Effect of Quercetin Rich Onion Extracts on Bacterial Quorum Sensing

Abstract

Quorum sensing (QS) regulates bacterial gene expression and studies suggest quercetin, a flavonol found in onion, as a QS inhibitor. There are no studies showing the anti-QS activity of plants containing quercetin in its native glycosylated forms. This study aimed to evaluate the antimicrobial and anti-QS potential of organic extracts of onion varieties and its representative phenolic compounds quercetin aglycone and quercetin 3-β-D-glucoside in the QS model bacteria Chromobacterium violaceum ATCC 12472, Pseudomonas aeruginosa PAO1, and Serratia marcescens MG1. Three phenolic extracts were obtained: red onion extract in methanol acidified with 2.5% acetic acid (RO-1), white onion extract in methanol (WO-1) and white onion extract in methanol ammonium (WO-2). Quercetin 4-O-glucoside and quercetin 3,4-O-diglucoside were identified as the predominant compounds in both onion varieties using HPLC-DAD and LC-ESI-MS/MS. However, quercetin aglycone, cyanidin 3-O-glucoside and quercetin glycoside were identified only in RO-1. The three extracts showed minimum inhibitory concentration (MIC) values equal to or above 125 µg/ml of dried extract. Violacein production was significantly reduced by RO-1 and quercetin aglycone, but not by quercetin 3-β-D-glucoside. Motility in P. aeruginosa PAO1 was inhibited by RO-1, while WO-2 inhibited S. marcescens MG1 motility only in high concentration. Quercetin aglycone and quercetin 3-β-D-glucoside were effective at inhibiting motility in P. aeruginosa PAO1 and S. marcescens MG1. Surprisingly, biofilm formation was not affected by any extracts or the quercetins tested at sub-MIC concentrations. In silico studies suggested a better interaction and placement of quercetin aglycone in the structures of the CviR protein of C. violaceum ATCC 12472 than the glycosylated compound which corroborates the better inhibitory effect of the former over violacein production. On the other hand, the two quercetins were well placed in the AHLs binding pockets of the LasR protein of P. aeruginosa PAO1. Overall onion extracts and quercetin presented antimicrobial activity, and interference on QS regulated production of violacein and swarming motility.

<p>Effect of Sub-Minimum Inhibitory Concentrations of Tyrosol and EDTA on Quorum Sensing and Virulence of <em>Pseudomonas aeruginosa</em></p>

“…61 A significant reduction in lecithinase production was observed only with 1/4x and 1/8x MIC of EDTA. These findings were similar to what was reported by previous studies on other compounds such as that conducted by Mattmann and Blackwell about furanone C-30, 62 Musthafa et al about phenylacetic acid, 63 Quecan et al about onion extract 58 and Ahmed et al about cinnamaldehyde and salicylic acid. 64 Motility is an important factor in both adhesion and biofilm formation.…”

“…24,26 Also, Aboelenin et al, 2017 reported a similar effect of sub-MICs of EDTA on the viability of E. coli. 51 Many studies reported that several antibacterial agents (tobramycin, 52 ciprofloxacin, 53 azithromycin, 54 ceftazidime, 48 aminoglycosides, tetracyclines 55 and piperacillin-tazobactam 56 ), natural plant-derived compounds as gall extract 2,57 and onion extract 58 and drugs such as aspirin 37 can decrease QS signals (HSL) in P. aeruginosa at sub-MICs without any bactericidal effect. Our study showed the same result whereas both tyrosol and EDTA at sub-MICs verified a significant reduction of C4-HSL and C12-HSL signal molecules production in P. aeruginosa PAO1.…”

Allium Flavonols: Health Benefits, Molecular Targets, and Bioavailability

“…They established that 4 -Qmg treatment prevented the production of virulence factors (violacein, elastase, and pyocyanin) and biofilm formation in the test pathogens by antagonizing the virulence factor regulator (Vfr) and QS signal receptor (LasR) [129]. Another recent study witnessed the anti-QS activity of quercetin aglycone and 3-Qmg from onion on C. violaceum, P. aeruginosa, and Serratia marcescens by inhibiting violacein production and swarming ability [130]. The above discussion imparts that the use of Allium-derived flavonols could be a sustainable solution to mitigate issues relating to the resistant microbial infections.…”

Effect of Daily Ingestion of Quercetin-Rich Onion Powder for 12 Weeks on Visceral Fat: A Randomised, Double-Blind, Placebo-Controlled, Parallel-Group Study

“…In a placebo-controlled double-blind parallel-group comparison study for subjects with body mass index (BMI) of ≥25 kg/m 2 , daily intake of tea containing 110 mg quercetin glycoside for 12 weeks significantly decreased visceral fat area (VFA) at weeks 8 and 12 after intake compared to that in the placebo food intake group [10]. The mechanism underlying suppression of fat accumulation by quercetin was indicated to involve suppression of the expression of peroxisome proliferator-activated receptor γ which is related to fat accumulation, and sterol regulatory element-binding protein 1 and fatty acid synthase which are related to fatty acid synthesis, and to increase the expression of cAMP which is related to lipolysis [11][12][13].Onion is the one of the most popular vegetables in the world, and a major source of quercetin (28.4-48.6 mg/100 g) [14]. In the current clinical trial, we used the two quercetin-rich onion cultivars 'Quergold' and 'Sarasara-gold' to adjust the amount of quercetin contained in the test food.…”

“…Onion is the one of the most popular vegetables in the world, and a major source of quercetin (28.4-48.6 mg/100 g) [14]. In the current clinical trial, we used the two quercetin-rich onion cultivars 'Quergold' and 'Sarasara-gold' to adjust the amount of quercetin contained in the test food.…”