RESUMEN
The use of the Sensititre YeastOne YO10 alamarBlue assay for the in vitro susceptibility testing of Madurella mycetomatis was evaluated in M. mycetomatis isolates with and without pyomelanin secretion. Pyomelanin secretion did not influence visual endpoint reading; however, it caused a shift in peak absorbance from 570 nm to 620 nm when read spectrophotometrically. Therefore, when choosing the method for endpoint reading, the presence of pyomelanin should be considered.
Asunto(s)
Madurella/metabolismo , Melaninas/metabolismo , Micetoma/metabolismo , Azoles/metabolismo , Madurella/genética , Melaninas/genéticaRESUMEN
One of the hallmarks of eumycetoma is the formation of fungal grains, which are secreted by multiple sinuses in infected tissues. Madurella mycetomatis grains are black. This black colour was shown to be due to the presence of melanin. Melanin can be produced through various biochemical pathways. It appeared that M. mycetomatis melanisation could be blocked by inhibitors of the pyo- and dihydroxynaphthalene (DHN)-melanin pathways but not by inhibitors of the dihydroxyphenylalanine (L-DOPA)-melanin pathway. Melanin isolated from M. mycetomatis cells provides in vitro protection against the killing effects of the oxidant permanganate and several antifungals. When melanin was added to the culture medium, MICs were found to be 16-fold elevated in the case of itraconazole and 32-fold for ketoconazole. MICs for amphotericin B, fluconazole and voriconazole were not affected. Since itraconazole and ketoconazole are the main antifungal agents used to treat mycetoma, the clinical relevance of the in vitro rise in MIC should be studied further.
Asunto(s)
Antifúngicos/farmacología , Itraconazol/farmacología , Cetoconazol/farmacología , Madurella/metabolismo , Melaninas/biosíntesis , Micetoma/tratamiento farmacológico , Micetoma/microbiología , Farmacorresistencia Fúngica Múltiple , Humanos , Madurella/aislamiento & purificación , Madurella/patogenicidad , Melaninas/antagonistas & inhibidores , Melaninas/metabolismo , Oxidantes/químicaRESUMEN
We have isolated and characterized a rice isoflavone reductase-like gene, OsIRL, whose expression is induced by a fungal elicitor. The OsIRL cDNA contains 1203 bp with an open reading frame of 942 nucleotides encoding 314 amino acids. The deduced amino acid sequence of OsIRL has a putative pyridine nucleotide binding domain and is 68% homologous with the maize isoflavone reductase-like gene. Southern blot analysis revealed that OsIRL belongs to a small multigene family. Expression of OsIRL was induced by treatment with a fungal elicitor and jasmonic acid as well as by inoculation with rice blast fungus. Cycloheximide (1 microM), strongly inhibited the induction of OsIRL by the fungal elicitor, indicating that new protein synthesis is required. The protein kinase inhibitor, staurosporine (1 microM), had little effect, but the phosphatase inhibitor, calyculin A (1 microM), strongly inhibited induction. Treatment with salicylic acid (SA, 5 mM) strongly inhibited expression of OsIRL in response to fungal elicitor and JA, while abscisic acid (ABA, 200 microM) also strongly antagonized OsIRL induction by JA, but had only a weak effect on induction by the fungal elicitor. These results suggest that the expression of OsIRL is positively regulated by phytohormones such as JA, and negatively by phytohormones such as SA, ABA.