New insights into the antibacterial mode of action of quercetin against uropathogen Serratia marcescens in-vivo and in-vitro

Antibacterial and antibiofilm efficacy of quercetin against Pseudomonas aeruginosa and methicillin resistant Staphylococcus aureus associated with ICU infections

Infections caused by multidrug-resistant pathogens, particularly in ICU settings, pose significant health risks globally. Pseudomonas aeruginosa (PA) and methicillin-resistant Staphylococcus aureus (MRSA) are prominent nosocomial pathogens among the ESKAPE group, known for their resistance mechanisms such as biofilm formation and quorum sensing. Quercetin, a flavonoid found in fruits and vegetables, exhibits diverse pharmacological properties, including antimicrobial activity. This study evaluated quercetin's efficacy against PA and MRSA through in vitro and in vivo experiments. Minimum Inhibitory Concentration (MIC) assays showed MIC values of 158 µg mL-1 for PA and 176 µg mL-1 for MRSA. Quercetin inhibited PA's swarming motility at concentrations as low as 39.5 µg mL-1 and reduced MRSA viability in serum by up to 79%. Quercetin treatment significantly reduced biofilm formation by both pathogens, with Pseudomonas aeruginosa showing biomass reductions of 23% at 1/4 MIC (39.5 µg mL-1) and 48% at 1/2 MIC, while methicillin-resistant Staphylococcus aureus exhibited reductions of 27% at 1/4 MIC and 53% at 1/2 MIC compared to the control. High-content fluorescence imaging demonstrated quercetin's ability to disrupt biofilm structure and viability. Moreover, quercetin suppressed EPS production and protease activity in both PA and MRSA, alongside downregulating virulence-related genes involved in quorum sensing and toxin production. In vivo studies using Caenorhabditis elegans confirmed quercetin's ability to reduce bacterial adherence and colonization. These findings underscore quercetin's potential as a therapeutic agent against multidrug-resistant pathogens in ICU settings, warranting further exploration for clinical applications.

In vitro antibacterial activity of photoactivated flavonoid glycosides against Acinetobacter baumannii

Acinetobacter baumannii's extensive antibiotic resistance makes its infections difficult to treat, so effective strategies to fight this bacterium are urgently needed. This study aims to evaluate the effectiveness of antimicrobial photodynamic therapy (aPDT) mediated by Rutin-Gal(III) complex and Quercetin against A. baumannii. Absorbance spectra, fluorescence spectra, and minimum inhibitory concentration (MIC) of Rutin-Gal(III) complex and Quercetin were determined. The intracellular reactive oxygen species (ROS), extracellular polymeric substances (EPS), cell membrane permeability, expression of ompA and blaOXA-23, anti-biofilm activity, and anti-metabolic activity of Rutin-Gal(III) complex- and Quercetin-mediated aPDT were measured. Rutin-Gal(III) complex and Quercetin revealed absorption peaks in the visible spectra. Quercetin and Rutin-Gal(III) complex displayed fluorescence peaks at 524 nm and 540 nm, respectively. MIC values for the Rutin-Gal(III) complex and Quercetin were 64 µg/mL and 256 µg/mL, respectively. Quercetin- and Rutin-Gal(III) complex-mediated aPDT significantly reduced the colony forming units/mL (58.4% and 67.5%), EPS synthesis (47.4% and 56.5%), metabolic activity (30.5% and 36.3%), ompA (5.5- and 10.5-fold), and blaOXA-23 (4.1-fold and 7.8-fold) genes expression (respectively; all P < 0.05). Quercetin- and Rutin-Gal(III) complex-mediated aPDT enhanced notable biofilm degradation (36.2% and 40.6%), ROS production (2.55- and 2.90-folds), and membrane permeability (10.8- and 9.6-folds) (respectively; all P < 0.05). The findings indicate that Rutin-Gal(III) complex- and Quercetin-mediated aPDT exhibits antibacterial properties and could serve as a valuable adjunctive strategy to conventional antibiotic treatments for A. baumannii infections. One limitation of this study is that it was conducted solely on the standard strain; testing on clinical isolates would allow for more reliable interpretation of the results.

Synergistic defense: Quercetin and chondroitin sulfate combat bacterial trigger of rheumatoid arthritis, Proteus mirabilis through in-vitro and in-vivo mechanisms

Rheumatoid arthritis, a chronic autoimmune disorder characterized by joint inflammation, is thought to be exacerbated by bacterial infections, notably Proteus mirabilis. This study explores the combined effects of quercetin, a potent antioxidant and anti-inflammatory flavonoid, and chondroitin sulfate, known for its cartilage-protective properties, as a potential therapeutic approach. Molecular docking analyses revealed favourable interactions between these compounds and key pro-inflammatory cytokines IL-6 and TNF-α, suggesting their potential to disrupt inflammation-related signaling pathways. In vitro assays demonstrated that the quercetin- chondroitin sulfate combination (1:1 ratio) significantly inhibited oxidative stress and hemolysis, highlighting its enhanced anti-inflammatory and membrane-protective effects. The free radical scavenging assays further confirmed the antioxidant potential of this combination, which demonstrated strong radical scavenging activity. Antimicrobial assays showed notable antibacterial effects, with an increased inhibition zone against P. mirabilis when quercetin and chondroitin sulfate were combined, suggesting a synergistic antimicrobial action. In vivo, zebrafish subjected to bacterial stress showed improved survival rates with the quercetin and chondroitin sulfate combination treatment, along with enhanced mineralization and significant modulation of alkaline phosphatase (ALP) and tartrate-resistant acid phosphatase (TRAP) activities, indicating its protective role in maintaining joint health. Furthermore, gene expression analysis revealed a substantial reduction in pro-inflammatory markers, including TNF-α and IL-6, demonstrating the quercetin and chondroitin sulfate combination's ability to mitigate inflammation. Together, these findings suggest that the quercetin and chondroitin sulfate combination hold significant therapeutic potential in reducing oxidative stress, inflammation, and microbial-induced RA exacerbations.

Effect of amikacin-humic acid combination on Acinetobacter baumannii biofilm: an in vitro and in silico study

Aim: Acinetobacter baumannii (AB) is a clinically important bacterial pathogen responsible for nosocomial infections. The biofilm-forming capability of these pathogens reduces the antibiotic penetration and its efficacy, thereby complicating the treatment. The current work aims to isolate the most potent biofilm-forming Acinetobacter species from clinical isolates of the patient samples and to evaluate the efficacy of the amikacin-humic acid combination against it.Methods: The combination effect of Amikacin-Humic (AMK-HUM) acid against the highest biofilm-producing A. baumannii SLMK001 was studied via in-vitro (microscopic analysis) and in-silico (Network Pharmacology) analysis.Results: The amikacin-humic acid combination significantly inhibited both the biofilm formation and cell viability of A. baumannii SLMK001. The images observed via Scanning Electron Microscope (SEM) showed a significant decrease in the biofilm matrix. Confocal Laser Scanning Microscope (CLSM) confirmed a reduction of the Z value of its three-dimensional structure. Further, the Network Pharmacology approach supported these experimental findings by identifying the key targets of the amikacin-humic acid combination against the biofilm pathways of A. baumannii.Conclusion: The in-vitro results aligned with the in-silico findings, indicating that the AMK-HUM combination is a promising treatment that significantly activates the key proteins against A. baumannii biofilm formation and pathogenesis.

Quercetin's antibiofilm effectiveness against drug resistant Staphylococcus aureus and its validation by in silico modeling

Staphylococcus aureus is typically treated with antibiotics, however, due to its widespread and unselective usage, resistant strains of S. aureus have increased to a great extent. Treatment failure and recurring staphylococcal infections are also brought on by biofilm development, which boosts an organism's ability to withstand antibiotics and is thought to be a virulence factor in patients. The present study investigates the antibiofilm activity of naturally available polyphenol Quercetin against drug-resistant S. aureus. Micro dilution plating and tube adhesion methods were performed to evaluate the antibiofilm activity of quercetin against S. aureus. Quercetin treatment resulted in remarkably reduction of biofilm in S. aureus cells. Further we performed a study to investigate binding efficacies of quercetin with genes icaB and icaC from ica locus involved in biofilm formation. 3D structure of icaB, icaC and quercetin were retrieved from Protein data bank and PubChem chemical compound database, respectively. All computational simulation were carried out using AutoDock Vina and AutoDockTools (ADT) v 1.5.4. In silico study demonstrated a strong complex formation, large binding constants (Kb) and low free binding energy (ΔG) between quercetin and icaB (Kb = 1.63 × 10-5, ΔG = -7.2 k cal/mol) and icaC (Kb = 1.98 × 10-6, ΔG = -8.7 kcal/mol). This in silico analysis indicates that quercetin is capable of targeting icaB and icaC proteins which are essential for biofilm formation in S. aureus. Our study highlighted the antibiofilm activity of quercetin against drug resistant pathogen S.aureus.

Naturally occurring quercetin and myricetin as potent inhibitors for human ectonucleotide pyrophosphatase/phosphodiesterase 1

Ecto-nucleotide pyrophosphatases/phosphodiesterases 1 (ENPP1) is a key enzyme in purinergic signaling pathways responsible for cell-to-cell communications and regulation of several fundamental pathophysiological processes. In this study, Kyoto Green, a rapid chemical sensor of pyrophosphate, was employed to screen for effective ENPP1 inhibitors among five representative flavonoids (quercetin, myricetin, morin, kaempferol, and quercetin-3-glucoside), five nucleosides (adenosine, guanosine, inosine, uridine, and cytidine), and five deoxynucleosides (2'- and 3'-deoxyadenosine, 2'-deoxyguanosine, 2'-deoxyinosine, and 2'-deoxyuridine). Conventional colorimetric, fluorescence, and bioluminescence assays revealed that ENPP1 was effectively inhibited by quercetin (Ki ~ 4 nM) and myricetin (Ki ~ 32 nM) when ATP was used as a substrate at pH 7.4. In silico analysis indicated that the presence of a chromone scaffold, particularly one containing a hydroxyl group at the 3' position on the B ring, may promote binding to the active site pocket of ENPP1 and enhance inhibition. This study demonstrated that the naturally derived quercetin and myricetin could effectively inhibit ENPP1 enzymatic activity and may offer health benefits in arthritis management.