Background: Biological growth on building materials is directly linked to exposure of these materials to moisture. Growth of microbes also depends on the chemical composition of the material. Therefore selection of materials that will prevent the onset of the microbial growth in the presence of moisture-damage is important. Methods: In the present study, we evaluated the growth of three different fungi - Aspergillus versicolor, Cladosporium cladosporioides and Penicillium brevicompactum - on five building materials: green (acoustic board 1 and haltex) and non-green (acoustic board 2 and gypsum board). Wood was included as a conventional material. Different surfaces of the materials were inoculated with fungi, in the absence and presence of house dust. The water holding capacity (WHC) of materials was determined by immersing building material samples in water until they were fully saturated. WHC was expressed as the mass ratio of water to dry materials. Microbial growth was assessed at four different time points (day 0 and weeks 1, 2 and 4) by cultivation and determining fungal biomass using the NAHA enzyme assay. Results: The results showed that NAHA activity and culturable count correlated well for A. versicolor, (R2=0.61) C. cladosporioides (R2=0.57), but not for P. brevicompactum (R2=0.18). The presence of dust serving as external source of nutrient promoted growth of all the fungal species on gypsum board and wood. Also, wood and gypsum board in the absence of dust supported significant growth. The top surfaces of the two acoustic boards had little or no activity while the sides of the same materials had significant activity. Even though haltex had the highest WHC, it did not support significant microbial growth compared to gypsum board and wood, which had lower WHCs. Conclusions: The results suggest that the growth of microbes on a material surface depends on the availability of organic matter on the material surface rather than the classification of the material as green or non green.
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