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The aim of our study was to screen Moroccan actinomycete isolates able to produce nonpolyenic antifungal metabolites in order to contribute to limiting the problem of fungal infections emergence in particular mycotic diseases and to discover known antifungal families, especially nonpolyenic drugs. 480 isolates were tested against 5clinically pathogenic Candida species. Several methods have been used to study the polyenic or non-polyenic nature of the antifungal molecules produced by Actinobacteria (i) The study of the antibacterial activity (the bacterial plasma membrane is devoid of sterols); (ii) The screening of the antimicrobial activity of resistant strains to polyenic antifungals essentially Candida tropicalis R2 and Pythium irregular; (iii) The inhibition of antifungal activity by exogenous ergosterol addition in the culture medium and (iv) The UV-Visible light spectrophotometric analysis of the crude extracts of the actinomycete isolates. Among all isolate tested, only 60 (29 %) showed an antifungal activity against all test microorganisms used. Six active isolates meet all the selection criteria and produced nonpolyenic antifungal metabolites. The taxonomic study of the promising isolate Z26, using morphological, physiological and molecular characters, showed that it has 99,43% of similarity with Streptomyces phytohabitans but there were some differences in morphological characteristics. In addition, the chemical study, using chromatographic and spectroscopic techniques, of the bioactive substances produced in the Z26 isolate fermentation broth in NL300 culture medium allowed the determination of two macrolide derivatives with chemical structures C 62 H 100 O 24 (m/z 1251.6504 [M+Na] +) and C 68 H 110 O 26 (m/z 1365.7174 [M+Na] +). NMR experiments revealed that the active compounds were Novonestmycin A and B. The Novonestmycins A and B are for the first time produced by an actinomycete strain purely isolated from the Moroccan ecosystems.

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