Manfred Gareis, D.V.M., Ph.D., Prof., Eckardt Johanning, MD., M.Sc. Ritchie Dietrich, Ph.D. Institute for Microbiology and Toxicology, e-mail: gareis.baff@t-online.de

Several hydrophil fungi produce very potent chemical metabolites (mycotoxins) that may pose a particular health risk in indoor settings. However, these properties have not been routinely assessed in similar field investigations, due to a lack of readily available screening test methods. A total of 166 moulded samples of building materials (gypsum boards, wallpaper, ceiling tiles, fiberglass and other insulating materials, carpets, dust and air filters) from 44 case investigations conducted during the time period from 1993 to 1998 in various areas of the United States were tested with the MTT-cytotoxicity screening assey for the presence of cytotoxic mycotoxins and compared with controls. A subset of samples was analysed by an enzyme-immune assay (EIA) for occurrence of macrocyclic trichothecenes produced by strains of Stachybotrys chartarum. In addition, presence of fungi were examined by culture methods and scanning electron microscopy. Different levels of cytotoxicity were detected in particular of field samples of gypsum board or wall paper visibly contaminated with fungal growth. Samples with highly cytotoxic effects reacted positive in the MTT-bioassay at concentrations of less than 5 mg of sample aliquot per ml of cell culture medium and indicated the presence of cytotoxic contaminants. Twenty-three field samples (52%) of all case investigations were positive for cytotoxicity compared with controls. Most frequently detected fungi in toxic samples were Stachybotrys chartarum (85%), Trichoderma sp. (31%) and Chaetomium sp. (38%) compared to non-cytotoxic samples with a proportion of 38%, 10% and 5%, respectively. These results indicated the presence of non-toxigenic strains or alternatively the non-production of cytotoxic mycotoxins by toxigenic strains on these particular samples. The level of toxicity obtained by the MTT-bioassay highly correlated with the amount of macrocyclic trichothecenes detected by use of the EIA in the samples contaminated with or without Stachybotrys chartarum. Toxicity detected in samples not contaminated with Stachybotrys chartarum indicates the presence of cytotoxic mycotoxins produced by other fungi. In conclusion, the results support the usefulness of the MTT cytotoxicity assay as an important diagnostic tool for the assessment of potential mycotoxin exposure inside buildings with fungal contamination.