Urban and rural regions are affected by different microorganism loads depending on their structure and utilization. At 7 sampling sites in the metropolitan area of Graz, counts of airborne bacteria as well as yeasts and molds were conducted over a one-year period at two-week intervals. Bacteria and yeasts/molds counts in a village area to the South of Graz dominated by agriculture exceeded the corresponding counts in a suburban residential area fourfold (327 CFU/m3 air-bacteria) and twofold (185 CFU/m3 air-yeasts/molds) respectively. In the vicinity of a composting facility located in the same residential area, microorganism counts exceeded those of the neighboring "unaffected" area by 29% in the case of bacteria and by 54% in the case of yeasts/molds. At an industrial and business site with heavy traffic, the counts are twice that of the area affected by the composting facility (146 CFU/m3 for bacteria and 168 CFU/m3 for yeasts/molds). The proportion of Aspergillus fumigatus is highest in the village area with 23%, compared to 10% in the open land. 49% of the bacteria and 54% of the yeasts and molds can be shown on stages 4-6 of the Andersen-Volumetric-Sampler registering the respirable particle sizes.

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