Distribution and in Vitro Pathogenic Profile of Melanized Fungi Isolated from Rotten Wood and Soil

Melanized fungi have captivated most researchers due to emerging subcutaneous infections globally. This study was conducted to investigate the distribution (prevalence), identification, and in vitro pathogenic potential of melanized fungi isolated from loamy soil, clay soil, and rotten wood at Amorka, Eziama, and Ndikeokwu communities, Anambra State, Nigeria. Forty five (45) samples comprising loamy soil (15), clay soil (15), and rotten wood (15) were collected and cultured on Sabouraud dextrose agar supplemented with chloramphenicol (0.05%). The fungal isolates were characterized based on their cultural and microscopic features. An in vitro pathogenic potential of the fungal isolates was evaluated using haemolysis on blood agar, thermotolerance potential, and Congo red test. Three different isolates of melanized fungi with diverse occurrences were isolated and identified as Exophiala jeanselmei 18(23.1%), Cladosporium species 32(41.0%), and Alternaria alternata 28(35.9%). Rotten wood harboured the highest proportion of the isolates (48.7%), followed by loamy soil (32.1%) and clay soil (19.2%). Thermotolerance test revealed strong growth of E. jeanselmei at 37 °C, moderate growth of A. alternata at 37 °C, and poor growth of Cladosporium. Congo red test at 100 μg/ml revealed resistance in E. jeanselmei (78-85%), moderate resistance in A. alternata, and sensitivity in Cladosporium (25-35%). Complete haemolysis on 5% sheep red blood cells was observed in E. jeanselmei, partial haemolysis was observed in A. alternata while gamma (zero) haemolysis was observed in Cladosporium species. The study has established that rotten wood is a reservoir of potentially pathogenic melanized fungi, with Exophiala jeanselmei exhibiting the highest virulence potential. However, further study is highly essential to evaluate an in vivo pathogenic potential of the fungal isolates, especially E. jeanselmei and molecular characterization.