Abstract: Objective To seek a cost-effective method for isolation of dematiaceous fungi from soil. Methods Four concentrations of soil suspension samples were prepared by ten-fold serial dilution （1, 1 ∶ 10, 1 ∶ 100, 1 ∶ 1000）. Then, each concentration of sample was divided into two parts: one part supplemented with antibiotics, including chloramphenicol, cycloheximide, penicilin and streptomycin, and the other free of antibiotics. Three culture media were prepared: Sabouraud′s dextrose agar（SDA）, potato dextrose agar（PDA） and rose bengal medium （RBM）. Various concentrations （0, 100, 200, 300, 500 mg/L） of cycloheximide were added into each culture medium along with defined concentration of penicillin （1000 u/mL） and streptomycin （0.2 g/L）. In addition, chloramphenicol （50 mg/L） was added to PDA. The prepared soil samples were inoculated into these media by spread plate and pour plate, respectively. Results The total isolation rate of dematiaceous fungi was 70% （56/80） for PDA, 67.5% （54/80) for RBM and 3.75% （3/80） for SDA. PDA and RBM were more efficient than SDA （both P < 0.05）. Significant difference was observed in the isolation rate of dematiaceous fungi between the original and 1:100 diluted soil suspension samples in PDA （50% vs 85%, P < 0.05） and RBM （45% vs 85%, P < 0.05）. An increased isolation rate was achieved in PDA （87.50% vs 31.25%） and RBM （81.25% vs 37.5%） with cycloheximide at 200 mg/L compared with those free of cycloheximide. No difference was found in the isolation rate between antibiotic-supplemented and antibiotic-free soil samples. Although there was no difference in the total isolation rate between spead plate and pour plate, a higher isolation rate was observed by pour plate from antibiotic-free soil samples in PDA （80% vs 40%, P < 0.05） and RBM （80% vs 30%, P < 0.05） compared with spread plate. Conclusions The modified PDA and RBM are suitable for the isolation of dematiaceous fungi from soil with the optimal concentration of cycloheximide being 200 mg/L in the medium. Pour plate is more convenient and cost-effective than spread plate for the isolation of dematiaceous fungi from soil.

Key words: Soil, Dematiaceae fungi, Isolation