Multidrug-resistant bacterial infections are one of the most serious public health threats in the world, which bring an urgent need to discover novel antibiotics with enhanced broad-spectrum antibacterial activity . Curcumin , as a widely used natural product , has good anti-inflammatory and antioxidant properties; while, the bioavailability, bioactivity and antibacterial activity design are limited by its poor water-solubility. Here, to improve the bioactivity of curcumin, we show the fabrication of highly water-solvable carbon dots (CDs) by hydrothermal method from citric acid and curcumin. The CDs possess excellent broad-spectrum antibacterial activity and antibiofilm activity because they can do damage to the bacterial walls when they get into the bacteria. The bactericidal efficiency of CDs (375 μg/mL) achieves up to 100 % for Gram-negative bacteria ( Escherichia coli and Pseudomonas aeruginosa ). Additionally, for Gram-positive bacteria ( Staphylococcus aureus and Bacillus subtilis ), the bactericidal efficiency reaches 80 %. In addition, these CDs also can completely inhibit the formation of biofilm for the Gram-negative bacteria and the Gram-positive bacteria. This work has a significant meaning in studying new antibacterial nanomaterials derived from natural product and the treatment of infections.
Objective The aim of this study was to investigate the antibiofilm activity of coumarin against Candida albicans . Methods The efficacy of coumarin against biofilm formation and the mature biofilm of C. albicans was quantified by crystal violet (CV) staining and the 2,3-bis (2-methoxy-4-nitro-5-sulfophenyl)-5-[(phenylamino)carbonyl]-2H-tetrazolium hydroxide (XTT) reduction assay. The effect of coumarin on C. albicans adhesion was assessed on polystyrene plates and by using the cell surface hydrophobicity (CSH) assay. The morphological transition of C. albicans was conducted in two types of hyphae-inducing media at 37 °C. The expression of hypha/biofilm-related genes was evaluated using qRT-PCR analysis. A rescue experiment involving addition of exogenous cyclic adenosine monophosphate (cAMP) was performed to investigate the involvement of cAMP in the yeast-to-hyphae transition. A C. albicans -infected Caenorhabditis elegans model was used to test the anti-virulence efficacy of coumarin. Results Treatment with coumarin strongly affected the capacity of C. albicans to form biofilm and significantly impaired the preformed mature biofilm. The addition of coumarin notably inhibited C. albicans adhesion, CSH, and filamentation . The expression of some adhesion- and hypha-related genes, including HWP1 , HYR1 , ECE1 , and ALS3 , was remarkably down-regulated upon exposure to coumarin. Supplementation with cAMP partly rescued the coumarin-induced defects in hyphal development. Finally, coumarin prolonged survival in C. albicans -infected nematodes. Conclusion Coumarin inhibited C. albicans biofilm, which was associated with attenuated adhesion and hyphal growth.
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