Quorum Quenching and Microbial Control through Phenolic Extract of Eugenia Uniflora Fruits

Evaluation of the Health-Promoting Properties of Selected Fruits

In this study, the health-promoting benefits of different fruits grown in Madeira Island, namely lemon (Citrus limon var. eureka), tangerine (Citrus reticulata var. setubalense), pitanga (Eugenia uniflora var. red), tomato (Solanum lycopersicum var. gordal) and uva-da-serra, an endemic blueberry (Vaccinium padifolium Sm.), were investigated. The phenolic composition (total phenolics and total flavonoids content) and antioxidant capacity (assessed through ABTS and DPPH assays) were measured revealing a high phenolic potential for all fruits, except tomato, while uva-da-serra is particularly rich in flavonoids. In relation to the antioxidant capacity, the highest values were obtained for pitanga and uva-da-serra extracts. The bioactive potential was also assessed through the ability of the extracts to inhibit digestive enzymes linked to diabetes (α-amylase, α- and β-glucosidases) and hypertension (angiotensin-converting enzyme, ACE). The results obtained point to a very high bioactive potential with the selected samples exhibiting very important ACE anti-enzymatic capacities. A statistical analysis of the obtained data reveals a very strong correlation between ABTS and TPC, and a strong contribution of the fruit polyphenols for enzyme inhibition, and thus, presenting high antihypertensive and antidiabetic capacities. Overall, the results obtained clearly show a high bioactive potential of the selected fruits that should be further studied, in terms of specific phenolic composition. Moreover, these results strongly support the valorisation of pitanga seeds usually discarded as a waste, and uva-da-serra, an endemic and wild bush, as potential bioresources of bioactive compounds with impact in human diet.

Germacrone: A Potent Secondary Metabolite with Therapeutic Potential in Metabolic Diseases, Cancer and Viral Infections

Natural products, an infinite reserve of bioactive molecules, will continue to serve humans as an important source of therapeutic agents. Germacrone is a bioactive natural compound found in the traditional medicinal plants of family Zingiberaceae. This multifaceted chemical entity has become a point of focus during recent years due to its numerous pharmacological applications, e.g., anticancer, anti-inflammatory, antiviral, antioxidant, anti-adipogenic, anti-androgenic, antimicrobial, insecticidal, and neuroprotective. Germacrone is an effective inducer of cell cycle arrest and apoptosis in various cancers (breast, brain, liver, skin, prostate, gastric, and esophageal) via modulation of different cell signaling molecules and pathways involved in cancer proliferation. This is the first report highlighting the wide spectrum of pharmacological activities exhibited by germacrone. The reported data collected from various shreds of evidences recommend that this multifaceted compound could serve as a potential drug candidate in the near future.

Phenolic extract of Eugenia uniflora L. and furanone reduce biofilm formation by Serratia liquefaciens and increase its susceptibility to antimicrobials

Serratia liquefaciens is a spoilage microorganism of relevance in the dairy industry because it is psychrotrophic, able to form biofilm, and produces thermoresistant proteases and lipases. Phenolic compounds and furanones have been studied as inhibitors of biofilm formation. In this study, the potential of the pulp phenolic extract of Eugenia uniflora L. orange fruits, also called pitanga, and furanone C30 on the inhibition of biofilm formation by S. liquefaciens L53 and the susceptibility to different antimicrobials were evaluated. The pulp phenolic extract of pitanga had a high total phenolic content, being mainly composed of glycosylated quercetins and ellagitannins. Sub-inhibitory concentrations of this extract and furanone reduced biofilm formation by S. liquefaciens on polystyrene and the amount of polysaccharides, proteins and extracellular DNA in the biofilms. These biofilms were also more susceptible to kanamycin. The combinations of furanone with phenolic extract of pitanga or kanamycin showed a synergistic effect with total growth inhibition of S. liquefaciens.

3-Benzyl-Hexahydro-Pyrrolo[1,2-a]Pyrazine-1,4-Dione Extracted From Exiguobacterium indicum Showed Anti-biofilm Activity Against Pseudomonas aeruginosa by Attenuating Quorum Sensing

Bacterial cell-to-cell communication promotes biofilm formation and can potentially lead to multidrug resistance development. Quorum sensing inhibition (QSI) is an effective and widely employed strategy against biofilm formation. The extract from Exiguobacterium indicum SJ16, a gram-positive bacterium, isolated from the rhizosphere of Cyperus laevigatus showed significant anti-quorum sensing activity (about 99%) against the reference Chromobacterium violaceum CV026 strain without exerting any antibacterial effect. The potentially active QSI compound identified in the SJ16 extract was 3-Benzyl-hexahydro-pyrrolo[1, 2-a]pyrazine-1,4-dione. The SJ16 extract containing this active compound showed significant anti-quorum sensing activity against a model quorum sensing bacterium strain Pseudomonas aeruginosa PAO1 and a clinical isolate P. aeruginosa PAH by preventing biofilm formation without attenuating the cell growth within the biofilm. More specifically, the SJ16 extract changed the topography and architecture of the biofilm, thus preventing bacterial adherence and further development of the biofilm. Furthermore, it decreased virulence factors (rhamnolipid and pyocyanin), the bacterial motility, as well as the elastase, and protease activities in P. aeruginosa. Microarray analysis revealed the differential expression of quorum sensing regulatory genes. Based on these results, we herein propose a hypothetical model, characterizing the role of this QSI agent in the transcriptional regulation of quorum sensing in P. aeruginosa PAO1, demonstrating that this compound has significant drug-development potential. Further research is required to delineate its possible applications in therapeutics in the context of biofilm forming bacterial infections.

Effect of Capsicum Frutescens Extract, Capsaicin, and Luteolin on Quorum Sensing Regulated Phenotypes

Capsicum peppers have not been investigated as sources of quorum sensing (QS) inhibitors. This study aimed to identify compounds in pimenta-malagueta (Capsicum frutescens) and red pepper (Capsicum annuum) extracts and to evaluate their effect on violacein production in Chromobacterium violaceum ATCC 12472 and C. violaceum CV026, as well as biofilm formation (BF) in Pseudomonas aeruginosa PAO1 and Serratia marcescens MG1. Among the extracts, pimenta-malagueta methanolic extract (PMME) was chosen because it contained capsaicin, dihydrocapsaicin, and luteolin in greater amount than the other extracts. In general, PMME partially inhibited bacterial growth at 2.5 and 5.0 mg/mL, as well as capsaicin at 100 µg/mL and luteolin at 62.5, 125, and 250 µg/mL. At lower concentrations, PMME and luteolin reduced violacein production in C. violaceum ATCC 12472 without affecting growth, a result that was not observed with capsaicin. We show that violacein inhibition by PMME is likely due to luteolin. In silico docking evaluation showed that luteolin binds to the CviR QS regulator. Crystal violet staining and confocal microscopy revealed that BF was increased by PMME and capsaicin, being remarkably superior for P. aeruginosa PAO1 at 30 °C. Capsaicin is not an effective QS inhibitor, while luteolin should be further investigated for its potential effects in QS regulated phenotypes. PRACTICAL APPLICATION: Quorum sensing (QS) is a form of bacterial communication targeted for studies aiming to inhibit bacterial virulence. QS regulates phenotypes that influence microbial activities across many areas, including Food Science. Capsicum frutescens is a type of chili pepper consumed in Brazil, rich in bioactive compounds such as capsaicin (which gives its pungency) and luteolin (a phenolic compound). We show that C. frutescens extract and luteolin inhibit QS in a model bacterium, along with the possible molecular mechanism of inhibition. Capsaicin did not inhibit QS neither biofilm formation. Luteolin should be further investigated for its QS inhibition properties and biotechnological applications.

Virtual screening of plant compounds and nonsteroidal anti-inflammatory drugs for inhibition of quorum sensing and biofilm formation in Salmonella

Salmonella belongs to the Enterobacteriaceae family which is widely distributed in the environment due to its adaptive capacity to stress conditions. In addition, Salmonella is able to perform a type of cell-to-cell communication called quorum sensing, which leads to differential gene expression. The quorum sensing system mediated by AI-1, acyl homoserine lactones (AHLs), is incomplete in Salmonella because the luxI homolog gene, which encodes for AI-1 synthase, is missing in the genome. However, a homologue of LuxR, known as SdiA, is present and allows the detection of signaling molecules produced by other species of bacteria, leading to regulation of gene expression, mainly related to virulence and biofilm formation. Thus, in view of the importance of quorum sensing on the physiology regulation of microorganisms, the aim of the present study was to perform a virtual screening of plant compounds and nonsteroidal anti-inflammatory drugs (NASIDs) for inhibition of quorum sensing by molecular docking and biofilm formation in Salmonella. In general, most plant compounds and all NSAIDs bound in, at least, one of the three modeled structures of SdiA proteins of Salmonella Enteritidis PT4 578. In addition, many tested compounds had higher binding affinities than the AHLs and the furanones which are inducers and inhibitors of quorum sensing, respectively. The Z-phytol and lonazolac molecules were good candidates for the in vitro inhibition tests of quorum sensing mediated by AI-1 and biofilm formation in Salmonella. Thus, this study directs future prospecting of plant extracts for inhibition of quorum sensing mechanism depending on AHL and biofilm formation. In addition, the use of inhibitors of quorum sensing and biofilm formation can be combined with antibiotics for better treatment efficacy, as well as the use of these compounds to design new drugs.

The Effects of Chinese Herbal Medicines on the Quorum Sensing-Regulated Virulence in Pseudomonas aeruginosa PAO1

The quorum sensing (QS) system has been used by many opportunistic pathogenic bacteria to coordinate their virulence determinants in relation to cell-population density. As antibiotic-resistant bacteria are on the rise, interference with QS has been regarded as a novel way to control bacterial infections. As such, many plant-based natural products have been widely explored for their therapeutic roles. These natural products may contain anti-QS compounds that could block QS signals generation or transmission to combat QS pathogens. In this study, we report the anti-QS activities of four different Chinese herbal plant extracts: Poria cum Radix pini, Angelica dahurica, Rhizoma cibotii and Schizonepeta tenuifolia, on Pseudomonas aeruginosa PAO1. All the plants extracted using hexane, chloroform and methanol were tested and found to impair swarming motility and pyocyanin production in P.aeruginosa PAO1, particularly by Poria cum Radix pini. In addition, all the plant extracts also inhibited violacein production in C.violaceum CV026 up to 50% while bioluminescence activities were reduced in lux-based E. coli biosensors, pSB401 and pSB1075, up to about 57%. These anti-QS properties of the four medicinal plants are the first documentation that demonstrates a potential approach to attenuate pathogens’ virulence determinants.

Leaf Extracts of Selected Gardening Trees Can Attenuate Quorum Sensing and Pathogenicity of Pseudomonas aeruginosa PAO1

An increasing concern on resistance to multiple-antibiotics has led to the discovery of novel agents and the establishment of new precaution strategy. Numerous plant sources have been widely studied to reduce virulence of pathogenic bacteria by interfering cell-to-cell based communication called quorum sensing (QS). Leaf extracts of 17 gardening trees were collected and investigated for their anti-QS effects using a sensor strain Chromobacterium violaceum CV026. Methanolic extracts of K4 (Acer palmatum), K9 (Acer pseudosieboldianum) and K13 (Cercis chinensis) leaves were selected for further experiments based on their antagonism effect on QS without inhibiting C. violaceum CV026 growth. Subsequently, the leaf extracts on QS-mediated virulence of Pseudomonas aeruginosa PAO1 involved in biofilm formation, motility, bioluminescence, pyocyanin production, QS molecules production, and Caenorhabditis elegans killing activity were evaluated. The biofilm formation ability and swarming motility of P. aeruginosa PAO1 were decreased approximately 50% in the presence of these leaf extracts at a concentration of 1 mg/mL. The expression level of lecA::lux of P. aeruginosa PAO1 and pyocyanin production were also reduced. The three leaf extracts also decreased autoinducer (AI) production in P. aeruginosa PAO1 without direct degradation, suggesting that AI synthesis might have been suppressed by these extracts. The three leaf extracts also showed anti-infection activity in C. elegans model. Taken together, these results suggest that methanolic leaf extracts of K4, K9 and K13 have the potential to attenuate the virulence of P. aeruginosa PAO1.