Diagnostic utility of melanin production by fungi: Study on tissue sections and culture smears with Masson-Fontana stain.
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Date
2014-04
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Abstract
Background: Dematiaceous fungi appear brown in tissue section due to
melanin in their cell walls. When the brown color is not seen on routine H
and E and culture is not available, differentiation of dematiaceous fungi from
other fungi is diffi cult on morphology alone. Aims and Objective: To study if
melanin production by dematiaceous fungi can help differentiate them from
other types of fungi. Materials and Methods: Fifty tissue sections of various
fungal infections and 13 smears from cultures of different species of fungi were
stained with Masson Fontana stain to assess melanin production. The tissue
sections included biopsies from 26 culture-proven fungi and 24 biopsies of
fi lamentous fungi diagnosed on morphology alone with no culture confi rmation.
Results: All culture-proven dematiaceous fungi and Zygomycetes showed
strong positivity in sections and culture smears. Aspergillus sp showed variable
positivity and intensity. Cryptococcus neoformans showed strong positivity in
tissue sections and culture smears. Tissue sections of septate fi lamentous fungi
(9/15), Zygomycetes (4/5), and fungi with both hyphal and yeast morphology
(4/4) showed positivity for melanin. The septate fi lamentous fungi negative for
melanin were from biopsy samples of fungal sinusitis including both allergic and
invasive fungal sinusitis and colonizing fungal balls. Conclusion: Melanin is
produced by both dematiaceous and non-dematiaceous fungi. Masson-Fontana
stain cannot reliably differentiate dematiaceous fungi from other fi lamentous fungi
like Aspergillus sp; however, absence of melanin in the hyphae may be used
to rule out dematiaceous fungi from other fi lamentous fungi. In the differential
diagnosis of yeast fungi, Cryptococcus sp can be differentiated from Candida
sp by Masson-Fontana stain in tissue sections.
Description
Keywords
Dematiaceous, fungi, non-dematiaceous, Masson-Fontana, melanin
Citation
Sundaram Challa, Shantveer G Uppin, Umabala Pamidi, Lakshmi Vemu. Diagnostic utility of melanin production by fungi: Study on tissue sections and culture smears with Masson-Fontana stain. Indian Journal of Pathology & Microbiology. 2014 Apr-Jun 57 (2): 217-222.