Quercetin and Nano Quercetin: Cytotoxicity, Antileishmanial and Antimicrobial Activities against Resistance Strains

Background: Quercetin, a natural polyphenolic flavonoid compound, showed high anti-cancer, anti-bacterial, and anti-viral activities. Given the importance of microbial diseases, the lack of definitive treatment for many of them, and the emergence of drug resistance, it is essential to use various natural compounds to investigate their antimicrobial effects. We aimed to assess the anti-bacterial and anti-leishmanial activity in vitro and in vivo study. Methods: Anti-leishmanial effects of quercetin and nano-quercetin were evaluated on promastigote and amastigote stages in vitro. The minimal inhibitory concentrations (MICs) were determined by the broth dilution method using six species of clinical pathogenic bacteria strains, including Bacillus cereus, Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, Campylobacter jejuni, and Pseudomonas aeruginosa. Furthermore, the cytotoxicity effects of the drugs were evaluated using MTT assay. Results: All tested compounds presented anti-leishmanial and anti-microbial properties. Gram-negative bacteria were more resistant than gram-positive bacteria. Quercetin and nano-quercetin in concentrations of 200 and 400 µg/ml showed similar effectiveness on promastigote and amastigote of L. infantum in comparison to positive controls. In all experiments, nano-quercetin was more effective than quercetin. Moreover, no cytotoxicity activity was observed on Normal mouse fibroblast cell line (L929) in vitro. Conclusion: Nano-quercetin and even quercetin had excellent anti-microbial and anti-parasitic effects, and given that no toxicity was observed from these compounds even at higher concentrations, these compounds can be used as a suitable alternative for the treatment of parasitic and microbial diseases.