Melanization and morphological effects on antifungal susceptibility of Penicillium marneffei

Abstract

The biosynthesis of melanin has been linked with virulence in diverse pathogenic fungi. Penicillium marneffei, a dimorphic fungus, is capable of melanization in both mycelial and yeast phases, and the pigment may be produced during infection to protect the fungus from the host immune system. To investigate the impact of yeast morphological transformation on antifungal susceptibility, P. marneffei was cultured on various media including minimal medium, 1% tryptone, brain heart infusion broth, and malt extract broth by using the standardized susceptibility protocol (the M27-A protocol, RPMI medium) for yeasts. We also investigated whether P. marneffei melanization affected its susceptibility to antifungal drugs by adding L-DOPA into culture broths. There were no differences in the minimum inhibitory concentrations (MICs) of P. marneffei yeast cells previously grown in various culture broths with or without L-DOPA using the M27A protocol (into which no melanin substrate can be added due to a rapid color change of the RPMI medium to black) for testing amphotericin B, clotrimazole, fluconazole, itraconazole and ketoconazole. However, both melanized and non-melanized P. marneffei displayed increased resistance to antifungal drugs when L-DOPA was added into a selected assay medium, 0.17% yeast nitrogen base, 2% glucose, and 1.5% agar. Hence, active melanin formation appears to protect P. marneffei by enhancing its resistance to antifungal drugs.

Melanins Protect Sporothrix brasiliensis and Sporothrix schenckii from the Antifungal Effects of Terbinafine

“…We observed minor differences in susceptibility of melanized or non-melanized Sporothrix cells with the protocol for MIC determination described by the CLSI. This observation is consistent with that reported for other pathogenic fungi [ 22 , 33 , 34 ]. As previously described, the protection conferred by the S .…”

“…However, as detailed herein, production of eumelanin in RPMI-1640 medium could not be evaluated. As described by other authors [ 22 , 34 ], the addition of L-DOPA to this medium rapidly resulted in L-DOPA autopolymerization. Moreover, inoculating the Sporothrix strains of our study in this mixture resulted in an impairment of growth for all strains in the presence or absence of antifungal drugs.…”

“…One of the described functions for melanins produced by pathogenic fungi is the protection against antifungal drugs. This was observed for eumelanin producing fungi like Cryptococccus neoformans [ 22 , 31 ], Paracoccidioides brasiliensis [ 32 , 33 ], Histoplasma capsulatum [ 22 ], and Penicillium marneffei [ 34 ]. However, DHN-melanin producing strains of Fonsecaea monophora strains expressing melanin without precursors were not found to protect against antifungals [ 35 ] whereas DHN-melanin from Madurella mycetomatis and Aspergillus fumigatus were able to reduce the effects of ketoconazole and itraconazole [ 36 ].…”

Characterization of a novel yeast phase-specific antigen expressed during in vitro thermal phase transition of Talaromyces marneffei

“…The yeast antigen expressed www.nature.com/scientificreports/ from T. marneffei cells undergoing thermal phase transition was analyzed by indirect immunofluorescence and quantified by flow cytometry. In 1% proteose peptone, T. marneffei conidia readily converted to fission yeasts with a transverse septum, which is the T. marneffei morphotype seen in clinical specimens 15,16 (Fig. 6a1).…”

Human Colors—The Rainbow Garden of Pathology: What Gives Normal and Pathologic Tissues Their Color?

“…32,33 Interestingly, melanin pigments produced by fungi (dematiaceous fungi, Cryptococcus spp, Aspergillus spp, Candida spp, Penicillium spp, among others) have a role in the survival and virulence of these organisms by interfering with the host immune phagocytic mechanisms ( Figure 5, I). 5,34,35 Eumelanin is also the main component of the ink produced by coleoid cephalopods, that is squids (Teuthida), cuttlefish (Sepiida), and octopuses (Octopoda). Eumelanin is stored in an ink sac and released in several patterns (pseudomorphs, ink ropes, clouds, smokescreens, among others) and functions as a distractor to escape predation.…”