A study of fungal flora of house dust and its importance to public health.

TOYAZAKI Noritsuna

doi:10.2520/myco.52.45

1. A total of 19,716 strains of microfungi were isolated and identified from 533 samples of house dust collected in nine homes. The dust samples were collected monthly for one year using the home-owner′s vacuum cleaner fitted with a new collection bag. Molds belonging to the Deuteromycota were the most frequent group detected in dust (59.4% of the total fungi). Penicillium (1.2 × 10⁴ CFU/g), Phoma (7.7 × 10³ CFU/g) and Cladosporium (7.0 × 10³ CFU/g ) were frequently isolated and revealed important concentrations in the dust samples. Fungal colony counts in the house dust were higher in spring and midsummer, the peak periods being March-April and August. 2. Fungal propagules of 98 house dust samples from asthmatic patients, dwellings were compared by three isolation methods: dilution plate,ethanol pretretment and Warcup & Bakers ′ methods. Hydrophilic and mesophilic Deuteromycota in which growth can develop only at water activity values (Aw) greater than 0.80 were detected on PDA by dilution plating,while the microfungi developed on DG-18 plates by the same method were xerophilic and xerotolerant. The latter were Eurotium spp., Aspergillus restrictus and Wallemia sebi. After the ethanol treatment, Chaetomium spp. and Nigrospora oryzae were predominantly encountered in the same samples. The application of Warcup & Bakers′ method (treatment with ethanol and heating at 60°C) resulted the isolation of heatresistant Ascomycota such as species of Talaromyces, Eurotium, Nigrospora and Eupenicillium. 3. To study moisture contents of house dust and fungal growth relations,laboratory experiments under fiver levels of water activity (Aw 0.901, 0.807, 0.752, 0.708 and 0.577) at steady-state temperture of 25°C. In the total counts on PDA plate,there was mostly a decrease in the numbers of viable fungi in the Aw 0.807, 0.752, 0.708 and 0.577 chambers. However, at Aw 0.901, the number of fungi increased rapidly until three months. In the total counts on DG-18 plate, the experiments at Aw 0.807 to 0.752 show a remarkable growth of xerophilic fungi such as Aspergillus restrictus, Eurotium spp. and Wallemia sebi. In the experiments,high moisture count (Aw 0.901) was shown to be an important factor for the growth of Aspergillus versicolor. On the other hand, the optimal growth of Aspergillus restrictus had been observed on the house dust samples in Aw 0.752 or even 0.708 chambers.

A study of fungal flora of house dust and its importance to public health.

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