Anti-Biofilm and Antivirulence Activities of Metabolites from Plectosphaerella cucumerina against Pseudomonas aeruginosa

Lonicera japonica protects Pelodiscus sinensis by inhibiting the biofilm formation of Aeromonas hydrophila

Aquaculture has suffered significant financial losses as a result of the infection of zoonotic Aeromonas hydrophila, which has a high level of resistance to classic antibiotics. In this study, we isolated an A. hydrophila strain B3 from diseased soft-shelled turtle (Pelodiscus sinensis), which is one of the most commercially significant freshwater farmed reptiles in East Asia, and found that A. hydrophila was its dominant pathogen. To better understand the inhibition effect and action mechanism of Chinese herbs on A. hydrophila, we conducted Chinese herbs screening and found that Lonicera japonica had a significant antibacterial effect on A. hydrophila B3. Experimental therapeutics of L. japonica on soft-shelled turtle showed that the supplement of 1% L. japonica to diet could significantly upregulate the immunity-related gene expression of soft-shelled turtle and protect soft-shelled turtle against A. hydrophila infection. Histopathological section results validated the protective effect of L. japonica. As the major effective component of L. japonica, chlorogenic acid demonstrated significant inhibitory effect on the growth of A. hydrophila with MIC at 6.4 mg/mL. The in vitro assay suggested that chlorogenic acid could inhibit the hemolysin/protease production and biofilm formation of A. hydrophila and significantly decrease the expression of quorum sensing, biofilm formation, and hemolysin-related genes in A. hydrophila. Our results showed that the Chinese herb L. japonica would be a promising candidate for the treatment of A. hydrophila infections in aquaculture, and it not only improves the immune response of aquatic animals but also inhibits the virulence factor (such as biofilm formation) expression of A. hydrophila. KEY POINTS: • A. hydrophila was the dominant pathogen of the diseased soft-shelled turtle. • L. japonica can protect soft-shelled turtle against A. hydrophila infection. • Chlorogenic acid inhibits the growth and biofilm formation of A. hydrophila.

Synthesis and study of antibiofilm and antivirulence properties of flavonol analogues generated by palladium catalyzed ligand free Suzuki-Miyaura coupling against Pseudomonas aeruginosa PAO1

The Suzuki-Miyaura coupling is one of the ubiquitous method for the carbon-carbon bond-forming reactions in organic chemistry. Its popularity is due to its ability to undergo extensive coupling reactions to generate a broad range of biaryl motifs in a straightforward manner displaying a high level of functional group tolerance. A convenient and efficient synthetic route to arylate different substituted flavonols through the Suzuki-Miyaura cross-coupling reaction has been explained in this study. The arylated products were acquired by the coupling of a variety of aryl boronic acids with flavonols under Pd(OAc)2 catalyzed reaction conditions in a ligand-free reaction strategy. Subsequently, the antibiofilm and antivirulence properties of the arylated flavonols against Pseudomonas aeruginosa PAO1 were studied thoroughly. The best ligands for quorum sensing proteins LasR, RhlR, and PqsR were identified using molecular docking study. These best fitting ligands were then studied for their impact on gene expression level of P. aeruginosa by RT-PCR towards quorum sensing genes lasB, rhlA, and pqsE. The downregulation in the gene expression with the effect of synthesized flavonols endorse the antibiofilm efficiency of the compounds.

Effects of elevated levels of intracellular nitric oxide on Pseudomonas aeruginosa biofilm in chronic skin wound and slow-killing infection models

Nitric oxide (NO), produced through the denitrification pathway, regulates biofilm dynamics through the quorum sensing system in Pseudomonas aeruginosa. NO stimulates P. aeruginosa biofilm dispersal by enhancing phosphodiesterase activity to decrease cyclic di-GMP levels. In a chronic skin wound model containing a mature biofilm, the gene expression of nirS, encoding nitrite reductase to produce NO, was low, leading to reduced intracellular NO levels. Although low-dose NO induces biofilm dispersion, it is unknown whether it influences the formation of P. aeruginosa biofilms in chronic skin wounds. In this study, a P. aeruginosa PAO1 strain with overexpressed nirS was established to investigate NO effects on P. aeruginosa biofilm formation in an ex vivo chronic skin wound model and unravel the underlying molecular mechanisms. Elevated intracellular NO levels altered the biofilm structure in the wound model by inhibiting the expression of quorum sensing-related genes, which was different from an in vitro model. In Caenorhabditis elegans as a slow-killing infection model, elevated intracellular NO levels increased worms' lifespan by 18%. Worms that fed on the nirS-overexpressed PAO1 strain for 4 h had complete tissue, whereas worms that fed on empty plasmid-containing PAO1 had biofilms on their body, causing severe damage to the head and tail. Thus, elevated intracellular NO levels can inhibit P. aeruginosa biofilm growth in chronic skin wounds and reduce pathogenicity to the host. Targeting NO is a potential approach to control biofilm growth in chronic skin wounds wherein P. aeruginosa biofilms are a persistent problem.

Trichoderma-derived emodin competes with ExpR and ExpI of Pectobacterium carotovorum subsp. carotovorum to biocontrol bacterial soft rot

BACKGROUND

Quorum sensing inhibitors (QSIs) are an emerging control tool that inhibits the quorum sensing (QS) system of pathogenic bacteria. We aimed to screen for potential QSIs in the metabolites of Trichoderma and to explore their inhibitory mechanisms.

RESULTS

We screened a strain of Trichoderma asperellum LN004, which demonstrated the ability to inhibit the color development of Chromobacterium subtsugae CV026, primarily attributed to the presence of emodin as its key QSI component. The quantitative polymerase chain reaction with reverse transcription results showed that after emodin treatment of Pectobacterium carotovorum subsp. carotovorum (Pcc), plant cell wall degrading enzyme-related synthetic genes were significantly downregulated, and the exogenous enzyme synthesis gene negative regulator (rsmA) was upregulated 3.5-fold. Docking simulations indicated that emodin could be a potential ligand for ExpI and ExpR proteins because it exhibited stronger competition than the natural ligands in Pcc. In addition, western blotting showed that emodin attenuated the degradation of n-acylhomoserine lactone on the ExpR protein and protected it. Different concentrations of emodin reduced the activity of pectinase, cellulase, and protease in Pcc by 20.81%-72.21%, 8.38%-52.73%, and 3.57%-47.50%. Lesion size in Chinese cabbages, carrots and cherry tomatoes following Pcc infestation was reduced by 10.02%-68.57%, 40.17%-88.56% and 11.36%-86.17%.

CONCLUSION

Emodin from T. asperellum LN004 as a QSI can compete to bind both ExpI and ExpR proteins, interfering with the QS of Pcc and reducing the production of virulence factors. The first molecular mechanism reveals the ability of emodin as a QSI to competitively inhibit two QS proteins simultaneously. © 2023 Society of Chemical Industry.

Furan-based Chalcone Annihilates the Multi-Drug-Resistant Pseudomonas aeruginosa and Protects Zebra Fish Against its Infection

The emergence of carbapenem-resistant Pseudomonas aeruginosa, a multi-drug-resistant bacteria, is becoming a serious public health concern. This bacterium infects immunocompromised patients and has a high fatality rate. Both naturally and synthetically produced chalcones are known to have a wide array of biological activities. The antibacterial properties of synthetically produced chalcone were studied against P. aeruginosa. In vitro, study of the compound (chalcone derivative named DKO1), also known as (2E)-1-(5-methylfuran-2-yl)-3-(4-nitrophenyl) prop-2-en-1-one, had substantial antibacterial and biofilm disruptive action. DKO1 effectively shielded against P. aeruginosa-induced inflammation, oxidative stress, lipid peroxidation, and apoptosis in zebrafish larvae. In adult zebrafish, the treatment enhanced the chances of survivability and reduced the sickness-like behaviors. Gene expression, biochemical analysis, and histopathology studies found that proinflammatory cytokines (TNF-α, IL-1β, IL-6, iNOS) were down regulated; antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) levels increased, and histoarchitecture was restored in zebrafish. The data indicate that DKO1 is an effective antibacterial agent against P. aeruginosa demonstrated both in vitro and in vivo.

Biofilm-Inhibitory Activity of Wild Mushroom Extracts against Pathogenic Bacteria

Objective

This study aims to investigate the bacterial biofilm-inhibitory effect of mushroom extracts.

Methods

Mushrooms were collected from Arabuko-Sokoke and Kakamega forests and identified using morphological and molecular approaches. Auricularia auricula-judae, Microporus xanthopus, Termitomyces umkowaani, Trametes elegans, and Trametes versicolor were extracted by chloroform, 70% ethanol, and hot water. Extracts were tested against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus (ATCC25923). Data were analyzed using SPSS ver. 20.0.

Results

Chloroform, 70% ethanol, and hot water extracts of A. auricula-judae (50 μg/mL) showed statistically significant antibiofilm activities against P. aeruginosa, E. coli, and S. aureus (p ≤ 0.05). M. xanthopus extracts (250 μg/mL) revealed significantly significant antibiofilm activities against each test bacterium (p ≤ 0.05). All extracts of T. umkowaani (250 μg/mL) exhibited statistically significant antibiofilm activities against S. aureus only (p ≤ 0.05). Chloroform extract of T. elegans (250 μg/mL) showed the best antibiofilm activity (69.75 ± 0.01%) against S. aureus. All T. versicolor extracts (250 μg/mL) indicated the best antibiofilm activities against S. aureus.

Conclusions

Being the first study of its kind to be conducted in Kenya, it added a novel concept to the body of knowledge already known about medical biotechnology research. It offers a fresh understanding of the various varieties of mushrooms found in Kenya, their potential biological function in the production of drugs, particularly those that combat drug resistance, and perhaps even a peek at their bioactive elements. Wild mushrooms, a hidden gem, might help to reopen the pipeline of new antibiotics that have been on the decline. However, further research is required to determine the potential mechanism(s) of action of the extracts that are in charge of the apparent antibiofilm activity.

Comparative assessment of phenolic composition profile and biological activities of green extract and conventional extracts of Salvia sclarea

In recent years, there have been an attempt to develop safe and environmental friendly solvents to replace conventional solvents, and use for extraction bioactive compounds from natural sources. A current investigation involved the preparation of green, methanolic, and ultrasonic extracts of S. sclarea, and compared their phenolic profiling using HPLC-DAD, antibacterial, antioxidant, and enzyme inhibition activities. The HPLC-DAD analysis revealed that Rosmarinic acid was the main content in all extracts, with Ellagic acid only present in the green extract. The green extract exhibited superior anti-biofilm activity against S. Aureus and E. Faecalis compared to the other extracts at MIC concentration. Furthermore, the green extract also displayed the highest inhibition of swarming motility in P. Aeruginosa with inhibition range 68.0 ± 2.1 (MIC) to 19.5 ± 0.6 (MIC/4). and better enzyme inhibitory activity against BChE (with IC50 = 131.6 ± 0.98 µg/mL) and AChE (with inhibition 47.00 ± 1.50%) compared to the other extracts; while, the ultrasonic extract showed strong inhibition of violacein production by C. Violaceum with a inhibition range 05.5 ± 0.1 (MIC/32) to 100 ± 0.00 (MIC), followed by the green extract with a inhibition range 15.0 ± 0.5 (MIC/8) to 100 ± 0.00 (MIC), additionally, the ultrasonic and methanoic extracts showed significant activity against urease enzyme with (IC50 = 171.6 ± 0.95 µg/mL and IC5 0 = 187.5 ± 1.32 µg/mL) respectively. Both the green and methanolic extracts showed considerable antioxidant activities, as β-carotene-linoleic acid (IC50 = 5.61 ± 0.47 µg/mL and 5.37 ± 0.27 µg/mL), DPPH· (IC50 = 19.20 ± 0.70 µg/mL and 16.31 ± 0.23 µg/mL), ABTS·+(IC50 = 8.64 ± 0.63 µg/mL and 6.50 ± 0.45 µg/mL) and CUPRAC (A0.5 = 17.22 ± 0.36 µg/mL and 12.28 ± 0.12 µg/mL) respectively, likewise the green extract performing better in metal chelating compared to the other extracts. The green extraction is reported as a cost effective and solvent free method for extracting natural products that produces compounds free of toxic chemicals. This could be the method to be used in the industries as a renewable method.

Phloretin Inhibits Quorum Sensing and Biofilm Formation in Serratia marcescens

This study investigated the antivirulence capacity and mechanism of apple-skin-derived phloretin against Serratia marcescens NJ01, a vegetable spoilage bacterium. At 0.5 to 2 mg/mL doses, phloretin considerably inhibited the secretion of acyl homoserine lactones (AHLs), indicating that phloretin disrupted quorum sensing (QS) in S. marcescens NJ01. The dysfunction of QS resulted in reduced biofilms and the decreased production of protease, prodigiosin, extracellular polysaccharides (EPSs), and swimming and swarming motilities. Dysfunctional QS also weakened the activity of antioxidant enzymes and improved oxidative injury. The improved oxidative injury changed the composition of the membrane, improved membrane permeability, and eventually increased the susceptibility of biofilm cells to amikacin, netilmicin, and imipenem. The disrupted QS and enhanced oxidative stress also caused disorders of amino acid metabolism, energy metabolism, and nucleic acid metabolism, and ultimately attenuated the ability of S. marcescens NJ01 to induce spoilage. Our results indicated that phloretin can act as a potent drug to defend against spoilage by S. marcescens.

Alkaline phosphatase LapA regulates quorum sensing-mediated virulence and biofilm formation in Pseudomonas aeruginosa PAO1 under phosphate depletion stress

IMPORTANCE

Our previous study demonstrated that the expression of lapA was induced under phosphate depletion conditions, but its roles in virulence and biofilm formation by Pseudomonas aeruginosa remain largely unknown. This study presents a systematic investigation of the roles of lapA in virulence induction and biofilm formation by constructing a lapA-deficient strain with P. aeruginosa PAO1. The results showed that deletion of the lapA gene evidently reduced elastase activity, swimming motility, C4-HSL, and 3-oxo-C12-HSL production, and increased rhamnolipid production under phosphate depletion stress. Moreover, lapA gene deletion inhibited PAO1 biofilm formation in porcine skin explants by reducing the expression levels of las and rhl quorum sensing systems and extracellular polymeric substance synthesis. Finally, lapA gene deletion also reduced the virulence of PAO1 in Caenorhabditis elegans in fast-kill and slow-kill infection assays. This study provides insights into the roles of lapA in modulating P. aeruginosa virulence and biofilm formation under phosphate depletion stress.

Developing 3-(2-Isocyano-6-methylbenzyl)-1H-indole Derivatives to Enhance the Susceptibility of Serratia marcescens by Occluding Quorum Sensing

Quorum sensing (QS) inhibition is recognized as a novel antimicrobial target for infections caused by drug-resistant pathogens and is an attractive strategy for antipathogenic agent development. We designed and synthesized three parts of 3-(2-isocyanobenzyl)-1H-indole derivatives and tested their activity as novel quorum sensing inhibitors (QSIs). 3-(2-Isocyanobenzyl)-1H-indole derivatives demonstrated promising QS, biofilms, and prodigiosin inhibitory activities against Serratia marcescens at subminimum inhibitory concentrations (sub-MICs). In particular, 3-(2-isocyano-6-methylbenzyl)-1H-indole (IMBI, 32) was identified as the best candidate based on several screening assays, including biofilm and prodigiosin inhibition. Further studies demonstrated that exposure to IMBI at 1.56 μg/mL to S. marcescens NJ01 significantly inhibited the formation of biofilms by 42%. The IMBI treatment on S. marcescens NJ01 notably enhanced the susceptibility of the formed biofilms, destroying the architecture of the biofilms by up to 40%, as evidenced by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). For interference of virulence factors in S. marcescens NJ01, IMBI at 3.12 μg/mL inhibited the activity of protease and extracellular polysaccharides (EPS) by 17% and 51%, respectively, which were higher than that of the positive control vanillic acid (VAN). Furthermore, IMBI downregulated the expression of QS- and biofilm-related genes fimA, bsmA, pigP, flhC, rssB, fimC, and rsmA by 1.02- to 2.74-fold. To confirm these findings, molecular docking was performed, which indicated that the binding of IMBI to SmaR, RhlI, RhlR, LasR, and CviR could antagonize the expression of QS-linked traits. In addition, molecular dynamic simulations (MD) and energy calculations indicated that the binding of receptors with IMBI was extremely stable. The biofilms of S. marcescens NJ01 were markedly reduced by 50% when IMBI (0.39 μg/mL) was combined with kanamycin (0.15 μg/mL). In conclusion, this study highlights the potency of IMBI in inhibiting the virulence factors of S. marcescens. IMBI has all the potential to be developed as an effective and efficient QS inhibitor and antibiofilm agent in order to restore or improve antimicrobial drug sensitivity.

Inhibition of biofilm formation, quorum sensing and virulence factor production in Pseudomonas aeruginosa PAO1 by selected LasR inhibitors

The quorum sensing network of Pseudomonas aeruginosa mediates the regulation of genes controlling biofilm formation and virulence factors. The rise of drug resistance to Pseudomonas aeruginosa infections has made quorum sensing-regulated biofilm formation in clinical settings a major issue. In the present study, LasR inhibitors identified in our previous study were evaluated for their antibiofilm and antiquorum sensing activities against P. aeruginosa PAO1. The compounds selected were (3-[2-(3,4-dimethoxyphenyl)-2-(1H-indol-3-yl)ethyl]-1-(2-fluorophenyl)urea) (C1), (3-(4-fluorophenyl)-2-[(3-methylquinoxalin-2-yl)methylsulfanyl]quinazolin-4-one) (C2) and (2-({4-[4-(2-methoxyphenyl)piperazin-1-yl]pyrimidin-2-yl}sulfanyl)-N-(2,4,6-trimethylphenyl)acetamide) (C3). The minimum inhibitory concentrations of C1 and C2 were 1000 μM, whereas that of C3 was 500 μM. At sub-MICs, the compounds showed potent antibiofilm activity without affecting the growth of P. aeruginosa PAO1. Electron microscopy confirmed the disruption of biofilm by the selected compounds. The antiquorum sensing activity of the compounds was revealed by the inhibition of violacein in Chromobacterium violaceum and the inhibition of swimming and swarming motilities in P. aeruginosa PAO1. Furthermore, the compounds also attenuated the production of quorum sensing-mediated virulence factors. The qRT-PCR revealed the downregulation of quorum sensing regulatory genes, namely lasI, lasR, rhlI, rhlR, lasB, pqsA and pqsR. The selected compounds also exhibited lower cytotoxicity against peripheral blood lymphocytes. Thus, this study could pave a way to explore these compounds for the development of therapeutic agent against Pseudomonas aeruginosa biofilm-related infections.

Analysis of Antibiofilm Activities of Bioactive Compounds from Honeyweed (Leonurus sibiricus) Against P. aeruginosa: an In Vitro and In Silico Approach

Leonurus sibiricus (Red verticilla, honeyweed) is a type of herbaceous plant predominantly found in Asian subcontinents as weed in crop fields and is widely used for treating diabetes, bronchitis, and menstrual irregularities. However, there is a dearth of study in the application of the plant phytocompounds for treating biofilm-associated chronic infections. The bioactive compounds mainly comprise of tri-terpenes, di-terpenes, phenolic acid, and flavonoids which may have potential role as antimicrobial and antibiofilm agents. Acute and chronic infection causing microbes usually form biofilm and develop virulence factors and antibiotic resistance through quorum sensing (QS). In this study, the bioactive compounds leosibirin, sibiricinone A, leosibirone A, leonotin, quercetin, lavandulifolioside, and myricetin were identified using GC-MS analysis. These were used for analyzing the antibiofilm and anti-quorum sensing activities (rhamnolipid, AHL assay, swarming motility assay) against the biofilm formed by Pseudomonas aeruginosa, the most significant nosocomial disease-causing bacteria. The compounds were able to bring about maximum inhibition in biofilm formation and QS. Although the antibiofilm activity of the phytoextract was found to be higher than that of individual phytocompounds at a concentration of 250 µg/mL, quercetin and myricetin showed highest antibiofilm activity against Pseudomonas aeruginosa, respectively, at MIC values of 135 µg/mL and 150 µg/mL against P aeruginosa. FT-IR study also revealed that the active ingredients were able to bring about the destruction of exopolysaccharides (EPS). These observations were further validated by molecular docking interactions that showed the active ingredients inhibit the functioning of QS sensing proteins by binding with them. It was observed that myricetin showed better interactions with the QS proteins of P. aeruginosa. Myricetin and quercetin show considerable inhibition of biofilm in comparison to the phytocompounds. Thus, the present study suggests that the active compounds from L. sibiricus can be used as an alternate strategy in inhibiting the biofilm formed by pathogenic organisms.

Microbial Biofilm: A Review on Formation, Infection, Antibiotic Resistance, Control Measures, and Innovative Treatment

Biofilm is complex and consists of bacterial colonies that reside in an exopolysaccharide matrix that attaches to foreign surfaces in a living organism. Biofilm frequently leads to nosocomial, chronic infections in clinical settings. Since the bacteria in the biofilm have developed antibiotic resistance, using antibiotics alone to treat infections brought on by biofilm is ineffective. This review provides a succinct summary of the theories behind the composition of, formation of, and drug-resistant infections attributed to biofilm and cutting-edge curative approaches to counteract and treat biofilm. The high frequency of medical device-induced infections due to biofilm warrants the application of innovative technologies to manage the complexities presented by biofilm.

Evaluating Biofilm Inhibitory Potential in Fish Pathogen, Aeromonas hydrophila by Agricultural Waste Extracts and Assessment of Aerolysin Inhibitors Using In Silico Approach

Aeromonas hydrophila, an opportunistic bacteria, causes several devastating diseases in humans and animals, particularly aquatic species. Antibiotics have been constrained by the rise of antibiotic resistance caused by drug overuse. Therefore, new strategies are required to prevent appropriate antibiotic inability from antibiotic-resistant strains. Aerolysin is essential for A. hydrophila pathogenesis and has been proposed as a potential target for inventing drugs with anti-virulence properties. It is a unique method of disease prevention in fish to block the quorum-sensing mechanism of A. hydrophila. In SEM analysis, the crude solvent extracts of both groundnut shells and black gram pods exhibited a reduction of aerolysin formation and biofilm matrix formation by blocking the QS in A. hydrophila. Morphological changes were identified in the extracts treated bacterial cells. Furthermore, in previous studies, 34 ligands were identified with potential antibacterial metabolites from agricultural wastes, groundnut shells, and black gram pods using a literature survey. Twelve potent metabolites showed interactions between aerolysin and metabolites during molecular docking analysis, in that H-Pyran-4-one-2,3 dihydro-3,5 dihydroxy-6-methyl (-5.3 kcal/mol) and 2-Hexyldecanoic acid (-5.2 kcal/mol) showed promising results with potential hydrogen bond interactions with aerolysin. These metabolites showed a better binding affinity with aerolysin for 100 ns in molecular simulation dynamics. These findings point to a novel strategy for developing drugs using metabolites from agricultural wastes that may be feasible pharmacological solutions for treating A. hydrophila infections for the betterment of aquaculture.

Metal, metal oxide and polymeric nanoformulations for the inhibition of bacterial quorum sensing

Antibiotic resistance of bacteria has caused a significant public health challenge and economic problem, resulting in a necessity to find efficient antibacterial agents. Conventional bactericidal agents hinder the growth of bacteria by slowing down the cell wall synthesis or disturbing bacterial DNA replication, protein production or other bacterial cellular metabolism that can augment natural selection pressure for turning up new antibiotic-resistant strains. Virulence properties and biofilm formation of bacteria are orchestrated by quorum-sensing systems. These quorum-sensing systems normally control antimicrobial production; and targeting these systems using metal-based nanoparticles or polymeric nanoparticles can be considered as powerful antibacterial treatments owing to their specific physicochemical and therapeutic properties. In this review, recent advances and challenges related to the inactivation of quorum-sensing systems by these nanoparticles are presented to obtain comprehensive viewpoints for future studies.

Genomic and phenotypic biology of a novel Dickeya zeae WH1 isolated from rice in China: Insights into pathogenicity and virulence factors

Soft rot caused by Dickeya zeae is an important bacterial disease affecting rice and other plants worldwide. In this study, Nanopore and Illumina sequencing platforms were used to sequence the high-quality complete genome of a novel D. zeae strain WH1 (size: 4.68 Mb; depth: 322.37x for Nanopore, 243.51x for Illumina; GC content: 53.59%), which was isolated from healthy rice root surface together with Paenibacillus polymyxa, a potential biocontrol bacterium against D. zeae strain WH1. However, the pure WH1 culture presented severe pathogenicity. Multilocus sequence analysis (MLSA) indicated that strains WH1, EC1, and EC2 isolated from rice were grouped into a clade differentiated from other D. zeae strains. The average nucleotide identity (ANI) and DNA-DNA hybridization (DDH) analyses demonstrated that WH1 was phylogenetically closest to EC2. Furthermore, the pathogenicity determinants and virulence factors of WH1 were mainly analyzed through genomic comparison with complete genomes of other D. zeae strains with high virulence (EC1, EC2, MS1, and MS2). The results revealed that plant cell wall-degrading extracellular enzymes (PCWDEs), flagellar and chemotaxis, and quorum sensing were highly conserved in all analyzed genomes, which were confirmed through phenotypic assays. Besides, WH1 harbored type I, II, III, and VI secretion systems (T1SS, T2SS, T3SS, and T6SS), but lost T4SS and T5SS. Like strains MS1 and MS2 isolated from bananas, WH1 harbored genes encoding both capsule polysaccharide (CPS) and exopolysaccharide (EPS) biosynthesis. The results of pathogenicity assays demonstrated that WH1 produced severe soft rot symptoms on potato tubers, carrots, radishes, and Chinese cabbage. Meanwhile, WH1 also produced phytotoxin(s) to inhibit rice seed germination with an 87% inhibitory rate in laboratory conditions. More importantly, we confirmed that phytotoxin(s) produced by WH1 are different from zeamines produced by EC1. Comparative genomics analyses and phenotypic and pathogenicity assays suggested that WH1 likely evolved through a pathway different from the other D. zeae strains from rice, producing a new type of rice foot rot pathogen. These findings highlight the emergence of a new type of D. zeae strain with high virulence, causing soft rot in rice and other plants.

3-Phenylpropan-1-Amine Enhanced Susceptibility of Serratia marcescens to Ofloxacin by Occluding Quorum Sensing

Serratia marcescens (S. marcescens) is an environmental bacterium that causes infections with high morbidity and mortality. Notably, infections caused by multidrug-resistant S. marcescens have become a global public health issue. Therefore, the discovery of promising compounds to reduce the virulence of pathogens and restore antibiotic activity against multidrug-resistant bacteria is critical. Quorum sensing (QS) regulates virulence factors and biofilm formation of microorganisms to increase their pathogenicity and is, therefore, an important factor in the formation of multidrug resistance. In this study, we found that 3-phenylpropan-1-amine (3-PPA) inhibited S. marcescens NJ01 biofilm formation and virulence factors, including prodigiosin, protease, lipase, hemolysin, and swimming. The combination of 3-PPA (50.0 μg/mL) and ofloxacin (0.2 μg/mL) enhanced S. marcescens NJ01 sensitivity to ofloxacin. Based on crystalline violet staining, scanning electron microscopy (SEM), and confocal laser scanning microscopy (CLSM), 3-PPA (50.0 μg/mL) reduced S. marcescens NJ01 biofilm formation by 48%. Quantitative real-time PCR (qRT-PCR) showed that 3-PPA regulated the expression of virulence- and biofilm-related genes fimA, fimC, bsmB, pigP, flhC, flhD, and sodB. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) indicated that 3-PPA affected intracellular metabolites of S. marcescens NJ01, leading to reduce metabolic activity. These results suggested that 3-PPA inhibits the pathogenicity of S. marcescens NJ01 by occluding QS. Thus, 3-PPA is feasible as an ofloxacin adjuvant to overcome multidrug-resistant S. marcescens and improve the treatment of intractable infections. IMPORTANCE Multidrug-resistant bacteria have become a major threat to global public health, leading to increased morbidity, mortality, and health care costs. Bacterial virulence factors and biofilms, which are regulated by quorum sensing (QS), are the primary causes of multidrug resistance. In this study, 3-PPA reduced virulence factors and eliminated biofilm formation by inhibiting QS in S. marcescens NJ01 bacteria, without affecting bacterial growth, thus restoring sensitivity to ofloxacin. Thus, the discovery of compounds that can restore antibiotic activity against bacteria is a promising strategy to mitigate multidrug resistance in pathogens.

Serratiopeptidase Affects the Physiology of Pseudomonas aeruginosa Isolates from Cystic Fibrosis Patients

Pseudomonas aeruginosa is frequently involved in cystic fibrosis (CF) airway infections. Biofilm, motility, production of toxins and the invasion of host cells are different factors that increase P. aeruginosa's virulence. The sessile phenotype offers protection to bacterial cells and resistance to antimicrobials and host immune attacks. Motility also contributes to bacterial colonization of surfaces and, consequently, to biofilm formation. Furthermore, the ability to adhere is the prelude for the internalization into lung cells, a common immune evasion mechanism used by most intracellular bacteria, such as P. aeruginosa. In previous studies we evaluated the activity of metalloprotease serratiopeptidase (SPEP) in impairing virulence-related properties in Gram-positive bacteria. This work aimed to investigate SPEP's effects on different physiological aspects related to the virulence of P. aeruginosa isolated from CF patients, such as biofilm production, pyoverdine and pyocyanin production and invasion in alveolar epithelial cells. Obtained results showed that SPEP was able to impair the attachment to inert surfaces as well as adhesion/invasion of eukaryotic cells. Conversely, SPEP's effect on pyocyanin and pyoverdine production was strongly strain-dependent, with an increase and/or a decrease of their production. Moreover, SPEP seemed to increase swarming motility and staphylolytic protease production. Our results suggest that a large number of clinical strains should be studied in-depth before drawing definitive conclusions. Why different strains sometimes react in opposing ways to a specific treatment is of great interest and will be the object of future studies. Therefore, SPEP affects P. aeruginosa's physiology by differently acting on several bacterial factors related to its virulence.

Hurdle technology based on the use of microencapsulated pepsin, trypsin and carvacrol to eradicate Pseudomonas aeruginosa and Enterococcus faecalis biofilms

The biofilm lifestyle plays a major role in the resistance and virulence of Pseudomonas aeruginosa and Enterococcus faecalis. In this study, two microencapsulated proteases (pepsin ME-PEP and trypsin ME-TRYP) were evaluated for their biofilm dispersal activity and their synergistic effect with microencapsulated carvacrol (ME-CARV). Spray-drying was used to protect enzymes and essential oil and enhance their activities. Cell count analysis proved the synergistic activity of enzymes and carvacrol treatment as biofilms were further reduced after combined treatment in comparison to ME-CARV or enzymes alone. Furthermore, results showed that sequential treatment in the order ME-TRYP - ME-PEP - ME-CARV resulted in more efficient biofilm removal with a maximum reduction of 5 log CFU mL^-1 for P. aeruginosa and 4 log CFU mL^-1 for E. faecalis. This study proposes that the combination of microencapsulated proteases with ME-CARV could be useful for the effective control of P. aeruginosa and E. faecalis biofilms.

In Vitro Synergistic Inhibitory Activity of Natural Alkaloid Berberine Combined with Azithromycin against Alginate Production by Pseudomonas aeruginosa PAO1

Background. Berberine (BER) is a natural isoquinoline alkaloid which extensively been applied to treat bacterial infection in TCM for a long time. Alginate is an important component of Pseudomonas aeruginosa biofilm. Herein, we investigated the effects of berberine and azithromycin (AZM) on alginate in the biofilm of P. aeruginosa PAO1. Methods. The MIC and synergistic activity of BER and AZM against PAO1 were determined using the micro broth dilution and checkerboard titration methods, respectively. The effect of BER on PAO1 growth was evaluated using a time-kill assay. Moreover, the effects of BER, AZM, and a combination of both on PAO1 biofilm formation, kinesis, and virulence factor expression were evaluated at subinhibitory concentrations. The alginate content in the biofilm was detected using ELISA, and the relative expression of alginate formation-related genes algD, algR, and algG was detected by qRT-PCR. Results. Simultaneous administration of berberine significantly reduced the MIC of azithromycin, and berberine at a certain concentration inhibited PAO1 growth. Moreover, combined berberine and azithromycin had synergistic effects against PAO1, significantly reducing biofilm formation, swarming, and twitching motility, and the production of virulence factors. The relative expression of alginate-related regulatory genes algG, algD, and algR of the combined treatment group was significantly lower than that of the control group. Conclusion. In summary, berberine and azithromycin in combination had a significant synergistic effect on the inhibition of alginate production by P. aeruginosa. Further molecular studies are in great need to reveal the mechanisms underlying the synergistic activity between berberine and azithromycin.

2-Hydroxymethyl-1-methyl-5-nitroimidazole, one siderophore inhibitor, occludes quorum sensing in Pseudomonas aeruginosa

Siderophore is necessary for the survival of microorganisms and is interregulated with quorum sensing (QS) systems. It is related to growth, proliferation, virulence, and other bacterial social activities as a virulence factor. Thus, we speculated that the QS system could be occluded by inhibiting siderophore production. 2-Hydroxymethyl-1-methyl-5-nitroimidazole (HMMN), one siderophore inhibitor of Pseudomonas aeruginosa PAO1 (P. aeruginosa PAO1), was obtained by using the Chromeazurol S (CAS) method. We found that HMMN inhibited siderophore production and influenced the biological effects of QS regulation, including biofilm formation and pyocyanin production. HMMN (150 μg/ml) inhibited the siderophore production of P. aeruginosa PAO1 by 69.37%. In addition, HMMN could inhibit pyocyanin production and biofilm formation and erase the formed biofilm of P. aeruginosa PAO1. HMMN (150 μg/ml) inhibited the biofilm formation of P. aeruginosa PAO1 by 28.24%. The erasure rate of the formed biofilm reached 17.03%. Furthermore, HMMN (150 μg/ml) inhibited P. aeruginosa PAO1 pyocyanin production by 36.06%. Meanwhile, positive-control hordenine (500.0 μg/ml) reduced the biofilm formation and pyocyanin production of P. aeruginosa PAO1 by 14.42% and 34.35%, respectively. The erasure rate of hordenine to the formed biofilm is 11.05% at 500 μg/ml. Quantitative real-time polymerase chain reaction (qRT-PCR) showed that HMMN downregulates not only siderophore-related genes but also QS-related genes, as well as hordenine. These results suggest that a siderophore inhibitor could be used as a QS inhibitor to occlude the QS system and reduce virulence.

Virulence and Biofilm Inhibition of 3-Methoxycinnamic Acid against Agrobacterium tumefaciens

AIMS

In the current study the anti-virulence and anti-biofilm activities of the cinnamic acid derivative, 3-methoxycinnamic acid, was investigated against Agrobacterium tumefaciens.

METHODS AND RESULTS

Based on the disc diffusion test and β-galactosidase activity assay, 3-methoxycinnamic acid was shown to interfere with the quorum sensing (QS) system of A. tumefaciens. Crystal violet staining assay, phenol-sulfuric acid method, Bradford protein assay and confocal laser scanning microscopy (CLSM) revealed that the biofilm formation of A. tumefaciens was inhibited after the treatment of 3-methoxycinnamic acid. Employing high performance liquid chromatography (HPLC) analysis of culture supernatant revealed that the production of 3-oxo-octanoylhomoserine lactone (3-oxo-C8-HSL) decreased concentration-dependently after treatment with 3-methoxycinnamic acid. Swimming and chemotaxis assays also indicated that 3-methoxycinnamic acid had a good effect on reducing the motility and chemotaxis of A. tumefaciens. In addition, the RT-qPCR, molecular docking and simulations further demonstrated that 3-methoxycinnamic acid could competitively inhibit the binding of 3-oxo-C8-HSL to TraR and down-regulate virulence-related genes.

CONCLUSIONS

3-Methoxycinnamic acid is proved to have good anti-virulence and anti-biofilm activities against A. tumefaciens.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first study that investigates the anti-virulence and anti-biofilm activities of 3-methoxycinnamic acid against A. tumefaciens. With its potential QS-related virulence and biofilm inhibitory activities, 3-methoxycinnamic acid is expected to be developed as a potent pesticide or adjuvant for the prevention and treatment of crown gall caused by A. tumefaciens.

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

The infections caused by Pseudomonas aeruginosa are difficult to treat due to its multidrug resistance. A promising strategy for controlling P. aeruginosa infection is targeting the quorum sensing (QS) system. Actinomycin D isolated from the metabolite of endophyte Streptomyces cyaneochromogenes RC1 exhibited good anti-QS activity against P. aeruginosa PAO1. Actinomycin D (50, 100, and 200 μg/mL) significantly inhibited the motility as well as reduced the production of multiple virulence factors including pyocyanin, protease, rhamnolipid, and siderophores. The images of confocal laser scanning microscopy and scanning electron microscopy revealed that the treatment of actinomycin D resulted in a looser and flatter biofilm structure. Real-time quantitative PCR analysis showed that the expression of QS-related genes lasI, rhlI, rhlR, pqsR, pslA, and pilA were downregulated dramatically. The production of QS signaling molecules N-(3-oxododecanoyl)-L-homoserine lactone and N-butanoyl-L-homoserine lactone were also decreased by actinomycin D. These findings suggest that actinomycin D, a potent in vitro anti-virulence agent, is a promising candidate to treat P. aeruginosa infection by interfering with the QS systems.

A Cyclic Disulfide Diastereomer From Bioactive Fraction of Bruguiera gymnorhiza Shows Anti-Pseudomonas aeruginosa Activity

Pseudomonas aeruginosa is an opportunistic pathogen that commonly causes hospital-acquired infection and is of great concern in immunocompromised patients. The quorum sensing (QS) mechanism of P. aeruginosa is well studied and known to be responsible for pathogenicity and virulence. The QS inhibitor derived from the natural product can be an important therapeutic agent for pathogen control. The present study reports the role of Bruguiera gymnorhiza purified fraction (BG138) in inhibiting virulence factor production, biofilm formation, quorum sensing molecules, and expression of QS-related genes of P. aeruginosa. Structural characterization of BG138 by high resolution mass spectrometry, Fourier transform infrared spectroscopy, 1D (¹H and ¹³C NMR) and 2D NMR reveals that the fraction is a mixture of already known cyclic disulfide diastereomer, namely, brugierol and isobrugierol. The minimum inhibitory concentration (MIC) of BG138 against P. aeruginosa was 32 μg/ml. Biofilm formation was significantly reduced at sub-MIC concentrations of BG138. Scanning electron microscopy analysis reports the concentration-dependent biofilm inhibition and morphological changes of P. aeruginosa. Flow cytometry–based cell viability assay showed that P. aeruginosa cells exhibit increased propidium iodide uptake on treatment with 32 and 64 μg/ml of BG138. At sub-MIC concentrations, BG138 exhibited significant inhibition of virulence factors and reduced swimming and swarming motility of P. aeruginosa. Furthermore, the effect of BG138 on the expression of QS-related genes was investigated by qRT-PCR. Taken together, our study reports the isolation and structural characterization of bioactive fraction BG138 from B. gymnorhiza and its anti-biofilm, anti-virulence, anti-quorum sensing, and cell-damaging activities against P. aeruginosa.

The activity of Meniran (Phyllanthus niruri Linn.) extract on Salmonella pullorum infected broilers

Background and Aim: Pullorum is an acute and chronic disease caused by Salmonella pullorum, often infecting chicken farms. Pullorum disease treatment using antibiotics that do not follow the control dose can cause bacteria to become antibiotic-resistant. Meniran contributes to inhibiting and antagonizing bacteria and can increase the efficiency of chicken feed because of its bioactive compounds, including alkaloids, flavonoids, tannins, and saponins. This study aimed to determine the activity of Meniran extract (Phyllanthus niruri Linn.) in broilers infected with S. pullorum. Materials and Methods: In vitro study that was conducted includes phytochemical test, diffusion, and dilution methods using Meniran extract at 5%, 10%, 20%, and 40% concentrations and tylosin at 2% concentration. The data of the dilution method (minimum inhibitory concentration [MIC] and minimum bactericidal concentration [MBC]) were processed using probit analysis to determine LC50. In vivo study was conducted by randomly dividing 20 broilers into five treatment groups, four per group. The chickens (except in group P0–) were infected with S. pullorum aged 14 days. Then, the treatment was conducted according to the divided groups when the chickens were aged 21-34 days. The said treatments are P0– (uninfected S. pullorum and unadministered with Meniran extract), P0+ (infected with S. pullorum and unadministered with Meniran extract), and P1, P2, and P3 (infected with S. pullorum and administered with Meniran extract with 5%, 10%, and 20% concentrations, respectively). Data from the phytochemical test were analyzed as descriptive. The data from the diffusion method were analyzed using one-way analysis of variance (ANOVA) and Duncan's test. Then, the results of broilers' performance were analyzed using ANOVA and Duncan's test. Results: The phytochemical test showed positive for alkaloid, tannin, saponin, flavonoid, and steroid/triterpenoid. The diffusion method formed the largest zone at 40% concentration with 15.6 mm, while 20%, 10%, and 5% had average of 13.15 mm, 8.38 mm, and 5.8 mm, respectively. The dilution method (MIC and MBC) exhibited the antibacterial ability of Meniran extract against S. pullorum at 20% dose and LC50 14.118% concentration. The Meniran extract administration in broilers exhibited improved performance of chickens infected with S. pullorum, with the administration of 20% dose of Meniran extract showing the best result. Conclusion: About 20% concentration Meniran extract can serve as an antibacterial agent and showed the best results in broilers infected with S. pullorum.

New Sesquiterpenoids From Plant-Associated Irpex lacteus

Bacteria produce a large number of virulence factors through the quorum sensing (QS) mechanism. Inhibiting such QS system of the pathogens without disturbing their growth is a potential strategy to control multi-drug-resistant pathogens. To accomplish this, two new tremulane-type sesquiterpenoids, irpexolaceus H (1) and I (2), along with two known furan compounds, irpexlacte B (3) and C (4), were isolated from Orychophragmus violaceus (L.) OE Schulz endophytic fungus Irpex lacteus (Fr.) Fr. Their structures were elucidated by detailed spectroscopic data (NMR, HRESIMS, IR, and UV), single-crystal X-ray diffraction, and electronic circular dichroism (ECD) analysis. Furthermore, those compounds were evaluated for anti-quorum sensing (anti-QS) activity, and compound 3 was found contributing to the potential QS inhibitory activity.

Inhibition of Quorum-Sensing Regulator from Pseudomonas aeruginosa Using a Flavone Derivative

Quorum sensing (QS) is a cell-to-cell communication process that controls bacterial collective behaviors. The QS network regulates and coordinates bacterial virulence factor expression, antibiotic resistance and biofilm formation. Therefore, inhibition of the QS system is an effective strategy to suppress the bacterial virulence. Herein, we identify a phosphate ester derivative of chrysin as a potent QS inhibitor of the human pathogen Pseudomonas aeruginosa (P. aeruginosa) using a designed luciferase reporter assay. In vitro biochemical analysis shows that the chrysin derivative binds to the bacterial QS regulator LasR and abrogates its DNA-binding capability. In particular, the derivative exhibits higher anti-virulence activity compared to the parent molecule. All the results reveal the potential application of flavone derivative as an anti-virulence compound to combat the infectious diseases caused by P. aeruginosa.

Quorum Sensing Inhibition and Metabolic Intervention of 4-Hydroxycinnamic Acid Against Agrobacterium tumefaciens

The natural product 4-hydroxycinnamic acid (HA) was firstly isolated from the metabolites of Phomopsis liquidambari, one endophytic fungus from Punica granatum leaves. The anti-QS potential of HA was evaluated by β-galactosidase assay and acylated homoserine lactones (AHL) analysis. The MIC of HA was > 1.20 mM. Exposure to HA at sub-MIC concentrations (0.30-0.60 mM) remarkably reduced the β-galactosidase activity and AHL secretion. Transcriptional analysis by qRT-PCR and docking simulation indicated that HA functions as an anti-QS agent by inhibiting the transcriptional levels of traI and traR rather than signal mimicry. The blocked QS lead to suppressed biofilm formation, motilities, and flagella formation after exposure to HA at concentrations ranging from 0.30 to 0.80 mM. The dysfunctional QS also resulted in repressed antioxidant enzymes and intensified oxidative stress. The intensified oxidative stress destroyed membrane integrity, induced energy supply deficiency, resulted in disorder of protein and nuclear acid metabolism, and ultimately weakened pathogenicity of A. tumefaciens. HA may have promising potential for controlling A. tumefaciens.

Quality Related Safety Evaluation of a South African Traditional Formulation (PHELA®) as Novel Anti-Biofilm Candidate

A South African traditional formulation, PHELA^®, is consumed by the traditional people for severe chest problems with coughing, diarrhea, oral ulcers etc. The present study focused on establishing the anti-infective properties of a safe and standardized poly-herbal formulation through a series of criteria and specifications.

Sesquiterpenoids and furan derivatives from the Orychophragmus violaceus (L.) O.E. Schulz endophytic fungus Irpex lacteus OV38

Nine undescribed compounds, including six tremulane-type sesquiterpenoids, irpexolaceus A-F, one phenolic bisabolane-type sesquiterpenoid, irpexolaceus G, and two furan derivatives, irpexonjust A-B, as well as eight known analogs, were isolated from an endophytic fungus (Irpex lacteus OV38) of Orychophragmus violaceus (L.) O.E. Schulz, a Chinese medicinal and edible plant. The structures of these natural compounds were elucidated based on NMR, HRESIMS, single-crystal X-ray diffraction, and ECD spectroscopic data. Among the tested isolates (50 μg/mL), the inhibitory effects of irpexolaceus A, C, D, F, and G, irpexonjust B, and irpexlacte B against NO release from LPS-induced RAW 264.7 cells were higher than 45%, while irpexlacte C (42.6%), irpexolaceus B (39.6%), irpexonjust A (43.7%), and irpexolaceus E (33.6%) exhibited weaker inhibitory effects on the release of NO.

Anti-Virulence Properties of Coridothymus capitatus Essential Oil against Pseudomonas aeruginosa Clinical Isolates from Cystic Fibrosis Patients

Pseudomonas aeruginosa is an opportunistic pathogen responsible for nosocomial infections, and is often involved in airway infections of cystic fibrosis (CF) patients. P. aeruginosa virulence is related to its ability to form biofilm, trigger different types of motilities, and produce toxins (for example, bacterial pigments). In this scenario, essential oils (EOs) have gained notoriety for their role in phenotype modulation, including virulence modulation. Among different EOs previously analyzed, herein we investigated the activity of Coridothymus capitatus EO (CCEO) against specific virulence factors produced by P. aeruginosa isolated from CF patients. CCEO showed inhibition of new biofilm formation and reduction in mature biofilm in about half of the tested strains. On selected strains, SEM analysis provided interesting information regarding CCEO action in a pre-adhesion assay. CCEO treatment showed a dramatic modification of the extracellular matrix (ECM) structure. Our results clearly showed a drastic reduction in pyocyanin production (between 84% and 100%) for all tested strains in the presence of CCEO. Finally, CCEO was also able to strongly affect P. aeruginosa swarming and swimming motility for almost all tested strains. In consideration of the novel results obtained on clinical strains isolated from CF patients, CCEO may be a potential candidate to limit P. aeruginosa virulence.

Inhibition of Quorum Sensing and Biofilm Formation of Esculetin on Aeromonas Hydrophila

Quorum sensing (QS) and biofilm formation inhibition activity of esculetin on Aeromonas hydrophila SHAe 115 were evaluated. Exposure to esculetin at 25, 50, and 100μg/ml significantly inhibited the production of protease and hemolysin, the formation of biofilms and attenuated the swarming motility of A. hydrophila SHAe 115. Biofilm forming inhibition was also observed through confocal laser scanning microscopy and scanning electron microscope. Quantitative real-time PCR analysis indicated that genes positively related to QS and biofilm formation were downregulated to varying degrees, while gene (litR) negatively related to biofilm formation was significantly upregulated. The phenotypic results were in good agreement with gene expression levels. These results indicated that esculetin would be a potential QS inhibitor for A. hydrophila.

Anti-Virulence Activity of the Cell-Free Supernatant of the Antarctic Bacterium Psychrobacter sp. TAE2020 against Pseudomonas aeruginosa Clinical Isolates from Cystic Fibrosis Patients

Pseudomonas aeruginosa is an opportunistic pathogen often involved in airway infections of cystic fibrosis (CF) patients. Its pathogenicity is related to several virulence factors, such as biofilm formation, motility and production of toxins and proteases. The expression of these virulence factors is controlled by quorum sensing (QS). Thus, QS inhibition is considered a novel strategy for the development of antipathogenic compounds acting on specific bacterial virulence programs without affecting bacterial vitality. In this context, cold-adapted marine bacteria living in polar regions represent an untapped reservoir of biodiversity endowed with an interesting chemical repertoire. In this paper, we investigated the biological activity of a supernatant derived from a novel Antarctic bacterium (SN_TAE2020) against specific virulence factors produced by P. aeruginosa strains isolated from FC patients. Our results clearly show a reduction in pyocyanin and protease production in the presence of SN_TAE2020. Finally, SN_TAE2020 was also able to strongly affect swarming and swimming motility for almost all tested strains. Furthermore, the effect of SN_TAE2020 was investigated on biofilm growth and texture, captured by SEM analysis. In consideration of the novel results obtained on clinical strains, polar bacteria might represent potential candidates for the discovery of new compounds limiting P. aeruginosa virulence in CF patients.

Inhibition of biofilm and quorum sensing-regulated virulence factors in Pseudomonas aeruginosa by Cuphea carthagenensis (Jacq.) J. F. Macbr. Leaf extract: An in vitro study

ETHNOPHARMCOLOGICAL RELEVANCE

Microbial biofilm formation, a quorum sensing (QS) regulated process, is one of the major causes of nosocomial and chronic infections, foodborne diseases, and associated deaths. Various approaches have been used to eradicate the menace of biofilm. Ethnomedicinal plants as potent antibiofilm agents are gaining a lot of interest in an era where the drug resistance is increasing and the availability of potent antibiotics is no longer promised. In this context, the methanol extract of Cuphea carthagenensis (CCMD), an ethno-medicinal and culinary herb, was evaluated as an antibiofilm and anti-QS agent against Pseudomonas aeruginosa.

AIM OF THE STUDY

The aim of the study is to evaluate the antibiofilm and anti-QS activity of an ethnomedicinal plant against a strong biofilm forming microorganism, P. aeruginosa.

METHODS

Antibiofilm activity of CCMD was demonstrated at different concentrations by Tissue Culture Plate, Test Tube method and other microscopic techniques. The effect of CCMD on QS and QS-related virulence factors viz. Pyocyanin, exopolymeric substance matrix (EPS), total protease, elastase, pyoverdin and swimming motility in P. aeruginosa were also evaluated. Antioxidant activity (DPPH & FRAP), total phenolic and flavonoid content were also checked. In order to determine the composition of the extract HPLC analysis was also performed.

RESULTS

In vitro study demonstrated a significant inhibition of biofilm formation (81.88 ± 2.57%) as well as production of QS-dependent virulence factors in P. aeruginosa. The extract also inhibited violacein production (83.31 ± 2.77%) in Chromobacterium violaceum which correlates with the reduction in QS-mediated virulence factors. The extract showed 64.79% ± 0.83% DPPH scavenging activity and reduction of ferricyanide complex (Fe³⁺) to the ferrous form (Fe²⁺) in DPPH and FRAP assay, respectively. Furthermore, the extract showed thermal stability and does not have any growth inhibitory effect on P. aeruginosa. The HPLC analysis demonstrated the presence of ellagic acid, ascorbic acid and hippuric acid in the extract.

CONCLUSION

This work is the first to demonstrate that C. carthagenensis can attenuate biofilm formation and QS-mediated virulence factors of P. aeruginosa. Further investigation is required to use this ethnomedicinal plant (CCMD) as an important source of antibiofilm agents.

Inhibitory effect of norharmane on Serratia marcescens NJ01 quorum sensing-mediated virulence factors and biofilm formation

Serratia marcescens NJ01, a Gram-negative bacterium, can infect tomato leaves and cause chlorosis and wilting. The present study evaluated the quorum sensing (QS) and biofilm inhibitory effects of seven carboline compounds against S. marcescens NJ01 at 20 μg ml^-1, and subsequently focused the study on norharmane as this had the best inhibitory activity. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis confirmed the down-regulation of QS and biofilm related genes bsmA, bsmB, fimA, fimC, flhD, pigA, pigC and shlA on exposure to norharmane. Fourier-Transform Infrared Spectroscopy (FT-IR) analysis showed a reduction in the major components of the exopolysaccharide (EPS) matrix such as nucleic acids, proteins and fatty acids, which are involved in forming the tertiary structure of biofilms. Norharmane exposure also enhanced the susceptibility of the biofilm to ofloxacin. Hence, norharmane has the potential for use as an antibiotic adjuvant to enhance the efficacy of conventional antibiotics to reduce pathogenic bacterial infections.

1-(4-Amino-2-hydroxyphenyl)ethanone from Phomopsis liquidambari showed quorum sensing inhibitory activity against Pseudomonas aeruginosa

Phomopsis liquidambari S47 is an endophytic fungus isolated from the leaves of Punica granatum. Here, we are the first to report a quorum sensing (QS) inhibitor 1-(4-amino-2-hydroxyphenyl)ethanone (AHE) isolated and identified from the metabolites of P. liquidambari S47. Exposure to AHE at sub-MIC concentrations notably suppressed the secretion of acyl-homoserine lactones and virulence factors in Pseudomonas aeruginosa PAO1. To investigate the metabolic variations of P. aeruginosa PAO1 exposed to AHE, magnetic resonance imaging-based metabolomic analysis was performed. AHE treatment created a disturbance in the QS system by suppressing the expressions of QS-related genes. The disturbed QS system resulted in the inhibited activity of antioxidant enzymes and thus enhanced oxidative stress. The vegetable infection assay showed that the virulence of P. aeroginosa PAO1 was attenuated which could be due to the impacts to the amino acid and nucleotide metabolism by enhanced oxidative stress. These findings suggest that AHE has a potential to become an antivirulence "agent" to tackle P. aeruginosa infection. KEY POINTS: • AHE treatment inhibited AHL secretion and virulence factors production. • AHE treatment aggravated oxidative stress and disturbed metabolism. • AHE suppressed QS-related gene expressions and reduced virulence of P. aeruginosa.

Differential Expression of Fungal Genes Determines the Lifestyle of Plectosphaerella Strains During Arabidopsis thaliana Colonization

The fungal genus Plectosphaerella comprises species and strains with different lifestyles on plants, such as P. cucumerina, which has served as model for the characterization of Arabidopsis thaliana basal and nonhost resistance to necrotrophic fungi. We have sequenced, annotated, and compared the genomes and transcriptomes of three Plectosphaerella strains with different lifestyles on A. thaliana, namely, PcBMM, a natural pathogen of wild-type plants (Col-0), Pc2127, a nonpathogenic strain on Col-0 but pathogenic on the immunocompromised cyp79B2 cyp79B3 mutant, and P0831, which was isolated from a natural population of A. thaliana and is shown here to be nonpathogenic and to grow epiphytically on Col-0 and cyp79B2 cyp79B3 plants. The genomes of these Plectosphaerella strains are very similar and do not differ in the number of genes with pathogenesis-related functions, with the exception of secreted carbohydrate-active enzymes (CAZymes), which are up to five times more abundant in the pathogenic strain PcBMM. Analysis of the fungal transcriptomes in inoculated Col-0 and cyp79B2 cyp79B3 plants at initial colonization stages confirm the key role of secreted CAZymes in the necrotrophic interaction, since PcBMM expresses more genes encoding secreted CAZymes than Pc2127 and P0831. We also show that P0831 epiphytic growth on A. thaliana involves the transcription of specific repertoires of fungal genes, which might be necessary for epiphytic growth adaptation. Overall, these results suggest that in-planta expression of specific sets of fungal genes at early stages of colonization determine the diverse lifestyles and pathogenicity of Plectosphaerella strains.

Diversity of Bacteria and Bacterial Products as Antibiofilm and Antiquorum Sensing Drugs Against Pathogenic Bacteria

The increase in antibiotic resistance of pathogenic bacteria has led to the development of new therapeutic approaches to inhibit biofilm formation as well as interfere quorum sensing (QS) signaling systems. The QS system is a phenomenon in which pathogenic bacteria produce signaling molecules that are involved in cell to cell communication, production of virulence factors, biofilm maturation, and several other functions. In the natural environment, several non-pathogenic bacteria are present as mixed population along with pathogenic bacteria and they control the behavior of microbial community by producing secondary metabolites. Similarly, non-pathogenic bacteria also take advantages of the QS signaling molecule as a sole carbon source for their growth through catabolism with enzymes. Several enzymes are produced by bacteria which disrupt the biofilm architecture by degrading the composition of extracellular polymeric substances (EPS) such as exopolysaccharide, extracellular- DNA and protein. Thus, the interference of QS system by bacterial metabolic products and enzymatic catalysis, modification of the QS signaling molecules as well as enzymatic disruption of biofilm architecture have been considered as the alternative therapeutic approaches. This review article elaborates on the diversity of different bacterial species with respect to their metabolic products as well as enzymes and their molecular modes of action. The bacterial enzymes and metabolic products will open new and promising perspectives for the development of strategies against the pathogenic bacterial infections.

Transcriptional profiling of Pseudomonas aeruginosa PAO1 in response to anti-biofilm and anti-infection agent exopolysaccharide EPS273

AIMS

Relatively, few anti-biofilm polysaccharides against Pseudomonas aeruginosa were done to investigate the underlying molecular mechanism. Exopolysaccharide EPS273 can clearly reduce biofilm formation and infection of P. aeruginosa. This study aims to investigate its anti-biofilm and anti-infection mechanism on transcriptional level.

METHODS AND RESULTS

Herein, we used an RNA-Seq transcriptomic approach to investigate the underlying anti-biofilm and anti-infection mechanism of EPS273. The expression levels of a large number of genes were changed after P. aeruginosa PAO1 was treated with EPS273. Especially, the genes related to biofilm formation, such as gene involved in production of extracellular matrix and virulence factor, genes involved in flagella and cell motility and genes involved in iron acquisition. Notably, the expression levels of genes involved in regulatory and signal transduction were markedly downregulated, such as two-component system PhoP-PhoQ and quorum sensing (QS) system LasI/LasR and RhlI/RhlR. Furthermore, when genes phoP and phoQ were disrupted, respectively, the reduction of biofilm formation and cell motility in mutant △phoP or △phoQ was also detected.

CONCLUSION

EPS273 may exert its anti-biofilm and anti-infection function by downregulating gene expression of two-component system PhoP-PhoQ and QS systems LasI/LasR and RhlI/RhlR of P. aeruginosa, which further regulated expression of genes involved in biofilm formation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our data will expand understanding of anti-biofilm mechanisms of polysaccharides on transcriptomic level.

Hypertonic glucose inhibits growth and attenuates virulence factors of multidrug-resistant Pseudomonas aeruginosa

BACKGROUND

Pseudomonas aeruginosa is the most common Gram-negative pathogen responsible for chronic wound infections, such as diabetic foot infections, and further exacerbates the treatment options and cost of such conditions. Hypertonic glucose, a commonly used prolotherapy solution, can accelerate the proliferation of granulation tissue and improve microcirculation in wounds. However, the action of hypertonic glucose on bacterial pathogens that infect wounds is unclear. In this study, we investigated the inhibitory effects of hypertonic glucose on multidrug-resistant P. aeruginosa strains isolated from diabetic foot infections. Hypertonic glucose represents a novel approach to control chronic wound infections caused by P. aeruginosa.

RESULTS

Four multidrug-resistant P. aeruginosa clinical strains isolated from diabetic foot ulcers from a tertiary hospital in China and the reference P. aeruginosa PAO1 strain were studied. Hypertonic glucose significantly inhibited the growth, biofilm formation, and swimming motility of P. aeruginosa clinical strains and PAO1. Furthermore, hypertonic glucose significantly reduced the production of pyocyanin and elastase virulence factors in P. aeruginosa. The expression of major quorum sensing genes (lasI, lasR, rhlI, and rhlR) in P. aeruginosa were all downregulated in response to hypertonic glucose treatment. In a Galleria mellonella larvae infection model, the administration of hypertonic glucose was shown to increase the survival rates of larvae infected by P. aeruginosa strains (3/5).

CONCLUSIONS

Hypertonic glucose inhibited the growth, biofilm formation, and swimming motility of P. aeruginosa, as well as reduced the production of virulence factors and quorum sensing gene expression. Further studies that investigate hypertonic glucose therapy should be considered in treating chronic wound infections.

Inhibition of quorum sensing-associated virulence factors and biofilm formation in Pseudomonas aeruginosa PAO1 by Mycoleptodiscus indicus PUTY1

Pseudomonas aeruginosa is the second most emerging multidrug-resistant, opportunistic pathogen after Acinetobacter baumannii that poses a threat in nursing homes, hospitals, and patients who need devices such as ventilators and blood catheters. Its ability to form quorum sensing-regulated virulence factors and biofilm makes it more resistant to top most therapeutic agents such as carbapenems and next-generation antibiotics. In the current study, we studied the quorum quenching potential of secondary metabolites of Mycoleptodiscus indicus PUTY1 strain. In vitro observation showed a mitigation in virulence factors such as rhamnolipids, protease, elastase pyocyanin, exopolysaccharides, and hydrogen cyanide gas. Furthermore, a significant reduction in the motility such as swimming, swarming, twitching, and inhibition in biofilm formation by Pseudomonas aeruginosa PAO1 was observed. Results of in vitro studies were further confirmed by in silico studies through docking and molecular dynamic simulation of GC-MS-detected compounds of Mycoleptodiscus indicus employing LasR and RhlR proteins. Both in vitro and in silico observations indicate a new alternative approach for combating virulence of Pseudomonas aeruginosa by targeting its protein receptors LasR and RhlR. Graphical abstract.

Anti-virulence potential of basil and sage essential oils: Inhibition of biofilm formation, motility and pyocyanin production of Pseudomonas aeruginosa isolates

The effects of basil (Ocimum basilicum) and sage (Salvia officinalis) essential oils on selected virulence factors (biofilm formation, mature biofilm resistance, motility, and pyocyanin production) of Pseudomonas aeruginosa clinical isolates were evaluated in the present study for the first time. The two essential oils were chemically characterized by GC and GC-MS analyses. Linalool and (E)-anethole were found to be the main components of the investigated basil oil, while α-thujone and camphor were the major constituents of the studied sage essential oil. The oils inhibited biofilm formation up to 99.9% vs control, and significant reductions (74.7-99.9%) were also noted when the oils were applied to mature biofilms. Likewise, swimming, swarming, and twitching motility patterns were highly affected by both oils. The basil and sage oils reduced pyocyanin production by 13.32-55.6% and 5.0-58.7%, respectively. Thus, basil and sage essential oils are potentially highly efficient antipseudomonal agents that could be used against both acute and chronic infections.

Growth inhibition and metabolomic analysis of Xanthomonas oryzae pv. oryzae treated with resveratrol

Background

Xanthomonas oryzae pv. oryzae (Xoo) can cause destructive bacterial blight in rice. As an antibacterial, resveratrol may inhibit Xoo growth. This study focused on the potential structural-activity relationship of resveratrol and its derivatives against Xoo growth, and ¹H-NMR-based metabolomic analysis was applied to investigate the global metabolite changes in Xoo after resveratrol treatment.

Results

Resveratrol showed the strongest inhibitory effects on Xoo growth compared with its derivatives, which lacked double bonds (compounds 4–6) or hydroxyls were substituted with methoxyls (compounds 7–9). The IC₅₀ of resveratrol against Xoo growth was 11.67 ± 0.58 μg/mL. Results indicated that the double bond of resveratrol contributed to its inhibitory effects on Xoo growth, and hydroxyls were vital for this inhibition. Interestingly, resveratrol also significantly inhibited Xoo flagellum growth. Based on ¹H-NMR global metabolic analysis, a total of 30 Xoo metabolites were identified, the changes in the metabolic profile indicated that resveratrol could cause oxidative stress as well as disturb energy, purine, amino acid, and NAD⁺ metabolism in Xoo, resulting in the observed inhibitory effects on growth.

Conclusions

This study showed that the double bond of resveratrol contributed to its inhibitory effects on Xoo growth, and hydroxyls were also the important active groups. Resveratrol could cause oxidative stress of Xoo cells, and disturb the metabolism of energy, purine, amino acid and NAD +, thus inhibit Xoo growth.

Quorum sensing inhibition and tobramycin acceleration in Chromobacterium violaceum by two natural cinnamic acid derivatives

Chromobacterium violaceum, one free-living Gram-negative bacterium, is abundantly presented in tropics and sub-tropics soil and aquatic environment; it is also an opportunistic human pathogen. Here, two cinnamic acid derivatives, i.e., 4-dimethylaminocinnamic acid (DCA) and 4-methoxycinnamic acid (MCA), were identified as potential quorum sensing (QS) and biofilm inhibitors in C. violaceum ATCC12472. Both DCA (100 μg/mL) and MCA (200 μg/mL) inhibited the levels of N-decanoyl-homoserine lactone (C10-HSL) and reduced the production of certain virulence factors in C. violaceum, including violacein, hemolysin, and chitinase. Metabolomics analysis indicated that QS-related metabolites, such as ethanolamine and L-methionine, were down-regulated after treatment with DCA and MCA. Quantitative real-time polymerase chain reaction (qRT-PCR) demonstrated that DCA and MCA markedly suppressed the expression of two QS-related genes (cviI and cviR). In addition, DCA and MCA also inhibited biofilm formation and enhanced the susceptibility of biofilms to tobramycin, which was evidenced by scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). Our results indicated that DCA and MCA can serve as QS-based agent for controlling pathogens.Key Points • DCA and MCA inhibited QS and biofilm formation in C. violaceum.• The combination of DCA or MCA and tobramycin removed the preformed biofilm of C. violaceum. • DCA or MCA inhibited virulence factors and expressions of cviI and cviR of C. violaceum.• DCA or MCA are potential antibiotic accelerants for treating C. violaceum infection.

Effects of Lysozyme, Proteinase K, and Cephalosporins on Biofilm Formation by Clinical Isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen that can form biofilms, which confer resistance to immune clearance and antibacterial treatment. Therefore, effective strategies to prevent biofilm formation are warranted. Here, 103 P. aeruginosa clinical isolates were quantitatively screened for biofilm formation ability via the tissue culture plate method. The effects of lysozyme (hydrolytic enzyme) and proteinase K (protease) on biofilm formation were evaluated at different concentrations. Lysozyme (30 μg/mL), but not proteinase K, significantly inhibited biofilm formation (19% inhibition). Treatment of 24-hour-old biofilms of P. aeruginosa isolates with 50 times the minimum inhibitory concentrations (MICs) of ceftazidime and cefepime significantly decreased the biofilm mass by 32.8% and 44%, respectively. Moreover, the exposure of 24-hour-old biofilms of P. aeruginosa isolates to lysozyme (30 μg/mL) and 50 times MICs of ceftazidime or cefepime resulted in a significant reduction in biofilm mass as compared with the exposure to lysozyme or either antibacterial agent alone. The best antibiofilm effect (49.3%) was observed with the combination of lysozyme (30 μg/mL) and 50 times MIC of cefepime. The promising antibiofilm activity observed after treatment with 50 times MIC of ceftazidime or cefepime alone or in combination with lysozyme (30 μg/mL) is indicative of a novel strategy to eradicate pseudomonal biofilms in intravascular devices and contact lenses.

Phomopsis tersa as Inhibitor of Quorum Sensing System and Biofilm Forming Ability of Pseudomonas aeruginosa

Endophytic fungi provide rich reservoir for novel antimicrobial compounds. An endophytic fungus, from Carica papaya plant identified as Phomopsis tersa, was investigated for attenuating the quorum sensing mediated pathogenicity of Pseudomonas aeruginosa PAO1. Crude extract of P. tersa was found to reduce the production of redox-active pigments-pyocyanin and pyoverdine in P. aeruginosa PAO1 by 92.46% and 71.55%, respectively at sub-MIC concentration of 900 μg/mL. In addition, the crude extract was also able to inhibit the expression of virulence factors involved in biofilm formation: exopolysaccharide (72.21%) and alginate (72.50%). Secretion of cell-lytic enzymes was also found to be reduced: chitinase by 79.73% and elastase by 74.30%. 3-Isobutylhexahydropyrrolo[1,2-a]pyrazine-1,4-dione identified from GC-MS analysis, displayed favorable molecular interactions with P. aeruginosa transcriptional regulators, LasR and RhlR with good docking scores of - 6.873 kJ/mol and - 6.257 kJ/mol, respectively. The study thus reveals the potential use of P. tersa for discovering drugs against infectious pathogens.