ABSTRACT
Microorganisms may enter buildings from outside but the most important sources are usually within the building. Organic dusts, rich in microorganisms, can originate from many different materials in buildings. They may come from wood-rotting and mould fungi in domestic buildings but from cereal grains and animal feeds in farm buildings. In buildings associated with other occupations, sources may include foods, fibre crops, timber and wood products, composts, biotechnological processes, cutting oils and even air-conditioning systems. Microorganisms may supply other components in organic dusts through their metabolites which may include endotoxins (lipopolysaccharides) from Gram-negative bacteria, enzymes from bacteria and fungi and mycotoxins and (1 → 3) β-D- glucans from fungi. These occur in a mixture with fragments of plants, starch grains, proteins and other components; mites, and their products, including fecal material; dander, urinary and serum proteins and fecal material from animals; soil; and, perhaps, pesticidal chemicals.
