Sundaram Challa, Shantveer G Uppin, Umabala Pamidi, Lakshmi Vemu
Department of Pathology, Nizam's Institute of Medical Sciences, Punjagutta, Hyderabad, Andhra Pradesh, India.
Indian J Pathol Microbiol. 2014 Apr-Jun;57(2):217-22. doi: 10.4103/0377-4929.134666.
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 difficult on morphology alone.
To study if melanin production by dematiaceous fungi can help differentiate them from other types of fungi.
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 filamentous fungi diagnosed on morphology alone with no culture confirmation.
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 filamentous fungi (9/15), Zygomycetes (4/5), and fungi with both hyphal and yeast morphology (4/4) showed positivity for melanin. The septate filamentous fungi negative for melanin were from biopsy samples of fungal sinusitis including both allergic and invasive fungal sinusitis and colonizing fungal balls.
Melanin is produced by both dematiaceous and non-dematiaceous fungi. Masson-Fontana stain cannot reliably differentiate dematiaceous fungi from other filamentous fungi like Aspergillus sp; however, absence of melanin in the hyphae may be used to rule out dematiaceous fungi from other filamentous fungi. In the differential diagnosis of yeast fungi, Cryptococcus sp can be differentiated from Candida sp by Masson-Fontana stain in tissue sections.
由于细胞壁中存在黑色素，暗色真菌在组织切片中呈棕色。当在常规苏木精和伊红染色中未见到棕色且无法进行培养时，仅靠形态学很难将暗色真菌与其他真菌区分开来。
研究暗色真菌产生的黑色素是否有助于将它们与其他类型的真菌区分开来。
对50份各种真菌感染的组织切片和13份来自不同真菌物种培养物的涂片进行马松·丰塔纳染色，以评估黑色素的产生情况。组织切片包括26份经培养证实的真菌活检标本以及24份仅根据形态学诊断而未经培养证实的丝状真菌活检标本。
所有经培养证实的暗色真菌和接合菌在切片和培养涂片上均显示强阳性。曲霉属显示出不同程度的阳性和强度。新型隐球菌在组织切片和培养涂片上显示强阳性。有隔丝状真菌（9/15）、接合菌（4/5）以及具有菌丝和酵母形态的真菌（4/4）的组织切片显示黑色素呈阳性。黑色素呈阴性的有隔丝状真菌来自真菌性鼻窦炎的活检样本，包括变应性和侵袭性真菌性鼻窦炎以及定植性真菌球。
暗色真菌和非暗色真菌均可产生黑色素。马松·丰塔纳染色不能可靠地将暗色真菌与曲霉属等其他丝状真菌区分开来；然而，菌丝中缺乏黑色素可用于排除暗色真菌与其他丝状真菌。在酵母样真菌的鉴别诊断中，在组织切片中可通过马松·丰塔纳染色将隐球菌属与念珠菌属区分开来。
