Stryphnodendron adstringens and purified tannin on Pythium insidiosum: in vitro and in vivo studies.

BACKGROUND: Pythium insidiosum is the etiological agent of pythiosis, an emerging life-threatening infectious disease in tropical and subtropical regions. The pathogen is a fungus-like organism resistant to antifungal therapy, for this reason, most cases need extensive surgical debridments as treatment, but depending on the size and anatomical region of the lesion, such approach is unfeasible. We investigate the fungicidal effect and toxicity of crude bark extract of Stryphnodendron adstringens and commercially available tannin on Pythium insidiosum both in vitro and in vivo. METHODS: Standardized fragments of mycelia of fifteen isolates of P. insidiosum were tested with different concentrations of bark extract (10 to 30% v/v) and tannin (0.5, 1.0 and 1.5 mg/mL). For in vivo study, fifteen rabbits were experimentally infected with zoospores of P. insidiosum and treated by oral and intralesional applications of bark extract and tannin. Acute toxicity tests with both substances were also performed in rats. RESULTS: In vitro studies showed fungicidal effect for both substances at different concentrations and the SEM showed alteration on the cell wall surface of the pathogen. All infected rabbits developed a firm nodular mass that reached around 90 mm2 ninety days after inoculation, but neither the intralesional inoculation of tannin, nor the oral administration of crude extract and tannin were able to promote remission of the lesions. CONCLUSIONS: Lesions developed by rabbits presented an encapsulated abscess being quite different of naturally acquired pythiosis, which is characterized by ulcerated lesions. Since no toxicity was observed in rats or rabbits inoculated with these products, while in vitro experiments showed direct antifungal effect, therapeutic activity of S. adstringens and tannin should be clinically tested as an alternative for healing wounds in naturally acquired pythiosis.

Antifungal activity of Tagetes patula extracts on some phytopathogenic fungi: ultrastructural evidence on Pythium ultimum.

Methanol extract, obtained from Tagetes patula plant, was assayed against three phytopathogenic fungi: Botrytis cinerea, Fusarium moniliforme and Pythium ultimum. The antifungal activity was tested both in the dark and in the light, using two different lighting systems. The data showed that the extract proved to have a dose-dependent activity on all the fungi with a marked difference between treatments in the light than in the dark. Good growth inhibition was observed in fungi only when these were treated with the highest dose of the extract and irradiated, whereas the same dose gave only a modest inhibition when the experiment was conducted in the dark. At 5 and 10 microg/ml in the dark, growth increased. The results indicated that the presence of a luminous source enhances the antifungal activity, with small differences between UV-A and solar spectrum light. SEM and TEM observations on Pythium ultimum revealed that the Tagetes patula extract induced alterations on cell fungal membranes with a photoactivation mechanism possibly involving the production of free radicals and leading to a premature aging of the mycelium.