteristics, ligand-receptor interaction, and receptor affinity. Test sets were finally employed to validate the hierarchical virtual screening model by comparing it with the current SAR studies of RhlR inhibitors. The hierarchical screening model was confirmed to possess higher accuracy and a true positive rate, which holds promise for subsequent screening and the discovery of active RhlR inhibitors.

1H-Pyrrole-2,5-dicarboxylic acid, a quorum sensing inhibitor from one endophytic fungus in Areca catechu L., acts as antibiotic accelerant against Pseudomonas aeruginosa

Pseudomonas aeruginosa has already been stipulated as a "critical" pathogen, emphasizing the urgent need for researching and developing novel antibacterial agents due to multidrug resistance. Bacterial biofilm formation facilitates cystic fibrosis development and restricts the antibacterial potential of many current antibiotics. The capacity of P. aeruginosa to form biofilms and resist antibiotics is closely correlated with quorum sensing (QS). Bacterial QS is being contemplated as a promising target for developing novel antibacterial agents. QS inhibitors are a promising strategy for treating chronic infections. This study reported that the active compound PT22 (1H-pyrrole-2,5-dicarboxylic acid) isolated from Perenniporia tephropora FF2, one endophytic fungus from Areca catechu L., presents QS inhibitory activity against P. aeruginosa. Combined with gentamycin or piperacillin, PT22 functions as a novel antibiotic accelerant against P. aeruginosa. PT22 (0.50 mg/mL, 0.75 mg/mL, and 1.00 mg/mL) reduces the production of QS-related virulence factors, such as pyocyanin and rhamnolipid, and inhibits biofilm formation of P. aeruginosa PAO1 instead of affecting its growth. The architectural disruption of the biofilms was confirmed by visualization through scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Real-time quantitative PCR (RT-qPCR) indicated that PT22 significantly attenuated the expression of QS-related genes followed by docking analysis of molecules against QS activator proteins. PT22 dramatically increased the survival rate of Galleria mellonella. PT22 combined with gentamycin or piperacillin presents significant inhibition of biofilm formation and eradication of mature biofilm compared to monotherapy, which was also confirmed by visualization through SEM and CLSM. After being treated with PT22 combined with gentamycin or piperacillin, the survival rates of G. mellonella were significantly increased compared to those of monotherapy. PT22 significantly enhanced the susceptibility of gentamycin and piperacillin against P. aeruginosa PAO1. Our results suggest that PT22 from P. tephropora FF2 as a potent QS inhibitor is a candidate antibiotic accelerant to combat the antibiotic resistance of P. aeruginosa.

Veratryl Alcohol Attenuates the Virulence and Pathogenicity of Pseudomonas aeruginosa Mainly via Targeting las Quorum-Sensing System

Pseudomonas aeruginosa is an opportunistic pathogen that usually causes chronic infections and even death in patients. The treatment of P. aeruginosa infection has become more challenging due to the prevalence of antibiotic resistance and the slow pace of new antibiotic development. Therefore, it is essential to explore non-antibiotic methods. A new strategy involves screening for drugs that target the quorum-sensing (QS) system. The QS system regulates the infection and drug resistance in P. aeruginosa. In this study, veratryl alcohol (VA) was found as an effective QS inhibitor (QSI). It effectively suppressed the expression of QS-related genes and the subsequent production of virulence factors under the control of QS including elastase, protease, pyocyanin and rhamnolipid at sub-inhibitory concentrations. In addition, motility activity and biofilm formation, which were correlated with the infection of P. aeruginosa, were also suppressed by VA. In vivo experiments demonstrated that VA could weaken the pathogenicity of P. aeruginosa in Chinese cabbage, Drosophila melanogaster, and Caenorhabditis elegans infection models. Molecular docking, combined with QS quintuple mutant infection analysis, identified that the mechanism of VA could target the LasR protein of the las system mainly. Moreover, VA increased the susceptibility of P. aeruginosa to conventional antibiotics of tobramycin, kanamycin and gentamicin. The results firstly demonstrate that VA is a promising QSI to treat infections caused by P. aeruginosa.

Assessing the antibacterial potential of 6-gingerol: Combined experimental and computational approaches

The rise of antibiotic resistance in bacteria is becoming a global concern, particularly due to the dwindling supply of new antibiotics. This situation mandates the discovery of new antimicrobial candidates. Plant-derived natural compounds have historically played a crucial role in the development of antibiotics, serving as a rich source of substances possessing antimicrobial properties. Numerous studies have supported the reputation of 6-gingerol, a prominent compound found in the ginger family, for its antibacterial properties. In this study, the antibacterial activities of 6-gingerol were evaluated against Gram-negative bacteria, Acinetobacter baumannii and Klebsiella pneumoniae, with a particular focus on the clinically significant Gram-negative Pseudomonas aeruginosa and Gram-positive bacteria Staphylococcus aureus. Furthermore, the anti-virulence activities were assessed in vitro, in vivo, and in silico. The current findings showed that 6-gingerol's antibacterial activity is due to its significant effect on the disruption of the bacterial cell membrane and efflux pumps, as it significantly decreased the efflux and disrupted the cell membrane of S. aureus and P. aeruginosa. Furthermore, 6-gingerol significantly decreased the biofilm formation and production of virulence factors in S. aureus and P. aeruginosa in concentrations below MICs. The anti-virulence properties of 6-gingerol could be attributed to its capacity to disrupt bacterial virulence-regulating systems; quorum sensing (QS). 6-Gingerol was found to interact with QS receptors and downregulate the genes responsible for QS. In addition, molecular docking, and molecular dynamics (MD) simulation results indicated that 6-gingerol showed a comparable binding affinity to the co-crystalized ligands of different P. aeruginosa QS targets as well as stable interactions during 100 ns MD simulations. These findings suggest that 6-gingerol holds promise as an anti-virulence agent that can be combined with antibiotics for the treatment of severe infections.

Research Progress on the Combination of Quorum-Sensing Inhibitors and Antibiotics against Bacterial Resistance

Bacterial virulence factors and biofilm development can be controlled by the quorum-sensing (QS) system, which is also intimately linked to antibiotic resistance in bacteria. In previous studies, many researchers found that quorum-sensing inhibitors (QSIs) can affect the development of bacterial biofilms and prevent the synthesis of many virulence factors. However, QSIs alone have a limited ability to suppress bacteria. Fortunately, when QSIs are combined with antibiotics, they have a better therapeutic effect, and it has even been demonstrated that the two together have a synergistic antibacterial effect, which not only ensures bactericidal efficiency but also avoids the resistance caused by excessive use of antibiotics. In addition, some progress has been made through in vivo studies on the combination of QSIs and antibiotics. This article mainly expounds on the specific effect of QSIs combined with antibiotics on bacteria and the combined antibacterial mechanism of some QSIs and antibiotics. These studies will provide new strategies and means for the clinical treatment of bacterial infections in the future.

Endophytes: a uniquely tailored source of potential antibiotic adjuvants

Multidrug microbial resistance is risking an annual loss of more than 10 million people' lives by 2050. Solutions include the rational use of antibiotics and the use of drugs that reduce resistance or completely obliterate them. Here endophytes come to play due to their high-yield production and inherent nature to produce antimicrobial molecules. Around 40%, 45% and 17% of antibacterial agents were obtained from fungi, actinomycetes, and bacteria, respectively, whose secondary metabolites revealed effectiveness against resistant microbes such as MRSA, MRSE, and Shigella flexneri. Endophyte's role was not confined to bactericidal effect but extended to other mechanisms against MDR microbes, among which was the adjuvant role or the "magic bullets". Scarce focus was given to antibiotic adjuvants, and many laboratories today just screen for the antimicrobial activity without considering combinations with traditional antibiotics, which means real loss of promising resistance combating molecules. While some examples of synthetic adjuvants were introduced in the last decade, the number is still far from covering the disused antibiotics and restoring them back to clinical use. The data compiled in this article demonstrated the significance of quorum sensing as a foreseen mechanism for adjuvants from endophytes secondary metabolites, which call for urgent in-depth studies of their molecular mechanisms. This review, comprehensively and for the first time, sheds light on the significance of endophytes secondary metabolites in solving AMR problem as AB adjuvants.

An Investigation of Quorum Sensing Inhibitors against Bacillus cereus in The Endophytic Fungus Pithomyces sacchari of the Laurencia sp

Bacillus cereus, a common food-borne pathogen, forms biofilms and generates virulence factors through a quorum sensing (QS) mechanism. In this study, six compounds (dankasterone A, demethylincisterol A3, zinnimidine, cyclo-(L-Val-L-Pro), cyclo-(L-Ile-L-Pro), and cyclo-(L-Leu-L-Pro)) were isolated from the endophytic fungus Pithomyces sacchari of the Laurencia sp. in the South China Sea. Among them, demethylincisterol A3, a sterol derivative, exhibited strong QS inhibitory activity against B. cereus. The QS inhibitory activity of demethylincisterol A3 was evaluated through experiments. The minimum inhibitory concentration (MIC) of demethylincisterol A3 against B. cereus was 6.25 μg/mL. At sub-MIC concentrations, it significantly decreased biofilm formation, hindered mobility, and diminished the production of protease and hemolysin activity. Moreover, RT-qPCR results demonstrated that demethylincisterol A3 markedly inhibited the expression of QS-related genes (plcR and papR) in B. cereus. The exposure to demethylincisterol A3 resulted in the downregulation of genes (comER, tasA, rpoN, sinR, codY, nheA, hblD, and cytK) associated with biofilm formation, mobility, and virulence factors. Hence, demethylincisterol A3 is a potentially effective compound in the pipeline of innovative antimicrobial therapies.

Methyl gallate isolated from partridge tea (Mallotus oblongifolius (Miq.) Müll.Arg.) inhibits the biofilms and virulence factors of Burkholderia thailandensis

ETHNOPHARMCOLOGICAL RELEVANCE

The formation of biofilms is a factor leading to chronic infection and drug resistance in melioidosis. The production of biofilm formation and many virulence factors are regulated by quorum sensing (QS). Therefore, the discovery of QS inhibitors to reduce antibiotic abuse has attracted a lot of attention. In this case, the methanol extract of a unique ethnic medicinal plant partridge tea (Mallotus oblongifolius (Miq.) Müll.Arg.) and its isolated active compound were used as biofilms and QS inhibitors against Burkholderia thailandensis.

AIM OF THE STUDY

The purpose of this study is to investigate the anti-biofilm and anti-QS effect of the ethnic medicinal plant partridge tea and its active compounds against B. thailandensis.

METHODS

Active compound was isolated using classical phytochemical separation techniques under activity tracking. The biofilm and virulence factors (Proteases, lipases, rhamnolipids, and motility) of B. thailandensis were used to evaluate the activity of crude extracts and isolated compounds.

RESULTS

In this study, the extract of partridge tea and MG had good QS inhibitors activity against B. thailandensis E264. MG was investigated to inhibit QS-related virulence factors and the biofilm formation against B. thailandensis E264. The lipase activity of B. thailandensis E264 decreased by 49.41% at 150 μg/mL. At 75 μg/mL and 150 μg/mL, the erasion of mature biofilms reached 28.18% and 70.87%, respectively. Correspondingly, 150 μg/mL MG could significantly decrease btaR1 and btaR3 by 55.78% and 56.24%, respectively. Contradictorily, the rhamnolipid production of B. thailandensis E264 was 1.67 folds that of the control group at 150 μg/mL MG.

CONCLUSION

Through molecular docking analysis and biological phenotype data, we speculate that MG may inhibit the biofilms and virulence factors of B. thailandensis E264 by interfering two QS systems, BtaI1/R1 and BtaI3/R3. Therefore, MG should be one potential QSI for the treatment of Burkholderia pathogens.

Anti-quorum sensing effects of batatasin III: in vitro and in silico studies

The spread of multidrug resistant bacteria has fueled the development of new antibiotics to combat bacterial infections. Disrupting the quorum sensing (QS) mechanism with biomolecules is a promising approach against bacterial infections. Plants used in Traditional Chinese Medicine (TCM) represent a valuable resource for the identification of QS inhibitors. In this study, the in vitro anti-QS activity of 50 TCM-derived phytochemicals against the biosensor Chromobacterium violaceum CV026 was tested. Among the 50 phytochemicals, 7-methoxycoumarin, flavone, batatasin III, resveratrol, psoralen, isopsoralen, and rhein inhibited violacein production and showed good QS inhibitory effects. Batatasin III was selected as the best QS inhibitor based on drug-likeness, physicochemical properties, toxicity, and bioactivity score prediction analyses using SwissADME, PreADMET, ProtoxII, and Molinspiration. At 30 μg/ mL, Batatasin III inhibited violacein production and biofilm formation in C. violaceum CV026 by more than 69% and 54% respectively without affecting bacterial growth. The in vitro cytotoxicity evaluation by MTT assay demonstrated that batatasin III reduced the viability of 3T3 mouse fibroblast cells to 60% at 100 μg/mL. Furthermore, molecular docking studies showed that batatasin III has strong binding interactions with the QS-associated proteins CViR, LasR, RhlR, PqsE, and PqsR. Molecular dynamic simulation studies showed that batatasin III has strong binding interactions with 3QP1, a structural variant of CViR protein. The binding free energy value of batatasin III-3QP1 complex was -146.295 ± 10.800 KJ/mol. Overall results suggested that batatasin III could serve as a lead molecule that could be developed into a potent QS inhibitor.Communicated by Ramaswamy H. Sarma.

New Insights on Biological Activities, Chemical Compositions, and Classifications of Marine Actinomycetes Antifouling Agents

Biofouling is the assemblage of undesirable biological materials and macro-organisms (barnacles, mussels, etc.) on submerged surfaces, which has unfavorable impacts on the economy and maritime environments. Recently, research efforts have focused on isolating natural, eco-friendly antifouling agents to counteract the toxicities of synthetic antifouling agents. Marine actinomycetes produce a multitude of active metabolites, some of which acquire antifouling properties. These antifouling compounds have chemical structures that fall under the terpenoids, polyketides, furanones, and alkaloids chemical groups. These compounds demonstrate eminent antimicrobial vigor associated with antiquorum sensing and antibiofilm potentialities against both Gram-positive and -negative bacteria. They have also constrained larval settlements and the acetylcholinesterase enzyme, suggesting a strong anti-macrofouling activity. Despite their promising in vitro and in vivo biological activities, scaled-up production of natural antifouling agents retrieved from marine actinomycetes remains inapplicable and challenging. This might be attributed to their relatively low yield, the unreliability of in vitro tests, and the need for optimization before scaled-up manufacturing. This review will focus on some of the most recent marine actinomycete-derived antifouling agents, featuring their biological activities and chemical varieties after providing a quick overview of the disadvantages of fouling and commercially available synthetic antifouling agents. It will also offer different prospects of optimizations and analysis to scale up their industrial manufacturing for potential usage as antifouling coatings and antimicrobial and therapeutic agents.

Anti-Vibrio parahaemolyticus compounds from Streptomyces parvus based on Pan-genome and subtractive proteomics

Introduction

Vibrio parahaemolyticus is a foodborne pathogen commonly found in seafood, and drug resistance poses significant challenges to its control. This study aimed to identify novel drug targets for antibacterial drug discovery.

Methods

To identify drug targets, we performed a pan-genome analysis on 58 strains of V. parahaemolyticus genomes to obtain core genes. Subsequently, subtractive proteomics and physiochemical checks were conducted on the core proteins to identify potential therapeutic targets. Molecular docking was then employed to screen for anti-V. parahaemolyticus compounds using a in-house compound library of Streptomyces parvus, chosen based on binding energy. The anti-V. parahaemolyticus efficacy of the identified compounds was further validated through a series of experimental tests.

Results and Discussion

Pangenome analysis of 58 V. parahaemolyticus genomes revealed that there were 1,392 core genes. After Subtractive proteomics and physiochemical checks, Flagellar motor switch protein FliN was selected as a therapeutic target against V. parahaemolyticus. FliN was modeled and docked with Streptomyces parvus source compounds, and Actinomycin D was identified as a potential anti-V. parahaemolyticus agent with a strong binding energy. Experimental verification confirmed its effectiveness in killing V. parahaemolyticus and significantly inhibiting biofilm formation and motility. This study is the first to use pan-genome and subtractive proteomics to identify new antimicrobial targets for V. parahaemolyticus and to identify the anti-V. parahaemolyticus effect of Actinomycin D. These findings suggest potential avenues for the development of new antibacterial drugs to control V. parahaemolyticus infections.

Anti-Klebsiella pneumoniae activity of secondary metabolism of Achromobacter from the intestine of Periplaneta americana

BACKGROUND

Klebsiella pneumoniae is one of the main pathogens of clinical isolation and nosocomial infections, as K. pneumoniae show broad-spectrum resistance to β-lactam and carbapenem antibiotics. It is emerging clinical need for a safe and effective drug to anti-K. pneumoniae. At present, Achromobacter mainly focused on its degradation of petroleum hydrocarbons, polycyclic aromatic hydrocarbons, assisting insects to decompose, degrade heavy metals and utilize organic matter, but there were few reports on the antibacterial activity of the secondary metabolites of Achromobacter.

RESULTS

In this study, a strain WA5-4-31 from the intestinal tract of Periplaneta americana exhibited strong activity against K. Pneumoniae through preliminary screening. The strain was determined to be Achromobacter sp. through the morphological characteristics, genotyping and phylogenetic tree analysis, which is homologous to Achromobacter ruhlandii by 99%, its accession numbe in GenBank at National Center for Biotechnology Information (NCBI) is MN007235, and its deposit number was GDMCC NO.1.2520. Six compounds (Actinomycin D, Actinomycin X2, Collismycin A, Citrinin, Neoechinulin A and Cytochalasin E) were isolated and determined by activity tracking, chemical separation, nuclear magnetic resonance (NMR) and mass spectrometry (MS) analysis. Among them, Actinomycin D, Actinomycin X2, Collismycin A, Citrinin and Cytochalasin E showed a good effect on anti-K. pneumoniae, with MIC values of 16-64 µg/mL.

CONCLUSIONS

The study reported Achromobacter, which was from the intestinal tract of Periplaneta americana with the activity against K. Pneumoniae, can produce antibacterial compounds for the first time. It lays the foundation for development of secondary metabolites of insect intestinal microorganisms.

The implications of quorum sensing inhibition in bacterial antibiotic resistance- with a special focus on aquaculture

The aquaculture industry is an expanding and demanding industry and due to an increase in urbanization, with rise in income of developing countries population, it offers to provide a sustainable food supply. However, the industry is facing a number of challenges, out of which few needs to be tackled immediately to maximise the productivity. An upcoming problem is the emergence of antibiotic resistant pathogens due to the unchecked use of antibiotics in aquaculture and human clinical practices. A wide variety of aquatic pathogens such as Edwardsiella, Vibrio, and Aeromonas spp. use quorum sensing (QS) systems, a regulatory process involving cell communication via signalling molecules for the collective function of pathogens which regulates the genes expression including virulent genes. Quorum sensing results in bacterial biofilms formation, which leads to their reduced susceptibility towards antimicrobial agents. The usage of quorum sensing inhibitors (QSIs) has been proposed as an attractive strategy to tackle this problem. Due to the modulation of virulence genes expression, QSIs can be used as novel and viable approach to overcome antibiotic resistance in aquaculture. In this review, we direct our attention to the quorum sensing phenomenon and its viability as a target pathway for tackling the ever-growing problem of antimicrobial resistance in aquaculture. This review also provides a concise compilation of the currently available QSIs and investigates possible natural sources for quorum quenching.