Comparative analysis of airborne bacteria and fungi in two salt mines in Poland

The aim of this work was to determine the genera or species composition and the number of colony forming units of airborne bacteria and fungi, respectively, in two salt mines in Poland “Wieliczka” (Lesser Poland) and “Polkowice–Sieroszowice” (Lower Silesia). Both of them are working environments characterized by extreme conditions, and additionally “Wieliczka,” officially placed on the UNESCO World Heritage Sites’ list, plays a role of tourist attraction. There are also some curative chambers located in this mine. Air samples were taken once in December 2015, between 6:00 a.m. and 9:00 a.m. There were nine measurement points located about 200 m underground in “Wieliczka” and six measurement points located in the working shafts about 400 m underground in “Polkowice–Sieroszowice.” The total volume of each air sample was 150 L. Air samples, collected in individual measurement points of both salt mines, were inoculated on two microbiological media: potato dextrose agar and tryptic soy agar using the impact method. We identified 10 and 3 fungal genera in the “Wieliczka” Salt Mine and in “Polkowice–Sieroszowice,” respectively. The most common were fungi of the Penicillium genus. In both mines, the Gram-positive bacteria of genus Micrococcus were detected most frequently. Among identified microorganisms, there were neither pathogenic fungi nor bacteria. The most prevalent microorganisms detected in indoor air were Gram-positive cocci, which constituted up to 80% of airborne microflora. Our results showed that microorganisms recorded in the air samples are not a threat to workers, tourists or patients. Neither pathogens nor potentially pathogenic microorganisms, listed as BSL-2, BSL-3 or BSL-4, were detected. The microbes identified during our analysis commonly occur in such environments as the soil, water and air. Some of the detected bacteria are component of natural microflora of human skin and mucous membranes, and they can cause only opportunistic infections in individuals depending on their health condition.