This work was focused on in vitro evaluation of anti-biofilm and anti-quorum sensing effects of four selected flavonoid compounds /(+)-catechin, caffeic acid, quercetin and morin/ using the strain Pseudomonas aeruginosa PAO1. At a concentration of 0.5 MIC quercetin was the only compound found to potently reduce both P. aeruginosa biofilm formation (95%) and its twitching motility. The chemical scaffold of quercetin, a common dietary polyphenol, may actually inspire development of novel and more effective medicinal agents targeting P. aeruginosa, the bacterium well known for its resistance.
Methylglyoxal is a highly reactive α-oxoaldehyde with elevated production in hyperglycemia. It reacts with nucleophilic Lys and Arg side-chains and N-terminal amino groups causing protein modification. In the present study, the importance of the reaction of the Cys thiol group with methylglyoxal in protein modification, the competitiveness of this reaction with those of amino and guanidine groups, the time course of these reactions and their role and contribution to protein cross-linking were investigated. Human and bovine serum albumins were used as model systems. It was found that despite the very low levels of thiol groups on the surface of the examined protein molecules (approx. 80 times lower than those of amino and guanidino groups), a very high percentage of it reacts (25-85 %). The amount of reacted thiol groups and the rate of the reaction, the time for the reaction to reach equilibrium, the formation of a stable product and the contribution of thiol groups to protein cross-linking depend on the methylglyoxal concentration. The product formed in the reaction of thiol and an insufficient quantity of methylglyoxal (compared to the concentrations of the groups accessible for modification) participates to a significant extent (4 %) to protein cross-linking. Metformin applied in equimolar concentration with methylglyoxal prevents its reaction with amino and guanidino groups but, however, not with thiol groups.
This work extends in vitro screening of antimicrobial activity of the sesquiterpene hydroquinone avarol, a main secondary metabolite of the Mediterranean sponge species Dysidea avara. The antimicrobial activity was in part evaluated by microdilution method against selected bacterial and fungal strains. Additionally, the screening included evaluation of anti-quorum sensing (anti-QS) effects. At a different extent avarol was proven to be active against all the microorganisms tested (MIC 0.002-0.008 mg/mL and MBC 0.004-0.016 mg/mL; MIC 0.004-0.015 mg/mL and MFC 0.008-0.030 mg/mL; respectively). This marine natural product also showed moderate anti-QS effects, reducing Pseudomonas aeruginosa PAO1 biofilm formation (75%), its twitching and protrusions motilities as well as pyocianin production (39%). According to the best of our knowledge, this is the first report both on avarol anti Gram-negative bacterial activity and anti-QS effects.
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