Microbial growth on plasterboard and spore-induced cytotoxicity and inflammatory responses in vitro

Moisture damage and microbial growth in buildings have been associated with health effects among the occupants including various respiratory symptoms and asthma. However, the causative agents and the underlying mechanisms that are responsible for the adverse health effects associated with exposure in buildings are not clear. The basic phenomenon of microbial growth on building materials must be better understood. One possibility is that the growth conditions of microbes on wetted building materials are different from the natural environment, and this may encourage the microbes to produce biologically active compounds. In this thesis the growth of four microbes Stachybotrys chartarum, Aspergillus versicolor, Penicillium spinulosum, and Streptomyces californicus isolated from moisture damaged buildings was studied on six commercially available plasterboards and separately on the liners and cores of those boards. The biological activity of the spores was assessed as the ability of the spores to induce cytotoxicity and the production of pro-inflammatory cytokines and nitric oxide in mouse macrophages. Moreover, the effects of plasterboard composition and the use of a biocide on microbial growth and subsequent biological activity of spores were tested. There were considerable differences between commercially available plasterboards in their ability to support microbial growth with subsequent production of biologically active compounds capable of inducing inflammatory and toxic reactions in mammalian cells. These microbiological and immunological reactions depended also on the microbial species. Stachybotrys chartarum grew consistently faster than the other studied microbes whereas the spores of Streptomyces californicus were the most potent inducers of inflammatory responses. In some cases, microbial growth and biological activity of spores were more abundant on cores than on liners. The studies of plasterboard compositions revealed that growth of both S. chartarum and Str. californicus decreased compared to reference board in those cases where (a) the liner was treated with a biocide, (b) starch was removed from the plasterboard, or (c) desulforisation gypsum (DSG) was used in the core. Addition of the biocide into the core inhibited the growth of Str. californicus almost completely but did not reduce the growth of S. chartarum. In fact the spores of S. chartarum collected from that board evoked the highest detected cytotoxicity. Removal of starch reduced the bioactivity of Str. californicus spores but it did not affect that of S. chartarum spores. Altogether, these results suggest that microbial growth on plasterboard and subsequent biological activity of spores is not only due to the paper liner of plasterboard, but the core material also has a crucial role. The microbial growth and biological activity of spores can be affected by minor changes to the composition of core or liners but it cannot be totally prevented without resorting to the use of biocides. However, the use of biocides has to be carefully evaluated since incomplete prevention of microbial growth by biocides may even increase the harmfulness of the microbial spores.