EFFECT OF TANNINS FROM STRYPHNODENDRON ADSTRINGENS ON GROWTH AND MORPHOLOGY OF CRYPTOCOCCUS NEOFORMANS

Kelly Ishida (UFRJ); Sonia Rozental (UFRJ); João Carlos Palazzo de Mello (UEM); Celso Vataru Nakamura (UEM)

Stryphnodendron adstringens (Mart.) Coville, Leguminosae, also known in Brazil as barbatimão, is rich in tannins and many flavan-3-ols such as proanthocyanidins (prodelfinidins and prorobinetinidins). Previous studies have demonstrated several pharmacological properties of tannins from barbatimão, including anti-candidal activity. In this study, we evaluated the anti-cryptococcal activity of proanthocyanidins polymeric tannins extracted from barbatimão (subfraction F2.4) against three Cryptococcus neoformans strains: T₁-444, ATCC 28957 (both with capsule) and Cap 67 (acapsular mutant). All strains were susceptible to fluconazole, itraconazole, and amphotericin B.

The minimum inhibitory concentration (MIC) were determined using broth microdilution technique and then aliquots of yeasts pre-treated with subfraction F2.4 were cultivated on Sabouraud dextrose medium free-drug for obtaining the minimum fungicidal concentration (MFC). Although susceptibility assays revealed MIC values quite similar (between 2.5-5 µg/ml), analysis of MFC values revealed that the acapsular mutant Cap 67 was more susceptible for killing by the subfraction F2.4 (MFC = 20 µg/ml) than the others two capsular strains (T₁-444 and ATCC 28957) (MFC > 160 µg/ml). In order to examine the effect of subfraction F2.4 on the morphology C. neoformans, yeasts were cultivated or not in the presence of the subfraction F.24 and examined by light microscopy. Interestingly, the treatment of capsular strains with 1 and 2.5 µg/ml of subfraction F2.4 lead to a significant reduction on capsule size and decrease of cell size when compared with the non-treated yeasts (p<0.01). Treatment of these yeasts with subfraction F2.4 also leads to several morphological alterations such as: (i) the non separation of young bud cell; (ii) elongation of the young buds; (iii) appearance of smaller yeasts. Cap 67 strain present similar alterations in yeast morphology from those observed in the capsular strains but did not show any reduction of the cell size after the treatment.

In conclusion, tannins from S. adstringens interfere on growth, capsular and cell size of C. neoformans and may be considered as a putative candidate for development of a new antifungal agent.