Background Concentrations of Cultivable, Mesophilic Bacteria and Dust Particles in the Air in Urban, Rural and Mountain Regions.

Particulate air components can be of anthropogenic or natural origin. It is assumed that in different geographical areas varying concentrations of mesophilic bacteria are present in the ambient air. The aim of this study was to determine the background concentrations of airborne culturable mesophilic bacteria and particulate matter in the ambient air. Furthermore, the association between their concentrations and some environmental factors was analysed. In the period from July to October 2019, concentrations of mesophilic bacteria and dust particles were measured in urban, rural and mountain areas using the single-stage air sampler and the particle counter. The concentrations of bacteria and dust particles in the air were counted as number of Colony Forming Units per cubic metre (CFU/m3) and particles per cubic metre (pa/m3). Staphylococcus sp. were identified. The median values of the cultivated mesophilic bacteria at 30 °C and 37 °C were 7.1 × 102 CFU/m3 and 2.3 × 101 CFU/m3 in mountain regions, 1.3 × 102 CFU/m3 and 6.9 × 101 CFU/m3 in rural regions and 2.1 × 102 CFU/m3 and 6.5 × 101 CFU/m3 in urban regions. The median of Staphylococcus sp. was 2.5 × 100 CFU/m3 in alpine areas and 7.5 × 100 CFU/m3 in urban and rural areas. Higher bacterial concentrations were measured in sunshine and in windy weather. A relationship was observed between the concentrations of airborne mesophilic bacteria and the coarse particles in all three areas. The present study determined values between 5.0 × 100 and 4.6 × 102 CFU/m3 as natural background concentrations of airborne mesophilic bacteria and 1.2 × 107 pa/m3 and 6.5 × 104 pa/m3 for fine and coarse particles, respectively. These results can be proposed as baseline for the assessment of the emission sources of mesophilic bacteria for summer and early autumn.