Tannin-rich fraction from Terminalia catappa inhibits quorum sensing (QS) in Chromobacterium violaceum and the QS-controlled biofilm maturation and LasA staphylolytic activity in Pseudomonas aeruginosa

Inhibitory effect of natural compounds on quorum sensing system in Pseudomonas aeruginosa: a helpful promise for managing biofilm community

Pseudomonas aeruginosa biofilm is a community of bacteria that adhere to live or non-living surfaces and are encapsulated by an extracellular polymeric substance. Unlike individual planktonic cells, biofilms possess a notable inherent resistance to sanitizers and antibiotics. Overcoming this resistance is a substantial barrier in the medical and food industries. Hence, while antibiotics are ineffective in eradicating P. aeruginosa biofilm, scientists have explored alternate strategies, including the utilization of natural compounds as a novel treatment option. To this end, curcumin, carvacrol, thymol, eugenol, cinnamaldehyde, coumarin, catechin, terpinene-4-ol, linalool, pinene, linoleic acid, saponin, and geraniol are the major natural compounds extensively utilized for the management of the P. aeruginosa biofilm community. Noteworthy, the exact interaction of natural compounds and the biofilm of this bacterium is not elucidated yet; however, the interference with the quorum sensing system and the inhibition of autoinducer production in P. aeruginosa are the main possible mechanisms. Noteworthy, the use of different drug platforms can overcome some drawbacks of natural compounds, such as insolubility in water, limited oral bioavailability, fast metabolism, and degradation. Additionally, drug platforms can deliver different antibiofilm agents simultaneously, which enhances the antibiofilm potential of natural compounds. This article explores many facets of utilizing natural compounds to inhibit and eradicate P. aeruginosa biofilms. It also examines the techniques and protocols employed to enhance the effectiveness of these compounds.

Polyphenols and CRISPR as Quorum Quenching Agents in Antibiotic-Resistant Foodborne Human Pathogens (Salmonella Typhimurium, Campylobacter jejuni and Escherichia coli 0157:H7)

Antibiotic resistance in foodborne pathogens is an increasing threat to global human health. Among the most prevalent antibiotic-resistant bacteria are Salmonella enterica serovar Typhimurium, Campylobacter jejuni and E. coli 0157:H7. Control of these and other pathogens requires innovative approaches, i.e., discovering new molecules that will inactivate them, or render them less virulent without inducing resistance. Recently, several polyphenol molecules have been shown to possess such characteristics. Also, the use of CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) approaches has recently been proposed for such purpose. This review summarizes the main findings regarding the application of both approaches to control the above-mentioned foodborne pathogens by relying on Quorum Sensing interference (Quorum Quenching) mechanisms and highlights the avenues needed for further research.

Polyphenols and CRISPR as Quorum Quenching Agents in Antibiotic-Resistant Foodborne Human Pathogens (Salmonella Typhimurium, Campylobacter jejuni and Escherichia coli 0157:H7)

Antibiotic resistance in foodborne pathogens is an increasing threat to global human health. Among the most prevalent antibiotic-resistant bacteria are Salmonella enterica serovar Typhimurium, Campylobacter jejuni and E. coli 0157:H7. Control of these and other pathogens requires innovative approaches, i.e., discovering new molecules that will inactivate them, or render them less virulent without inducing resistance. Recently, several polyphenol molecules have been shown to possess such characteristics. Also, the use of CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) approaches has recently been proposed for such purpose. This review summarizes the main findings regarding the application of both approaches to control the above-mentioned foodborne pathogens by relying on Quorum Sensing interference (Quorum Quenching) mechanisms and highlights the avenues needed for further research.

Anti-quorum Sensing of Terminalia catappa and Murraya koenigii Against Streptococcus mutans

Introduction Dental biofilm constitutes micro-organisms existing in an intercellular matrix containing organic and inorganic materials derived from saliva, gingival crevicular fluid, and bacterial products. Dental plaque biofilm inhibition by certain herbs and medicinal plants has been used as a treatment modality for the prevention of white spot lesions in orthodontic subjects. The aim of this study was to evaluate the anti-quorum sensing and anti-biofilm activity of Terminalia catappa and Murraya koenigiiagainst Streptococcus mutans. Materials and methods Samples of dental plaque were taken from patients receiving orthodontic care. The colonies of the S. mutans were isolated and biochemical characterization was done. Leaf extracts of Terminalia catappa and Murraya koenigii were used in the study. Methanolic extracts were subjected to evaluation of minimum inhibitory concentration (MIC) using the broth microdilution (two-fold) method and anti-biofilm activity using the crystal violet staining method. Results  The MIC of methanol leaf extracts of Murraya koenigii against S. mutans was noted at 0.62 mg/ml and Terminalia catappa at 1.25 mg/ml. At the lowest concentration of 0.03 mg and 0.01 mg methanol extract of Murraya koenigii had remarkably inhibited biofilm formation of 57.6% and 43.6% against S. mutans, respectively. Terminalia catappa leaf extracts did not show any anti-biofilm activity when the organisms were grown in the presence of S. mutans. Conclusion  Both Murraya koenigii and Terminalia catappa had antibacterial effects against S. mutans and Murray koenigii remarkably inhibited biofilm formation by S. mutans.

Antibacterial and anti-inflammatory activity of plant species used in traditional poultry ethnomedicine in Zimbabwe: A first step to developing alternatives to antibiotic poultry feed additives

ETHNOPHARMACOLOGICAL RELEVANCE

Global interest in phytogenic feed additives as alternatives to antibiotics in feed has been spurred by the banning of antibiotic growth promoters by several countries. Suitable plant extracts for development of phytogenic feed additives should have therapeutic value and should also be safe.

AIM OF STUDY

The aim of this study was to evaluate the antibacterial, antioxidant and anti-lipoxygenase activities as well as cytotoxicity of selected plant species used in poultry ethnomedicine in Zimbabwe.

METHODS

Antibacterial activity was determined against three ATCC strains (Staphylococcus aureus, Escherichia coli, Salmonella Enteritidis) and two clinical strains isolated from chickens (Escherichia coli and Salmonella Gallinarum) using a two-fold serial microdilution assay. Qualitative antibacterial bioautography was also carried out using the ATCC strains. Antioxidant activities of crude acetone and methanol extracts were determined using free radical scavenging assays whilst anti-lipoxygenase activity was evaluated using a ferrous oxidation-xylenol orange (FOX) assay. Cytotoxicity was evaluated using a tetrazolium-based colorimetric assay (MTT assay) on Vero monkey kidney cells.

RESULTS

Erythrina abyssinica had the best antibacterial activity against both ATCC strains and clinical strains with minimum inhibitory concentration (MIC) values ranging from 0.02 to 0.156 mg/ml. Aloe greatheadii, Adenia gummifera (leaves), Senna singueana and Aloe chabaudii had moderate activity against the poultry pathogens. Bioautography showed that all ten plant species have antibacterial activity against the tested microorganisms with E. abyssinica and S. singueana having prominent bands of inhibition against both Gram-negative and Gram-positive bacteria. The acetone extract of S. singueana and the methanol extract of Euphorbia matabelensis had the most powerful antioxidant activities with mean IC₅₀ values of 1.43 μg/ml and 1.31 μg/ml respectively in the ABTS assay which were comparable with those of the positive controls (ascorbic acid and trolox). Bobgunnia madagascariensis, A. chabaudii, E. abyssinica and Tridactyle bicaudata extracts had reasonable antioxidant activity. The S. singueana extract had the most potent anti-lipoxygenase activity with a mean IC₅₀ value of 1.72 μg/ml. The cytotoxicity results showed that only the acetone extracts of A. greatheadii and S. singueana were relatively safe at concentrations that were active against the tested microorganisms (selective index >1). Regarding anti-lipoxygenase activity, extracts of B. madagascariensis, S. singueana, T. bicaudata and E. matabelensis were more active than toxic (selective index >5) indicating anti-inflammatory potential.

CONCLUSIONS

This study showed that S. singueana had a cocktail of therapeutic activity and supports further investigation of this plant species for development of phytogenic poultry feed additives. Other plant species with noteworthy biological activities include B. madagascariensis, E. abyssinica, A. greatheadii, T. bicaudata and E. matabelensis.

Effect of chemical modifications of tannins on their antimicrobial and antibiofilm effect against Gram-negative and Gram-positive bacteria

Background

Tannins have demonstrated antibacterial and antibiofilm activity, but there are still unknown aspects on how the chemical properties of tannins affect their biological properties. We are interested in understanding how to modulate the antibiofilm activity of tannins and in delineating the relationship between chemical determinants and antibiofilm activity.

Materials and methods

The effect of five different naturally acquired tannins and their chemical derivatives on biofilm formation and planktonic growth of Salmonella Typhimurium, Pseudomonas aeruginosa, Escherichia coli and Staphylococcus aureus was determined in the Calgary biofilm device.

Results

Most of the unmodified tannins exhibited specific antibiofilm activity against the assayed bacteria. The chemical modifications were found to alter the antibiofilm activity level and spectrum of the tannins. A positive charge introduced by derivatization with higher amounts of ammonium groups shifted the anti-biofilm spectrum toward Gram-negative bacteria, and derivatization with lower amounts of ammonium groups and acidifying derivatization shifted the spectrum toward Gram-positive bacteria. Furthermore, the quantity of phenolic OH-groups per molecule was found to have a weak impact on the anti-biofilm activity of the tannins.

Conclusion

We were able to modulate the antibiofilm activity of several tannins by specific chemical modifications, providing a first approach for fine tuning of their activity and antibacterial spectrum.

The Anti-Biofilm Activity and Mechanism of Apigenin-7-O-Glucoside Against Staphylococcus aureus and Escherichia coli

Introduction

This study aimed to examine the anti-biofilm activity and mechanism of gallic acid (GA), kaempferol-7-O-glucoside (K7G) and apigenin-7-O-glucoside (A7G) against Staphylococcus aureus and Escherichia coli.

Methods

The antibacterial activity of the natural compounds was determined by serial dilution method. The inhibitory activity of natural compounds on biofilms was determined by crystal violet staining method. The effects and mechanisms of natural compounds on bacterial biofilms were analyzed by atomic force microscopy.

Results

In our study, compared with GA and K7G, A7G was found to exhibit the strongest anti-biofilm and antibacterial activities. The minimum biofilm inhibitory concentration (MBIC) of A7G against S. aureus and E. coli was 0.20 mg/mL and 0.10 mg/mL, respectively. The inhibition rates of 1/2 MIC of A7G on biofilms of S. aureus and E. coli were 88.9%, and 83.2% respectively. Moreover, atomic force microscope (AFM) images showed the three-dimensional biofilm morphology of S. aureus and E. coli, and the results indicated that A7G was highly effective in biofilm inhibition.

Discussion

It was found that the inhibition of A7G on biofilm was achieved through inhibiting on exopolysaccharides (EPS), quorum sensing (QS), and cell surface hydrophobicity (CSH). A7G exerted strong anti-biofilm activities by inhibiting EPS production, QS, and CSH. Hence, A7G, as a natural substance, could be a promising novel antibacterial and anti-biofilm agent for control of biofilm in food industry.

Anti-quorum sensing evaluation of methyleugenol, the principal bioactive component, from the Melaleuca bracteata leaf oil

Quorum sensing (QS) is a cell-to-cell communication in bacteria that couples gene expression through the accumulation of signaling molecules, which finally induce the production of several virulence factors and modulate bacterial behaviors. Plants have evolved an array of quorum sensing inhibitors (QSIs) to inhibit the pathogens, of which aromatic compounds are widely recognized. The essential oil of Melaleuca bracteata was found to exhibit anti-quorum sensing activity, and its principal bioactive component, methyleugenol (ME), had been isolated in our previous study. Here, ME interfered effectively with the QS-regulated processes of toxin secretion in Chomobacterium violaceum ATCC31532, resulting in strong inhibition of QS genes, cviR, cviI, vioA-E, hmsHNR, lasA-B, pilE1-3, and hcnABC, leading to impaired virulence, including violacein production, biofilm biomass, and swarming motility. The accumulation of the signal molecule (N-hexanoyl-DL-homoserine lactone, C6-HSL) in C. violaceum declined upon treatment with ME, suggesting an inhibition effect on the C6-HSL production, and the ME was also capable of degrading the C6-HSL in vitro assay. Molecular docking technique and the consumption change of exogenous C6-HSL in C. violaceum CV026 revealed the anti-QS mechanism of ME consisted of inhibition of C6-HSL production, potentially via interaction with CviR and/or CviI protein. Collectively, the isolated ME, the principal active components of M. bracteata EO, exhibited a wide range of inhibition processes targeting C. violaceum QS system, which supports the potential anti-pathogenic use of M. bracteata EO and ME for treatment of pathogen contamination caused by bacterial pathogens.

Terminalia catappa aqueous leaf extract reverses insulin resistance, improves glucose transport and activates PI3K/AKT signalling in high fat/streptozotocin-induced diabetic rats

Rising prevalence of type 2 diabetes mellitus (T2DM) in sub-Saharan Africa has necessitated surveys of antidiabetic medicinal plants. This study assessed the antidiabetic mechanism of Terminalia catappa aqueous leaf extract (TCA) in high fat/low dose streptozotocin-induced type 2 diabetic rats. T2DM was induced by a combination of high-fat diet and low dose STZ (30 mg/kg bw) and the animals were administered with TCA (400 and 800 mg/kg bw) orally daily for 28 days. Biochemical parameters and indices for diabetes including renal function tests and pancreatic histology were evaluated. Relative expression of hepatic insulin resistance, signalling and glucose transport genes were also assessed. Induction of T2DM resulted in significant (p < 0.05) weight loss, dysregulated glucose level and clearance, electrolyte imbalance and disrupted diabetic biochemical parameters. Diabetes onset also perturbed β-cell function and insulin resistance indices, damaged pancreas microanatomy, while disrupting the expression of insulin receptor substrate 1 (IRS-1), phosphatidylinositol 3-kinase (PI3K), protein kinase B (AKT) and glucose transporter isoform 4 (GLUT-4) mRNA. Oral treatment of diabetic animals with TCA significantly (p < 0.05) ameliorated alterations due to T2DM induction in a manner comparable with glibenclamide. These results suggest TCA exerts its antidiabetic action by reversing insulin resistance, improving glucose transport and activating PI3K/AKT signalling.

Cardio-protective effects of Terminalia catappa leaves and Terminalia chebula fruit extract in doxorubicin-induced cardiomyopathy in rats

INTRODUCTION

The cardio-protective effects of Terminalia catappa and Terminalia chebula are well-recognized in Ayurveda for its antimicrobial, antidiabetic and antioxidant potentials. The present study evaluates the effects of T. catappa leaves (Tct.LE) and T. chebula fruits (Tce.FE) against doxorubicin (DOX)-induced rats through analysis of the cardiac biomarkers, tricarboxylic acid (TCA) cycle enzymes and respiratory chain enzymes for their cardio-protective properties. Materials and methods: This study includes 42 adult male Albino Wistar rats randomized into seven groups for 21-days. Groups were categorized as control; DOX (1.5 mg/kg) induced negative control; basal diet with 300 mg/kg of Tct.LE, with 300 mg/kg Tce.FE; DOX with 300 mg/kg of Tct.LE, Tce.FE, and propranolol (25mg/kg). Results and Discussion: The doses of 300 mg/kg of both plants have a significant effect on the TCA cycle, respiratory and lysosomal enzymes activity. The troponin levels are significantly reduced in plant treated group than the DOX-treated rats when compared with the control and propranolol treated group. Likewise, the increased level of creatine kinase-muscle/MB, creatine kinase and lipid profile in the DOX-treated animals were significantly reduced upon being treated with extracts. Conclusion: The cardio-protective activity of Tct.LE leaves and Tce.FE indicate its potential use in the management of cardiovascular diseases.

CLINICAL SIGNIFICANCE

The prevalence of cardiovascular disease is increasing day-by-day in this industrial world with leading cause of mortality and morbidity. Many researches are presently concentrated on the plant-based medicine due to its safety and free from side effects. Hence, the present study aims to document the potential cardio-protective benefits of Terminalia catappa and Terminalia chebula.

Cholera outbreak: antibiofilm activity, profiling of antibiotic-resistant genes and virulence factors of toxigenic Vibrio cholerae isolates reveals concerning traits

Vibrio cholerae is a biofilm-forming pathogen with various virulence phenotypes and antimicrobial resistance traits. Phenotypic characteristics play a critical role in disease transmission and pathogenesis. The current study elucidated antibiofilm formation activity, profiled antibiotic-resistant genes and virulence factors of toxigenic Vibrio cholerae isolates from the cholera outbreak in Kisumu County, Kenya. Vibrio cholerae O1 isolates collected during the 2017 cholera outbreak in Kisumu County, Kenya, were utilized. Biofilm and virulence factors were profiled using standard procedures. The study confirmed 100 isolates as Vibrio cholerae, with 81 of them possessing cholera toxin gene (ctxA). Additionally, 99 of the isolates harboured the toxR gene. The study further revealed that 81 and 94 of the isolates harboured the class I integron (encoded by inDS gene) and integrating conjugative element (ICE), respectively. Antibiotic resistance assays confirmed tetracycline resistance genes as the most abundant (97 isolates). Among them were seven isolates resistant to commonly used antibiotics. The study further screened the isolates for antibiofilm formation using various antibiotics. Unlike the four strains (03/17–16, 02/17–09, 04/17–13), three of the strains (04/17–07, 06/17–14 and 05/17–03) did not form biofilms. Further, all the seven isolates that exhibited extensive antibiotic resistance produced haemolysin while 71.42%, 85.71 and 71.42 % of them produced protease, phospholipases and lipase, respectively. This study provides and in-depth understanding of essential features that were possibly responsible for V. cholerae outbreak. Understanding of these features is critical in the development of strategies to combat future outbreaks.

Design of Oleanolic Acid-based Hybrid Compounds as Potential Pharmaceutical Scaffolds

Background:

Infectious diseases, as well as cancer, are the leading causes of death worldwide. Drug resistance usually results in their treatment requiring a combination of two or more drugs.

Objective:

Oleanolic-based hybrid compounds were prepared via esterification and characterized using FTIR, NMR and LC-MS. In vitro antibacterial and in vitro cytotoxicity studies were performed.

Method:

Oleanolic acid was hybridized with selected known pharmaceutical scaffolds via the carboxylic acid functionality in order to develop therapeutics with increased biological activity. Antibacterial activity was determined using the micro-dilution assay against selected Gram-positive and Gram-negative bacteria and cytotoxicity using the sulforhodamine B assay.

Results:

Compound 8 displayed potent antibacterial effect against five strains of bacteria, such as Bacillus subtilis, Staphylococcus aureus, Proteus vulgaris, Klebsiella oxytoca, and Escherichia coli, with MIC values of 1.25, 0.078, 0.078, 1.25, 1.25 mg/mL when compared to the control, oleanolic acid (MIC = 2.5 mg/mL). Furthermore, in vitro cytotoxicity, as determined using the SRB assay, against selected cancer cells revealed that compound 7 was the most cytotoxic on MDA, DU145, and MCF-7 cell lines with IC50 values of 69.87 ± 1.04, 73.2 ± 1.08, and 85.27 ± 1.02 μg/mL, respectively, compared to oleanolic acid with an IC50 > 200 μg/mL.

Conclusion:

Hybridization of oleanolic acid was successful, and further development of these potential antibacterial compounds with reduced cytotoxicity is therefore warranted.

Pseudomonas aeruginosa Biofilm Formation and Its Control

Microbes are hardly seen as planktonic species and are most commonly found as biofilm communities in cases of chronic infections. Biofilms are regarded as a biological condition, where a large group of microorganisms gets adhered to a biotic or abiotic surface. In this context, Pseudomonas aeruginosa, a Gram-negative nosocomial pathogen is the main causative organism responsible for life-threatening and persistent infections in individuals affected with cystic fibrosis and other lung ailments. The bacteria can form a strong biofilm structure when it adheres to a surface suitable for the development of a biofilm matrix. These bacterial biofilms pose higher natural resistance to conventional antibiotic therapy due to their multiple tolerance mechanisms. This prevailing condition has led to an increasing rate of treatment failures associated with P. aeruginosa biofilm infections. A better understanding of the effect of a diverse group of antibiotics on established biofilms would be necessary to avoid inappropriate treatment strategies. Hence, the search for other alternative strategies as effective biofilm treatment options has become a growing area of research. The current review aims to give an overview of the mechanisms governing biofilm formation and the different strategies employed so far in the control of biofilm infections caused by P. aeruginosa. Moreover, this review can also help researchers to search for new antibiofilm agents to tackle the effect of biofilm infections that are currently imprudent to conventional antibiotics.

Counteraction of Biofilm Formation and Antimicrobial Potential of Terminalia catappa Functionalized Silver Nanoparticles against Candida albicans and Multidrug-Resistant Gram-Negative and Gram-Positive Bacteria

Biofilms not only protect bacteria and Candida species from antibiotics, but they also promote the emergence of drug-resistant strains, making eradication more challenging. As a result, novel antimicrobial agents to counteract biofilm formation are desperately needed. In this study, Terminalia catappa leaf extract (TCE) was used to optimize the TCE-capped silver nanoparticles (TCE-AgNPs) via a one-pot single-step method. Varied concentrations of TCE have yielded different sized AgNPs. The physico-chemical characterization of TCE-AgNPs using UV-Vis, SEM, TEM, FTIR, and Raman spectroscopy have confirmed the formation of nanostructures, their shape and size and plausible role of TCE bio-active compounds, most likely involved in the synthesis as well as stabilization of NPs, respectively. TCE-AgNPs have been tested for antibiofilm and antimicrobial activity against multidrug-resistant Pseudomonas aeruginosa (MDR-PA), methicillin-resistant Staphylococcus aureus (MRSA), and Candida albicans using various microbiological protocols. TCE-Ag-NPs-3 significantly inhibits biofilm formation of MDR-PA, MRSA, and C. albicans by 73.7, 69.56, and 63.63%, respectively, at a concentration of 7.8 µg/mL, as determined by crystal violet microtiter assay. Furthermore, SEM micrograph shows that TCE-AgNPs significantly inhibit the colonization and adherence of biofilm forming cells; individual cells with loss of cell wall and membrane integrity were also observed, suggesting that the biofilm architecture and EPS matrix were severely damaged. Moreover, TEM and SEM images showed that TCE-AgNPs brutally damaged the cell wall and membranes of MDR-PA, MRSA, and C. albicans. Additionally, extreme ultrastructural changes such as deformation, disintegration, and separation of cell wall and membrane from the cells, have also been observed, indicating significant loss of membrane and cell wall integrity, which eventually led to cell death. Overall, the research revealed a simple, environmentally friendly, and low-cost method for producing colloidal TCE-AgNPs with promising applications in advanced clinical settings against broad-spectrum biofilm-forming antibiotic-resistant bacteria and candida strains.

Antibacterial Activity and Time-kill Assay of Terminalia catappa L. and Nigella sativa L. against Selected Human Pathogenic Bacteria

The current investigation aims to test the susceptibility of human pathogenic clinical isolates and MTCC strains to leaf and seed extracts of Terminalia catappa and Nigella sativa. Disc diffusion assay, micro dilution assay and minimum Bactericidal Concentration investigated the susceptibility of bacteria to the test extracts. The active extract was subjected to phytochemical screening, separation of the phytochemicals by Thin Layer Chromatography, bioactivity guided assay and Time- kill assay. Acetone and methanol extracts of T.catappa revealed, significant inhibition of clinical origin Staphylococcus aureus followed by Proteus vulgaris and the MTCC strains Staphylococcus aureus, Salmonella typhi, Pseudomonas aeroginosa and Bacillus subtilis. Nigella sativa inhibited the growth of clinical origin Staph.aureus and MTCC strain of Staph.aureus, Salmonella typhi and B.subtilis. Minimum inhibitory concentration for all the test bacteria was reported in the range of 5000μg/ml to 9 μg/ml in T. catappa extract. Most sensitive being the clinical isolate Staph. aureus and Proteus vulgaris. The bactericidal concentration for the test bacteria was found to be between 5000μg/ml and 625μg/ml. Phyto-chemical analysis of leaf extracts of T. catappa found to have dominated by polyphenols (Terpenoids, steroids, flavonoids, flavones, saponins and tannins) and N.sativa extracts recorded the presence of alkaloids, proteins and oils and fats. TLC profiling of the acetone extract revealed many antibacterial active bands. Bands having Retention factor 0.47 and 0.52 were active against the test bacteria. Time kill assay of the acetone extract of T. catappa were carried out for the first time. The extract exhibited dose dependent bactericidal and bacteriostatic activity against the clinical isolates.

Quorum Sensing Inhibition or Quenching in Acinetobacter baumannii: The Novel Therapeutic Strategies for New Drug Development

Acinetobacter baumannii is a Gram-negative opportunistic nosocomial pathogen, which can cause ventilator-related and blood infection in critically ill patients. The resistance of A. baumannii clinical isolates to common antimicrobials and their tolerance to desiccation have emerged as a serious problem to public health. In the process of pathogenesis, bacteria release signals, which regulate virulence and pathogenicity-related genes. Such bacteria coordinate their virulent behavior in a cell density-dependent phenomenon called quorum sensing (QS). In contrast, the two main approaches of QS interference, quorum sensing inhibitors (QSIs) and quorum quenching (QQ) enzymes, have been developed to reduce the virulence of bacteria, thus reducing the pressure to produce bacterial drug resistance. Therefore, QSIs or QQ enzymes, which interfere with these processes, might potentially inhibit bacterial QS and ultimately biofilm formation. In this review, we aim to describe the state-of-art in the QS process in A. baumannii and elaborate on the use of QSIs or QQ enzymes as antimicrobial drugs in various potential sites of the QS pathway.

Synthesis, antibacterial, and cytotoxicity evaluation of oleanolic acid-4-aminoquinoline based hybrid compounds

AIM

To prepare a class of oleanolic-based compounds.

BACKGROUND

Conventional drugs used to treat infectious diseases suffer from limitations such as drug toxicity and drug resistance. The resistance of microbes to antimicrobial agents is a significant challenge in treating microbial infections. Combining two or more drugs with different modes of action to treat microbial infections results in a delay in developing drug resistance by the microbes. However, it is challenging to select the appropriate choice of drugs for combination therapy due to the differences in stability and pharmacokinetic profile of the drugs.Therefore, developing hybrid compounds using the existing drugs is a promising approach to design effective antimicrobial agents.

OBJECTIVES

To prepare oleanolic-based hybrid compounds followed by characterization, in vitro antibacterial, and cytotoxicity evaluation.

METHODS

Oleanolic acid-4-aminoquinoline-based hybrid compounds weresynthesized via esterification and amidation. The compounds werecharacterized using FTIR, NMR, and UHPLC-HRMS. Oleanolic acid was isolated from the flower buds of Syszygium aromaticum (L.) Merr. & L.M.Perry, a specie from Kingdom Plantae, order Mytales in Myrtaceae family. Their antibacterial and cytotoxicity activity was determined against selected strains of bacteria assessed using the microdilution assay and sulforhodamine B assay against selected cancer cell lines.

RESULTS

The synthesized hybrid compounds exhibited significant antibacterial activity against the Gram-positive bacteria Enterococcus faecalis (ATCC13047), Bacillus subtilis (ATCC19659), Staphylococcus aureus as well as Gram-negative bacteria,Klebsiella oxytoca (ATCC8724), Escherischia coli (ATCC25922), and Proteus vulgaris (ATCC6380)with minimum inhibitory concentrations of 1.25 mg/mLcompared to oleanolic acid (2.5 mg/mL). Compounds 13 and 14 displayed significant cytotoxic effectsin vitro against the cancer cell lines (MCF-7 and DU 145) compared to the oleanolic acid (IC50 ˃ 200 µM).

CONCLUSION

The present study revealed that the modification of C28 of OA enhanced its biological properties.

Quorum sensing modulatory and biofilm inhibitory activity of Plectranthus barbatus essential oil: a novel intervention strategy

The essential oil (EO) from the roots of Plectranthus barbatus Andr. (Syn. Coleus forskohlii Briq.) was evaluated for quorum sensing (QS) inhibitory activity. P. barbatus EO was screened for inhibition of QS regulated violacein production in Chromobacterium violaceum (ATCC 12472) wild-type strain. At inhibitory (6.25% v/v) and sub-inhibitory concentrations (3.125% v/v) of the EO, dose-dependent response in the inhibition of violacein production was observed in C. violaceum. Similarly, sub-MIC (6.25% v/v) of P. barbatus EO disrupted QS regulated biofilm formation by 27.87% and inhibited swarming and twitching motility in Pseudomonas aeruginosa PA01 implying its anti-infective and QS modulatory activity. Fluorescence microscopy studies confirmed the disruption of biofilm formation by EO in P. aeruginosa PAO1. Promising antibacterial activity was recorded at concentrations as low as 3.12% v/v for Listeria monocytogenes (ATCC 13932) and at 6.25% v/v for both Salmonella enterica subsp. enterica serovar Typhimurium (ATCC 25241) and Escherichia coli (ATCC 11775). Furthermore, significant dose-dependent inhibition was observed for biofilm formation and motility in all the tested pathogens in different treated concentrations. GC-MS analysis revealed α-pinene, endo-borneol, bornyl acetate, 1-Hexyl-2-Nitrocyclohexane as the major phytoconstituents. P. barbatus EO or its constituent compounds with QS modulatory, antimicrobial and biofilm inhibitory property could be potential new-age dietary source based intervention and preservation technologies.

Quorum sensing-regulated functions of Serratia marcescens are reduced by eugenol

Background and Objectives

Serratia marcescens has emerged as a nosocomial pathogen responsible for human infections, where antibiotic resistance further complicates the treatments. In S. marcescens, biofilm formation and virulence factor production are controlled via quorum sensing (QS) system. QS is a signaling system that enables gene regulation to control diverse physiological functions in bacteria. Essential oils have shown to be potential in diminishing the pathogenicity and virulence of drug-resistant bacteria. This study was performed to determine whether eugenol would affect QS system, biofilm formation and virulence factor production of S. marcescens.

Materials and Methods

Biofilm formation, extracellular virulence factor production (hemolysin and protease), swarming motility and pigment formation of S. marcescens ATCC 13880 and S. marcescens Sm2 were assessed after eugenol exposure at 1.25 and 2.5 µg/ml concentrations. The expression of genes involved in motility (flhD), attachment (fimC), biofilm formation (bsmB, bsmA), and QS regulatory (swrR) were also evaluated.

Results

Eugenol treatment at 1.25 and 2.5 µg/ml concentrations caused a significant reduction in biofilm formation. The pigment, hemolysin and protease production of two studied S. marcescens strains, also reduced significantly by eugenol treatments (p<0.05). The bsmA, bsmB, flhD and fimC genes were down-regulated after eugenol treatment. The swrR gene expression was also reduced significantly by eugenol in both S. marcescens strains (p<0.05).

Conclusion

Eugenol inhibited quorum sensing-regulated functions of two studied S. marcescens strains.

Antibacterial Activity and Anti-Quorum Sensing Mediated Phenotype in Response to Essential Oil from Melaleuca bracteata Leaves

The prominent antibacterial and quorum sensing (QS) inhibition activity of aromatic plants can be used as a novel intervention strategy for attenuating bacterial pathogenicity. In the present work, a total of 29 chemical components were identified in the essential oil (EO) of Melaleuca bracteata leaves by gas chromatography-mass spectrometry (GC-MS). The principal component was methyleugenol, followed by methyl trans-cinnamate, with relative contents of 90.46% and 4.25%, respectively. Meanwhile, the antibacterial activity and the QS inhibitory activity of M. bracteata EO were first evaluated here. Antibacterial activity assay and MIC detection against seven pathogens (Dickeya dadantii Onc5, Staphylococcus aureus ATCC25933, Pseudomonas spp., Escherichia coli ATCC25922, Serratia marcescens MG1, Pseudomonas aeruginosa PAO1 and Chromobacterium violaceum ATCC31532) demonstrated that S. aureus ATCC25933 and S. marcescens MG1 had the higher sensitivity to M. bracteata EO, while P. aeruginosa PAO1 displayed the strongest resistance to M. bracteata EO. An anti-QS (anti-quorum sensing) assay revealed that at sub-minimal inhibitory concentrations (sub-MICs), M. bracteata EO strongly interfered with the phenotype, including violacein production, biofilm biomass, and swarming motility, as well as N-hexanoyl-L-homoserine lactone (C6-HSL) production (i.e., a signaling molecule in C. violaceum ATCC31532) of C. violaceum. Detection of C6-HSL indicated that M. bracteata EO was capable of not only inhibiting C6-HSL production in C. violaceum, but also degrading the C6-HSL. Importantly, changes of exogenous C6-HSL production in C. violaceum CV026 revealed a possible interaction between M. bracteata EO and a regulatory protein (cviR). Additionally, quantitative real-time polymerase chain reaction (RT-qPCR) analysis demonstrated that the expression of QS-related genes (cviI, cviR, vioABCDE, hmsNR, lasA-B, pilE1, pilE3, and hcnB) was significantly suppressed. Conclusively, these results indicated that M. bracteata EO can act as a potential antibacterial agent and QS inhibitor (QSI) against pathogens, preventing and controlling bacterial contamination.

Anti quorum sensing and anti virulence activity of tannic acid and it's potential to breach resistance in Salmonella enterica Typhi / Paratyphi A clinical isolates

Salmonella enterica Typhi and Paratyphi A are food borne pathogens causing typhoid, which is one of the most important food borne disease in the developing world. S. Typhi and S. Paratyphi A are of much concern as multi drug resistance has been on the rise. The current study is aimed to screen phytochemicals for anti quorum sensing (QS) activity against S. Typhi and S. Paratyphi A. Upon screening with swarming assay, tannic acid (TA) showed highest anti-QS activity with minimal concentration of 400μg/ml. The anti-QS activity of TA was confirmed with C. violaceum ATCC 12,472. TA showed 38-43% and 35-50% of inhibition in cell surface hydrophobicity and EPS production respectively. Through FTIR analysis, it has been observed that EPS of treated cells has a considerable change in protein and peptide. TA has also exhibited drastic reduction in the surfactant production as high as 85-90%. Blood sensitivity and antibiotic sensitivity assay revealed that TA significantly sensitizes the S. Typhi and S. Paratyphi A cells to immune components in human blood and antibiotics. It has reduced the resistance of S. Typhi and S. Paratyphi A cells against amikacin, ampicillin, ciprofloxacin, azithromycin, chloramphenicol and gentamycin, thus revitalized the usage of these antibiotics against drug resistant S. Typhi and S. Paratyphi A infections. The consistency of anti-QS potential of TA was further evaluated and established with another eight clinical isolates of S. Typhi and S. Paratyphi A. Thus TA has been proved as a promising anti QS agent that can be developed as a therapeutic combination against S. Typhi and S. Paratyphi A.

Anti-quorum sensing activity of Forsythia suspense extract against Chromobacterium violaceum by targeting CviR receptor

The increasing incidence of antimicrobial-resistant bacterial pathogens has focused researchers on quorum sensing inhibition strategies instead of those conventional approaches to fight bacterial infections. Anti-quorum sensing (QS) activity of aqueous extract from Forsythia suspense (FSE) was assessed, and its potential QS inhibition mechanisms were also analyzed. The minimal inhibitory concentration (MIC) of FSE to Chromobacterium violaceum 12472 is 0.5 mg mL^-1. Inhibition of QS-regulated violacein production and biofilm formation in C. violaceum 12472 by FSE occurred in a concentration-dependent manner at sub-MIC, with > 70.12 and > 85.31% inhibition at 0.25 mg mL^-1, respectively. N-Acyl homoserine lactones (AHLs) extracted from cultures of C. violaceum 31532 grown in the presence of FSE could not change the violacein production in C. violaceum 026, which indicated that FSE did not inhibit AHL synthesis. We also found that FSE cannot degrade AHLs. Finally, in silico molecular docking was conducted. The computed binding energy data suggested that components of F. suspense have a tendency to inhibit CviR with varying binding affinities and the energy score of Pinoresinol (- 26.02 kcal/mol) is higher than that of C6-HSL (- 16.09 kcal mol^-1). We concluded that FSE acts as an antagonist of bacterial quorum sensing by competing with AHL receptor binding site.

Lonicerin, an anti-algE flavonoid against Pseudomonas aeruginosa virulence screened from Shuanghuanglian formula by molecule docking based strategy

ETHNOPHARMACOLOGICAL RELEVANCE

The Shuanghuanglian formula (SF) is a famous antimicrobial and antiviral traditional Chinese medicine that is made of Lonicera japonica Thunb., Scutellaria baicalensis Georgi, and Forsythia suspensa (Thunb.) Vahl. According to the Chinese Pharmacopoeia, the SF is commonly administered in the forms of oral liquid, tablets, and injection. It has long been used to treat acute respiratory tract infections, especially lung infection.

AIM OF THE STUDY

In the light of the increasing incidence of multidrug resistance to conventional antibiotics, the aim of this study was to screen potential anti-virulence agents against Pseudomonas aeruginosa from the extract of the SF.

MATERIALS AND METHODS

The SF was used for effective compounds screening via the combination of the molecule docking approach and ultra-high-performance liquid chromatography-quadrupole/time of flight mass spectrometry. Fifty-one anti-virulence-related proteins were docked, 26 identified compounds were from SF. Subsequently, the top-scoring screened compound was assessed via bioactive-related assays, including the quantification of alginate biosynthesis, anti-biofilm assays, and the A549 human lung cells infection.

RESULT

A flavonoid Lonicerin was found to be bonded with the active site of the alginate secretion protein (AlgE) with the highest score in molecule docking. Furthermore, we validated that Lonicerin could significantly reduce alginate secretion (25 μg/mL) and biofilm formation (12.5 μg/mL) at a sub-MIC concentration without inhibiting the proliferation of P. aeruginosa or influencing the expression of AlgE, which suggested that Lonicerin may directly inhibit AlgE. In addition, Lonicerin was proven to inhibit the infection of P. aeruginosa in the A549 cells.

CONCLUSION

This work reported on the first potential AlgE antagonist that was derived from herbal resources. Lonicerin was proven to be an effective inhibitor in-vitro of P. aeruginosa infection.

Essential oils of Origanum compactum increase membrane permeability, disturb cell membrane integrity, and suppress quorum-sensing phenotype in bacteria

The aim of this study was to investigate antibacterial activity of Origanum compactum essential oils collected at three phenological stages on Escherichia coli and Bacillus subtilis. The antibacterial activity was evaluated using the agar-well diffusion assay. The MIC and MBC values were determined using the micro-dilution assay. The investigation of the antibacterial action was carried out by the evaluation of the effect of O. compactum essential oils on the antibacterial kinetic growth, the integrity of cell membrane and permeability of the cell membrane. The anti-quorum sensing activity was tested by the inhibition of the biofilm formation. The findings of this study showed that O. compactum essential oil has potent antibacterial activities against E. coli and B. subtilis. The lowest inhibition value against B. subtilis was obtained with O. compactum essential oil at the post-flowering stage (MIC = MBC = 0.0312% (v/v)). The antibacterial mechanisms of O. compactum essential oils are related to the disturbing of the cell membrane integrity and the increasing of the membrane permeability, which leads to the leakage of genetic materials (DNA and RNA). Moreover, O. compactum essential oils inhibited the formation of the biofilms, a phenotype that has been known to be quorum sensing regulated.

Inhibitive Effect of Eugenol and Its Nanoemulsion on Quorum Sensing-Mediated Virulence Factors and Biofilm Formation by Pseudomonas aeruginosa

The aim of the present study was to evaluate the quorum sensing (QS) inhibition potential of eugenol and eugenol nanoemulsion against QS-dependent virulence factor production and gene expression, as well as biofilm formation in Pseudomonas aeruginosa. In the current study, eugenol nanoemulsion at a sub-MIC of 0.2 mg/mL specifically inhibited about 50% of the QS-mediated violacein production in Chromobacterium violaceum, as well as the production of N-(3-oxododecanoyl)-l-homoserine lactone (3-oxo-C₁₂-HSL) and C₄-HSL N-acyl homoserine lactone signal molecules, pyocyanin, and swarming motility in P. aeruginosa. The inhibitive effect of eugenol and its nanoemulsion on the expression of the QS synthase genes was concentration dependent, displaying 65 and 52% expression level for lasI, respectively, and 61 and 45% expression level for rhlI, respectively, at a concentration of 0.2 mg/mL. In addition, the inhibitive effect of eugenol and its nanoemulsion on the expression of the rhlA gene responsible for the production of rhamnolipid was also concentration dependent, displaying 65 and 51% expression level for the rhlA gene, respectively, at a concentration of 0.2 mg/mL. Eugenol and its nanoemulsion also displayed 36 and 63% respective inhibition of biofilm formation by P. aeruginosa at the 0.2 mg/mL concentration. Therefore, the nanoemulsion could be used as a novel QS-based antibacterial and antibiofilm agent for the control of harmful bacteria.

Quorum sensing inhibitors as antipathogens: biotechnological applications

The mechanisms through which microbes communicate using signal molecules has inspired a great deal of research. Microbes use this exchange of information, known as quorum sensing (QS), to initiate and perpetuate infectious diseases in eukaryotic organisms, evading the eukaryotic defense system by multiplying and expressing their pathogenicity through QS regulation. The major issue to arise from such networks is increased bacterial resistance to antibiotics, resulting from QS-dependent mediation of the formation of biofilm, the induction of efflux pumps, and the production of antibiotics. QS inhibitors (QSIs) of diverse origins have been shown to act as potential antipathogens. In this review, we focus on the use of QSIs to counter diseases in humans as well as plants and animals of economic importance. We also discuss the challenges encountered in the potential applications of QSIs.

Virtual Screening and Biomolecular Interactions of CviR-Based Quorum Sensing Inhibitors Against Chromobacterium violaceum

The rise of bacterial multi drug resistance becomes a global threat to the mankind. Therefore it is essential to find out alternate strategies to fight against these "super bugs." Quorum sensing (QS) is a cell-to-cell communication mechanism by which many bacteria regulate their biofilm and virulence factors expression to execute their pathogenesis. Hence, interfering the quorum sensing is an effective alternate strategy against various pathogens. In this study, we aimed to find out potential CviR-mediated quorum sensing inhibitors (QSIs) against Chromobacterium violaceum. Virtual screening from a natural products database, in vitro biofilm and violacein inhibition assays have been performed. Biofilm formation was investigated using confocal microscopy and gene expression studies were carried out using qRT-PCR. Further, to study the biomolecular interaction of QSIs with purified CviR Protein (a LuxR homologue), microscale thermophoresis (MST) analysis was performed. Results suggested that phytochemicals SPL, BN1, BN2, and C7X have potential GScore when compared to cognate ligand and reduced the biofilm formation and violacein production significantly. Especially, 100 μM of BN1 drastically reduced the biofilm formation about 82.61%. qRT-PCR studies revealed that cviI, cviR, vioB, vioC, vioD genes were significantly down regulated by QSIs. MST analysis confirmed the molecular interactions between QSIs and purified CviR protein which cohere with the docking results. Interestingly, we found that BN2 has better interaction with CviR (Kd = 45.07 ±1.90 nm). Overall results suggested that QSIs can potentially interact with CviR and inhibit the QS in a dose dependent manner. Since, LuxR homologs present in more than 100 bacterial species, these QSIs may be developed as broad spectrum anti-infective drugs in future.

Nontargeted metabolomics approach to determine metabolites profile and antioxidant study of Tropical Almond (Terminalia catappa L.) fruit peels using GC-QTOF-MS and LC-QTOF-MS

The objective of the present study was to identify the metabolome pattern and study the biological efficacy of Almond (Terminalia catappa L.) peels. In the present study, metabolite profiling was carried out using GC-QTOF-MS and LC-QTOF-MS techniques, from the potent extract showed highest antioxidant efficacy. Antioxidant efficacy of the various extracts derived by six different extraction methods was assessed by different assays viz. 2,2-diphenyl-1-picrylhydrazyl, superoxide, 2,2'-Azino-bis-(3-ethyl)benzothiazoline)-6-sulfonic acid diammonium salt radical cation inhibition assays and ferric reducing antioxidant power. The methanolic maceration extract showed significant antioxidant activity in all assays and richest source of flavonoid content. The results showed that the extraction method significantly altered the antioxidant activity. The correlation between the antioxidant activities and total flavonoid content were ranging between 0.939 to 0.628. Methanolic maceration extraction method proved to be the best extraction method for the extraction of antioxidant. During the metabolite profiling employed by GC-QTOF-MS and LC-QTOF-MS and total 24 and 53 compounds belongs to different groups were detected and identified, will help to uncover the relation with potent antioxidant activity.

Screening of Natural Product Derivatives Identifies Two Structurally Related Flavonoids as Potent Quorum Sensing Inhibitors against Gram-Negative Bacteria

Owing to the failure of conventional antibiotics in biofilm control, alternative approaches are urgently needed. Inhibition of quorum sensing (QS) represents an attractive target since it is involved in several processes essential for biofilm formation. In this study, a compound library of natural product derivatives (n = 3040) was screened for anti-quorum sensing activity using Chromobacterium violaceum as reporter bacteria. Screening assays, based on QS-mediated violacein production and viability, were performed in parallel to identify non-bactericidal QS inhibitors (QSIs). Nine highly active QSIs were identified, while 328 compounds were classified as moderately actives and 2062 compounds as inactives. Re-testing of the highly actives at a lower concentration against C. violaceum, complemented by a literature search, led to the identification of two flavonoid derivatives as the most potent QSIs, and their impact on biofilm maturation in Escherichia coli and Pseudomonas aeruginosa was further investigated. Finally, effects of these leads on swimming and swarming motility of P. aeruginosa were quantified. The identified flavonoids affected all the studied QS-related functions at micromolar concentrations. These compounds can serve as starting points for further optimization and development of more potent QSIs as adjunctive agents used with antibiotics in the treatment of biofilms.

Exploring the anti-quorum sensing activity of a d-limonene nanoemulsion for Escherichia coli O157:H7

In this study, a d-limonene nanoemulsion was developed by using a spontaneous emulsification method and its potential to inhibit the quorum sensing (QS)-regulated properties of Escherichia coli O157:H7 (E. coli) were revealed. The results in this study showed that d-limonene nanoemulsion inhibited E. coli biofilm formation through the suppression of curli and extracellular polymeric substance (EPS) production without inhibiting cell growth, and decreased swimming and swarming ability. Further analyses showed that d-limonene nanoemulsion interfered with auto-inducer 2 (AI-2) communication and repressed the expression of curli related genes and AI-2 importer genes in E. coli. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 1979-1986, 2018.

Thymoquinone Inhibits Virulence Related Traits of Cronobacter sakazakii ATCC 29544 and Has Anti-biofilm Formation Potential

The aim of this study was to determine whether thymoquinone, the principal active ingredient in the volatile oil of Nigella sativa seeds, could suppress certain virulence traits of Cronobacter sakazakii ATCC 29544 which contribute to infection. Sub-inhibitory concentrations of thymoquinone significantly decreased motility, quorum sensing, and endotoxin production of C. sakazakii ATCC 29544 and biofilm formation of C. sakazakii 7-17. Thymoquinone substantially reduced the adhesion and invasion of C. sakazakii ATCC 29544 to HT-29 cells and decreased the number of intracellular bacterial cells within the RAW 264.7 macrophage cells. Thymoquinone also repressed the transcription of sixteen genes involved in the virulence. These findings suggest that thymoquinone could attenuated virulence-related traits of C. sakazakii ATCC 29544, and its effects on other C. sakazakii strains and in vivo C. sakazakii infection need further investigation.

Anti-bacterial, free radical scavenging activity and cytotoxicity of acetone extracts of Grewia flava

Background

Bacterial infections of the gastrointestinal tract (GIT) cause vomiting, diarrhoea and even systemic disease. There is a need for the development of natural products into alternative and safer medicines.

Objectives

This study evaluated the anti-microbial activity of extracts prepared from berries, leaves, bark and roots of the edible plant Grewia flava.

Methods

The anti-bacterial activity was evaluated by the broth microdilution method. Anti-oxidant activity of the most active extracts was performed by 2, 2-diphenyl-1-picrylhydrazyl (DPPH) assay. The cytotoxicity of the extracts was determined using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay.

Results

The acetone extracts of the leaves and roots showed the best activity with MIC values as low as 0.03 mg/mL against Staphylococcus aureus and Salmonella typhimurium and 0.07 mg/mL against Bacillus cereus, Escherichia coli and Staphylococcus aureus. Quantitative analysis of the scavenging ability showed that acetone extracts exhibited good free radical scavenging activity in a dose-dependent manner. The berries extract had the highest LC₅₀ (lowest toxicity) of 551.68 68 µg/mL.

Conclusion

Acetone extract of leaves and roots of Grewia flava contain anti-microbial and anti-oxidant compounds and could therefore be used as a natural product with little toxicity to host cells.

Inhibition of Cronobacter sakazakii Virulence Factors by Citral

Cronobacter sakazakii is a foodborne pathogen associated with fatal forms of necrotizing enterocolitis, meningitis and sepsis in neonates and infants. The aim of this study was to determine whether citral, a major component of lemongrass oil, could suppress putative virulence factors of C. sakazakii that contribute to infection. Sub-inhibitory concentrations of citral significantly decreased motility, quorum sensing, biofilm formation and endotoxin production. Citral substantially reduced the adhesion and invasion of C. sakazakii to Caco-2 cells and decreased bacterial survival and replication within the RAW 264.7 macrophage cells. Citral also repressed the expression of eighteen genes involved in the virulence. These findings suggest that citral has potential to be developed as an alternative or supplemental agent to mitigate the infections caused by C. sakazakii.

Proposed mechanisms of Terminalia catappa in hyperglycaemia and associated diabetic complications

Objectives

Terminalia catappa has shown potent antidiabetic activity in the past; however, the exact molecular mechanisms by which it acts have not been elucidated. This review aims at exploring several hypotheses which have been proposed to explain its mechanism of action, including reduction in oxidative stress, inflammation, angiogenesis, lipid profile correction and direct hypoglycaemic actions.

Methods

A thorough review of all the articles, research as well as reviews, available regarding the concerned topic was performed. MEDLINE databases were searched using keywords (and their combinations), such as T. catappa, renin oxidative stress, inflammation, angiogenesis, diabetic retinopathy, α-glucosidase and α-amylase, among several others. English-language articles were preferably selected.

Key findings

Apart from metabolic dysfunctions, several hyperglycaemia-induced pathological conditions come into scene as the after-effects of diabetes. These mainly include inflammation, oxidative stress, angiogenesis and lipid profile alteration, which ultimately result in vascular endothelial dysfunction, hepatic steatosis, lipid peroxidation and apoptosis of endothelial, hepatic and neuronal cells. Terminalia catappa effectively attenuates the progression of diabetic retinopathy and shows significant hypoglycaemic actions. The mechanisms behind these effects were explained.

Conclusion

Terminalia catappa may provide an effective natural product to treat hyperglycaemia and prevent subsequent diabetic complications.

Flavones as Quorum Sensing Inhibitors Identified by a Newly Optimized Screening Platform Using Chromobacterium violaceum as Reporter Bacteria

Quorum sensing (QS) is the process by which bacteria produce and detect signal molecules to coordinate their collective behavior. This intercellular communication is a relevant target for anti-biofilm therapies. Here we have optimized a screening-applicable assay to search for new quorum sensing inhibitors from natural compound libraries. In this system, QS is correlated with the production of violacein, which is directly controlled by the LuxI/LuxR system in Chromobacterium violaceum ATCC 31532. The parallel use of C. violaceum Tn5-mutant CV026, which depends on auto-inducer addition, allows simultaneous discrimination of compounds that act as quenchers of the AHL signal (quorum quenchers). The incorporation of a redox stain into the platform allowed further distinction between QS inhibitors, quorum quenchers and antibacterial compounds. A pilot screening was performed with 465 natural and synthetic flavonoids. All the most active compounds were flavones and they displayed potencies (IC₅₀) in the range of 3.69 to 23.35 μM. These leads were particularly promising as they inhibited the transition from microcolonies into mature biofilms from Escherichia coli and Pseudomonas aeruginosa strains. This approach can be very effective in identifying new antimicrobials posing lesser risks of resistance.

Quorum Sensing Inhibiting Activity of Streptomyces coelicoflavus Isolated from Soil

Quorum sensing (QS) systems communicate bacterial population and stimulate microbial pathogenesis through signaling molecules. Inhibition of QS signals potentially suppresses microbial infections. Antimicrobial properties of Streptomyces have been extensively studied, however, less is known about quorum sensing inhibitory (QSI) activities of Streptomyces. This study explored the QSI potential of Streptomyces isolated from soil. Sixty-five bacterial isolates were purified from soil samples with morphological characteristics of Streptomyces. The three isolates: S6, S12, and S17, exhibited QSI effect by screening with the reporter, Chromobacterium violaceum. Isolate S17 was identified as Streptomyces coelicoflavus by sequencing of the hypervariable regions (V1-V6) of 16S rRNA and was assigned gene bank number KJ855087. The QSI effect of the cell-free supernatant of isolate S17 was not abolished by proteinase K indicating the non-enzymatic activity of QSI components of S17. Three major compounds were isolated and identified, using spectroscopic techniques (1D, 2D NMR, and Mass spectrometry), as behenic acid (docosanoic acid), borrelidin, and 1H-pyrrole-2-carboxylic acid. 1H-pyrrole-2-carboxylic acid inhibited QS and related virulence factors of Pseudomonas aeruginosa PAO1 including; elastase, protease, and pyocyanin without affecting Pseudomonas viability. At the molecular level, 1H-pyrrole-2-carboxylic acid suppressed the expression of QS genes (lasI, lasR, lasA, lasB, rhlI, rhlR, pqsA, and pqsR). Moreover, QSI activity of S17 was assessed under different growth conditions and ISP2 medium supplemented with glucose 0.4% w/v and adjusted at pH 7, showed the highest QSI action. In conclusion, 1H-pyrrole-2-carboxylic acid, one of the major metabolites of Streptomyces isolate S17, inhibited QS and virulence determinants of P. aeruginosa PAO1. The findings of the study open the scope to exploit the in vivo efficacy of this active molecule as anti-pathogenic and anti-virulence of P. aeruginosa.

Broad Spectrum Anti-Quorum Sensing Activity of Tannin-Rich Crude Extracts of Indian Medicinal Plants

Quorum sensing (QS) mechanisms have been demonstrated to have significance in expression of pathogenicity in infectious bacteria. In Gram negative bacteria the autoinducer molecules that mediate QS are acyl homoserine lactones (AHL) and in Gram positive bacteria they are peptides called autoinducing peptides (AIP). A screening of tannin-rich medicinal plants was attempted to identify extracts that could interrupt the QS mechanisms in both Gram positive and Gram negative bacteria over a wide range of concentrations and therefore potentially be potent agents that could act as broad spectrum QS inhibitors. Six out of the twelve Indian medicinal plant extracts that were analyzed exhibited anti-QS activity in Chromobacterium violaceum 12472 and in S. aureus strain with agr:blaZ fusion over a broad range of subinhibitory concentrations, indicating that the extracts contain high concentration of molecules that can interfere with the QS mechanisms mediated by AHL as well as AIP.

Tannin-Rich Fraction from Pomegranate Rind Inhibits Quorum Sensing in Chromobacterium violaceum and Biofilm Formation in Escherichia coli

Pomegranate rind has been found to inhibit numerous pathogens, mostly attributed to its tannin fraction. The present study was conducted to investigate the quorum sensing (QS) inhibition effect of tannin-rich fraction from pomegranate rind (TFPR) by using an indicator strain Chromobacterium violaceum. Meanwhile, its effect on biofilm formation and motility of Escherichia coli was evaluated. It was shown that TFPR inhibited QS-regulated violacein pigment production. Biofilm formation and motility of E. coli were also hindered by TFPR. Transcriptional analysis further showed that TFPR repressed expressions of curli genes (csgB and csgD) and various motility genes (fimA, fimH, flhD, motB, qseB, and qseC). Our findings indicated that TFPR has potential application for controlling E. coli contaminations or biofilms in the food industry.

The quorum-sensing inhibiting effects of stilbenoids and their potential structure-activity relationship

Stilbenoids, known an important phytoalexins in plants, were renowned for their beneficial effects on cardiovascular, neurological and hepatic systems. In the present study, quorum sensing inhibition activity of ten stilbenoids were tested using Chromobacterium violaceum CV026 as the bio-indicator strain and the structure-activity relationship was also investigated. Among them, resveratrol (1), piceatannol (2) and oxyresveratrol (3) showed potential anti-QS activities. At the sub-MIC concentrations, 1-3 demonstrated a statistically significant reduction of violacein in C. violaceum CV026 in a concentration dependent manner. Furthermore, the effects of 1-3 on QS regulated virulence factors in Pseudomonas aeruginosa PAO1 were also evaluated. Our results showed that the stilbenoids 1-3 can markedly decreased the production of pyocyanin and swarming motility of P. aeruginosa PAO1. Further transcriptome analyses showed that 1-3 suppressed the expression of QS-induced genes: lasR, lasI, rhlR and rhlI.

Violacein: Properties and Production of a Versatile Bacterial Pigment

Violacein-producing bacteria, with their striking purple hues, have undoubtedly piqued the curiosity of scientists since their first discovery. The bisindole violacein is formed by the condensation of two tryptophan molecules through the action of five proteins. The genes required for its production, vioABCDE, and the regulatory mechanisms employed have been studied within a small number of violacein-producing strains. As a compound, violacein is known to have diverse biological activities, including being an anticancer agent and being an antibiotic against Staphylococcus aureus and other Gram-positive pathogens. Identifying the biological roles of this pigmented molecule is of particular interest, and understanding violacein's function and mechanism of action has relevance to those unmasking any of its commercial or therapeutic benefits. Unfortunately, the production of violacein and its related derivatives is not easy and so various groups are also seeking to improve the fermentative yields of violacein through genetic engineering and synthetic biology. This review discusses the recent trends in the research and production of violacein by both natural and genetically modified bacterial strains.

Isoprenyl caffeate, a major compound in manuka propolis, is a quorum-sensing inhibitor in Chromobacterium violaceum

The emergence of antibiotic-resistant bacterial pathogens, especially Gram-negative bacteria, has driven investigations into suppressing bacterial virulence via quorum sensing (QS) inhibition strategies instead of bactericidal and bacteriostatic approaches. Here, we investigated several bee products for potential compound(s) that exhibit significant QS inhibitory (QSI) properties at the phenotypic and molecular levels in Chromobacterium violaceum ATCC 12472 as a model organism. Manuka propolis produced the strongest violacein inhibition on C. violaceum lawn agar, while bee pollen had no detectable QSI activity and honey had bactericidal activity. Fractionated manuka propolis (pooled fraction 5 or PF5) exhibited the largest violacein inhibition zone (24.5 ± 2.5 mm) at 1 mg dry weight per disc. In C. violaceum liquid cultures, at least 450 µg/ml of manuka propolis PF5 completely inhibited violacein production. Gene expression studies of the vioABCDE operon, involved in violacein biosynthesis, showed significant (≥two-fold) down-regulation of vioA, vioD and vioE in response to manuka propolis PF5. A potential QSI compound identified in manuka propolis PF5 is a hydroxycinnamic acid-derivative, isoprenyl caffeate, with a [M-H] of 247. Complete violacein inhibition in C. violaceum liquid cultures was achieved with at least 50 µg/ml of commercial isoprenyl caffeate. In silico docking experiments suggest that isoprenyl caffeate may act as an inhibitor of the violacein biosynthetic pathway by acting as a competitor for the FAD-binding pockets of VioD and VioA. Further studies on these compounds are warranted toward the development of anti-pathogenic drugs as adjuvants to conventional antibiotic treatments, especially in antibiotic-resistant bacterial infections.

Effect of tannic and gallic acids alone or in combination with carbenicillin or tetracycline on Chromobacterium violaceum CV026 growth, motility, and biofilm formation

Chromobacterium violaceum is an opportunistic pathogen that causes infections that are difficult to treat. The goal of this research was to evaluate the effect of selected tannins (tannic acid (TA) and gallic acid (GA)) on bacterial growth, motility, antibiotic (carbenicillin, tetracycline) susceptibility, and biofilm formation. Both tannins, particularly TA, impaired bacterial growth levels and swimming motilities at sub-minimum inhibitory concentrations (sub-MICs). In combination with tannins, antibiotics showed increased MICs, suggesting that tannins interfered with antibacterial activity. Sub-MICs of tetracycline or TA alone enhanced biofilm formation of C. violaceum; however, in combination, these compounds inhibited biofilm formation. In contrast, carbenicillin at sub-MICs was effective in inhibiting C. violaceum biofilm formation; however, in combination with lower concentrations of TA or GA, biofilms were enhanced. These results provide insights into the effects of tannins on C. violaceum growth and their varying interaction with antibiotics used to target C. violaceum infections.

Free radical scavenging potential and HPTLC analysis of Indigofera tinctoria linn (Fabaceae)

The objective of this study was to evaluate the free radical scavenging potential and high performance thin layer chromatography (HPTLC) fingerprinting of Indigofera tinctoria (I. tinctoria). Phytochemical analysis was carried out using standard methods, and free radical scavenging activity of the plant was determined using 2,2-diphenyl-1-picrylhydrazy (DPPH), nitric oxide (NO) and superoxide anion ([Formula: see text]) radical scavenging capacities. HPTLC plate was kept in CAMAG TLC Scanner 3 and the Rf values at fingerprint data were recorded by WINCATS software. Aqueous extract of I. tinctoria reliably showed the total phenolics (267.2±2.42 mg/g), flavonoids (75.43±3.36 mg/g) and antioxidants (349.11±8.04 mg/g). The extract was found to have DPPH (52.08%), NO (23.12%) and [Formula: see text] (26.79%) scavenging activities at the concentration of 250 μg/mL and the results were statistically significant compared with ascorbic acid standard (p<0.05). HPTLC results confirmed that the extract contained several potential active components such as phenols, flavonoids, saponins and terpenoids as the slides revealed multi-colored bands of varying intensities. This study confirmed that the plant had multipotential antioxidant and free radicals scavenging activities.