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Identification of Stachybotrys chartarum Utilizing Various Media and Two Temperature Settings

Richard A. Billups, Kristen S. Tilton, Ph.D. and Paul S. Warden Analytical Services, Inc.

Identification of Stachybotrys chartarum can be difficult due to its slow growth, lack of expression of characteristic morphological features and competition from other more aggressive fungi. Cellulose Agar has been recommended as the choice media for recovering S. chartarum, however our research lends support for using different media for recovery and identification of S. chartarum. Two environmental isolates of S. chartarum (ATCC 9182 and 34915) were analyzed on six agars at 22°C and 35°C. The agars utilized were Cellulose Agar (CA), Cellulose Agar with 2% NaNO ₃ (CA2%), Potato Dextrose Agar (PDA), Cornmeal Agar (CMA), Cornmeal Agar with 2% NaNO ₃ (CMA2%), and Malt Extract Agar (MEA). Plates were examined daily for two weeks. Only the PDA plates at both temperatures exhibited deep black S. chartarum colonies with deep brown reverse colors. Colonies on Cellulose Agars and MEA demonstrated light brown coloration and reverse coloration varied from no coloration to very light brown coloration. The Cornmeal Agars produced colonies with diffuse black coloration and very minor reverse coloration. Microscopic examination revealed that dark brown/black spinose spores and verrucose dematiaceous hyphae typical of S. chartarum were best demonstrated on PDA and the CMAs. These results were apparent in both media even at early stages of growth and at both 22°C and 35°C. We support the use of PDA at 35°C to reduce competition from non-thermotolerant fungi. Under these experimental conditions, color development was substantially faster on PDA than any of the other six media examined, allowing easier recognition of macroscopic morphology and enumeration of S. chartarum.

Presented at the First NSF International Conference on Indoor Air Health: Impact, Issues and Solutions, May 3-5,