Anti-quorum sensing activity of medicinal plants in southern Florida

Oxidative DNA damage protective activity, antioxidant and anti-quorum sensing potentials of Moringa oleifera

The aqueous extract of leaf (LE), fruit (FE) and seed (SE) of Moringa oleifera was assessed to examine the ability to inhibit the oxidative DNA damage, antioxidant and anti-quorum sensing (QS) potentials. It was found that these extracts could significantly inhibit the OH-dependent damage of pUC18 plasmid DNA and also inhibit synergistically with trolox, with an activity sequence of LE > FE > SE. HPLC and MS/MS analysis was carried out, which showed the presence of gallic acid, chlorogenic acid, ellagic acid, ferulic acid, kaempferol, quercetin and vanillin. The LE was with comparatively higher total phenolics content (105.04 mg gallic acid equivalents (GAE)/g), total flavonoids content (31.28 mg quercetin equivalents (QE)/g), and ascorbic acid content (106.95 mg/100 g) and showed better antioxidant activity (85.77%), anti-radical power (74.3), reducing power (1.1 ascorbic acid equivalents (ASE)/ml), inhibition of lipid peroxidation, protein oxidation, OH-induced deoxyribose degradation, and scavenging power of superoxide anion and nitric oxide radicals than did the FE, SE and standard alpha-tocopherol. Eventually, LE and FE were found to inhibit violacein production, a QS-regulated behavior in Chromobacterium violaceum 12472.

Chemical composition and antibacterial activity of the essential oils of Callistemon citrinus and Callistemon viminalis from South Africa

The chemical composition and the antibacterial activity of the essential oils obtained by hydrodistillation from the leaves of Callistemon citrinus and Callistemon viminalis were analyzed by GC and GC/MS. Twenty-four and twelve components were identified for C. citrinus and C. viminalis, representing 92.0% and 98.3% of the total oils. The major components of C. citrinus and C. viminalis were 1,8-cineole (61.2% and 83.2%) and α-pinene (13.4% and 6.4%), respectively. The in vitro antibacterial activity of the essential oils was studied against 12 bacteria strains using disc diffusion and broth microdilution methods. The oils exhibited strong zone of inhibitions against some bacteria such as S. faecalis (20.3-24.0 mm), both strains of S. aureus (23.0-26.3 mm), B. cereus (17.3-19.0 mm) and S. macrcesens (11.3-23.7 mm) when compared to standard antibiotics gentamycin and tetracycline used as controls. Expect for P. aeruginosa and S. macrcescens, the MIC values of both essential oils ranged from 0.31-2.50 mg/mL.

Antioxidant and anti-quorum sensing activities of green pod of Acacia nilotica L

The antioxidant and anti-quorum sensing activities of eight extracts were studied in green pods of Acacia nilotica. The specific phenolic compositions and their quantifications were performed by HPLC and MS/MS, which showed that the HEF (pH 4) was higher in gallic acid, ellagic acid, epicatechin, rutin, and GTs. In order to find antioxidant potential of various extracts, their activities were studied for TPC, AOA, FRSA, RP, inhibition of LPO, FIC activity, HO* and O(2)(-) scavenging activities. Among them HEF (pH 4) has shown potent antioxidant activity. HEF (pH 4) was also found effective in protecting plasmid DNA and HAS protein oxidation induced by HO*. Pre-treatment of HEF (pH 4) at 75 and 150 mg/kg body weight for 6 days caused a significant increase in the levels of CAT and SOD and decrease in the level of MDA content in liver, lungs, kidneys and blood when compared to CCl(4)-intoxicated rats. Eventually, the extracts were also screened for anti-QS activity. Of these extracts two showed QS inhibition: HEF (pH 4) and HCE. The results obtained strongly indicate that green pod of A. nilotica are important source of natural antioxidants.

Attenuation of Pseudomonas aeruginosa virulence by medicinal plants in a Caenorhabditis elegans model system

Expression of a myriad of virulence factors and innate antibiotic resistance enables the opportunistic human pathogen Pseudomonas aeruginosa to create intractable infections. Using a nematode model, we screened for novel inhibitors of this pathogen. Aqueous extracts of three plants, Conocarpus erectus, Callistemon viminalis and Bucida buceras, were examined for their effects on P. aeruginosa killing of the nematode Caenorhabditis elegans. The results were evaluated in toxin-based and infection-based assays using P. aeruginosa strains PAO1 and PA14. The tested plant extracts prevented mortality via gut infection in approximately 60 % of the worms and caused a 50-90 % reduction in death from toxin production. All extracts inhibited nematode death by P. aeruginosa without host toxicity, indicating their potential for further development as anti-infectives.

Boesenbergia pandurata (Roxb.) Schltr., Eleutherine americana Merr. and Rhodomyrtus tomentosa (Aiton) Hassk. as antibiofilm producing and antiquorum sensing in Streptococcus pyogenes

Biofilm formation has been demonstrated as a potentially important mechanism contributing to antibiotic treatment failure on Streptococcus pyogenes. It could play a significant role in recurrent and chronic infections. Boesenbergia pandurata (Roxb.) Schltr., Eleutherine americana Merr. and Rhodomyrtus tomentosa (Aiton) Hassk. have been previously reported from our laboratory as effective agents against S. pyogenes. Therefore, in the present study, we observed the effect of these plants on biofilm formation. The bacterial biofilms were quantified by safranin staining and absorbance at 492 nm. The results clearly demonstrated that all subinhibitory concentrations [1/32-1/2 minimal inhibitory concentration (MIC)] of E. americana (7.81-125 microg mL(-1)) and R. tomentosa (0.24-7.81 microg mL(-1)) extracts significantly prevented biofilm formation while 1/2MIC (7.81 microg mL(-1)) of B. pandurata extract produced this effect. The issue of antiquorum sensing of this pathogenic bacterium has been further explored. A correlation between antiquorum-sensing and antibiofilm-producing activities was demonstrated. Strong inhibition on quorum sensing was displayed with the extract of R. tomentosa. Eleutherine americana extract showed partial inhibition, while B. pandurata did not show this activity. By contrast, an assay of microbial adhesion to hydrocarbon revealed no changes in the cell-surface hydrophobicity of the treated organisms. Active organisms with the ability to inhibit quorum sensing and biofilm formation are worth studying as they may provide complimentary medicine for biofilm-associated infections.

Inhibition of quorum sensing-controlled virulence factor production in Pseudomonas aeruginosa by South Florida plant extracts

Quorum sensing (QS) is a key regulator of virulence and biofilm formation in Pseudomonas aeruginosa and other medically relevant bacteria. Aqueous extracts of six plants, Conocarpus erectus, Chamaesyce hypericifolia, Callistemon viminalis, Bucida buceras, Tetrazygia bicolor, and Quercus virginiana, were examined in this study for their effects on P. aeruginosa virulence factors and the QS system. C. erectus, B. buceras, and C. viminalis caused a significant inhibition of LasA protease, LasB elastase, pyoverdin production, and biofilm formation. Additionally, each plant presented a distinct effect profile on the las and rhl QS genes and their respective signaling molecules, suggesting that different mechanisms are responsible for efficacy. Extracts of all plants caused the inhibition of QS genes and QS-controlled factors, with marginal effects on bacterial growth, suggesting that the quorum-quenching mechanisms are unrelated to static or cidal effects.

Inhibition of quorum sensing-regulated behaviors by Scorzonera sandrasica

Many Gram-negative bacteria use N-acyl homoserine lactone signal molecules to monitor their own population density and coordinate gene regulation in a process called quorum sensing (QS). Increasing evidence implies that certain eukaryotes produce QS-inhibitory compounds. In this work, we tested 46 terrestrial plants materials for their ability to inhibit QS-regulated behaviors in different bacterial species. Plant materials were dried and extracted using different solvents. The chloroform-soluble compounds extracted from Scorzonera sandrasica were found to inhibit violacein production, a QS-regulated behavior in Chromobacterium violaceum. In addition, the chloroform extract was also able to inhibit QS-regulated carbapenem antibiotic production in Erwinia carotovora. Because the regulation of many bacterial processes is controlled by QS systems, the finding of natural compounds acting as QS inhibitors suggests an attractive tool to control and handle detrimental infections caused by human, animal, and plant pathogens.

Dietary phytochemicals as quorum sensing inhibitors

Quorum sensing (QS) is a cell density dependent expression of species in bacteria mediated by hormone like compounds called autoinducers (AI). Several processes responsible for successful establishment of bacterial infection are mediated by QS. Inhibition of QS is therefore being considered as a new target for antimicrobial chemotherapy. Dietary phytochemicals are secondary metabolites in plants known to have several health benefits including antimicrobial activity. However, their ability to inhibit QS has never been studied. Our objective was to investigate the effect of sub-lethal concentrations (SLC) of bioactive dietary phytochemical extracts from common dietary fruit, herb and spice extracts on modulating QS mediated by AI in model bioassay test systems. QS inhibition was measured in violacein pigment producing Chromobacterium violaceum O26 (CVO26) and CV 31532 system, mediated by AI known as acylated homeserine lactone (AHL). We also investigated the effect of the sub-lethal concentrations of the extracts on swarming motility of pathogens Escherichia coli (EC)O157:H7 and Pseudomonas aeruginosa (PA-01). Our results indicate that all extracts significantly inhibited quorum sensing. The mechanism of inhibition appeared to be combination of interfering with AHL activity and modulating the synthesis of AHL's. Our results also indicated that various phytochemical extracts which inhibited QS also inhibited swarming of pathogenic bacteria, known to be modulated by QS. The observation that phytochemicals from foods can inhibit QS related processes opens up an exciting new strategy for antimicrobial chemotherapy and lead to the discovery of new category of antibiotics which can overcome the issues related to antimicrobial resistance.

Prospects for plant-derived antibacterials

Can weakly active phytochemicals be combined synergistically to produce new antibacterial treatments?

Interactions between bacteria and eukaryotes via small molecules

The interactions that occur between eukaryotes and bacteria have long been of interest, as knowledge of these processes could lead to the development of novel therapeutics and other potential applications in biotechnology. Many of these interactions are mediated by small molecules, which have subsequently formed the focus of numerous studies. An arsenal of small molecules exhibiting a wide range of activities has been isolated from various sources, including plants, animals and microorganisms. As a number of these compounds are pharmacologically active, there is a strong continued interest in natural product chemistry. Recent developments in this field have focused on two areas: evidence has been gathered to show that secondary metabolites are often produced by symbiotic bacteria, rather than by the eukaryotic host, and the importance of bacterial cell-to-cell signalling in bacteria-host interactions has been confirmed.