Resumo

The increased frequency of cross-resistance of microorganisms in clinical practices makes the search for new therapeutic strategies a reality today. Natural resources such as plants, microorganisms and invertebrates provide sources for the discovery of potential bioactive molecules. Flavonoids are a group of natural substances with a variable phenolic structure garnering considerable scientific and therapeutic interest. Catechin is a bioactive flavonoid with several biological properties, including antimicrobial effects. The aim of the current study was to evaluate the antifungal effect of catechin and their synergistic effect with fluconazole (FLC) in FLC-resistant strains of C. tropicalis via broth microdilution susceptibility test (CLSI document M27-A3), flow cytometry procedures and alkaline comet assay. Also, the cytotoxic effect of drugs against human leukocytes was assessed by MTT assay after 72 h exposure (37°C). Cultured C. tropicalis were exposed to catechin (0.125-128 µg/mL) or co-exposed with FLC (2 µg/mL) for 24 h (35°C). After treatments, catechin showed no activity (MIC50 > 128 µg/mL) against FLC-resistant strains of C. tropicalis or leukocytes (IC50 > 100 µg/mL). However, in co-treated (catechin plus FLC) strains, a synergistic effect of the drugs on FLC-resistant strains of C. tropicalis growth was observed, as demonstrated by reduction of MIC50 values (0.125 µg/mL) and by fractional inhibitory concentration index (FICI ≤ 0.5), but showed non-toxicity in leukocytes (IC50 > 100 µg/mL). Also, combined treatment promotes reactive oxygen species generation, indirect DNA damage and mitochondrial dysfunction triggering cell death by apoptosis highlighted by annexin V detection (phosphatidylserine externalization). In summary, combination of catechin with FLC demonstrated antifungal activity against strains of FLC-resistant C. tropicalis in vitro.