Characterization of three native Streptomyces isolates that inhibit the growth of fluconazole-resistant Candida spp strains.

Most fungal infections are caused by species of the Candida genus, particularly C. albicans. The increasing number of strains developing resistance to antifungals, resulting in treatment failures, underscores the urgency of finding new antifungal agents. Since many bacteria of the genus Streptomyces produce molecules that inhibit fungal growth, this work aimed to evaluate the antifungal activity of three native isolates obtained from a rhizosphere and an artisanal composting system. Based on 16S RNA gene sequences, as well as biochemical and morphological traits, we identified S. globisporus, S. bacillaris, and S. cavourensis as the species most closely related to the S1H, S40, and S41 isolates, respectively. These species have been reported to produce antifungal compounds. Theinhibition of Candida by antagonistic activity increased with longer Streptomyces incubation times, with no differences observed between Candida species. Few studies have simultaneously evaluated the inhibitory activity of Streptomyces isolates against different Candida strains. In this study, the isolates inhibited the growth of C. albicans, C. krusei, C. guilliermondii, C. glabrata, and C. lusitaniae, including strains resistant to fluconazole.