Composition of Culturable Microorganisms in Dusts Collected from Sport Facilities in Finland during the COVID-19 Pandemic

Abstract

Sport facilities represent extreme indoor environments due to intense cleaning and disinfection. The aim of this study was to describe the composition of the cultivated microbiota in dust samples collected in sport facilities during the COVID-19 pandemic. A dust sample is defined as the airborne dust sedimented on 0.02 m² within 28 d. The results show that the microbial viable counts in samples of airborne dust (n = 9) collected from seven Finnish sport facilities during the pandemic contained a high proportion of pathogenic filamentous fungi and a low proportion of bacteria. The microbial viable counts were between 14 CFU and 189 CFU per dust sample. In seven samples from sport facilities, 20-85% of the microbial viable counts were fungi. Out of 123 fungal colonies, 47 colonies belonged to the potentially pathogenic sections of Aspergillus (Sections Fumigati, Nigri, and Flavi). Representatives of each section were identified as Aspergillus fumigatus, A. flavus, A. niger and A. tubingensis. Six colonies belonged to the genus Paecilomyces. In six samples of dust, a high proportion (50-100%) of the total fungal viable counts consisted of these potentially pathogenic fungi. A total of 70 isolates were considered less likely to be pathogenic, and were identified as Aspergillus section Nidulantes, Chaetomium cochliodes and Penicillium sp. In the rural (n = 2) and urban (n = 7) control dust samples, the microbial viable counts were >2000 CFU and between 44 CFU and 215 CFU, respectively, and consisted mainly of bacteria. The low proportion of bacteria and the high proportion of stress tolerant, potentially pathogenic fungi in the dust samples from sport facilities may reflect the influence of disinfection on microbial communities.

Keywords: Aspergillus; Paecilomyces; airborne dust; potential pathogens; sport facilities.

Figure 1

Football then and now. This figure illustrates the movement of physical activities indoors. Left panel: Depiction of health education in Finland from the first half of the 20th century, which stressed the benefits of outdoor exercises for the prevention of tuberculosis [3]. Right panel: Modern football players inside a built environment, possibly avoiding traffic air pollution in urban air and the effects of the outdoor climate (snow and rain) in Finland (photo: Sanna Sulopuisto).

Figure 2

Densities of particles of 11 settled dusts captured in light microscope (400×). Airborne dust samples SF1-SF7 were collected by sedimentation into Petri plates from sport facilities. The reference dusts RD1 and RD2 were collected from a hay barn and an old summer house. Each dust sample (collected in three fallout plates) was suspended in 2 mL phosphate-buffered saline (PBS). Some 10 µL of the suspension was examined in five microscopic fields. The view shown in each picture is representative of the recorded views in the five examined microscopic fields, thus representing an average view of each dust.

Figure 3

Identification of the isolates from dust samples collected from sport facilities considered as potentially pathogenic based on their ability to grow at 37 °C and neutral pH. From each section and genus, selected strains from different samples were identified using molecular methods. The codes for the dust samples from the different sport facilities are shown in parentheses (SF2-SF7).

Figure 4

Identification of the isolates from the rural control dust samples, a hay barn (CD1) and a summer house (CD2). The 30 isolates growing at 37 °C were from the barn; the summer house contained no isolates growing at 37 °C.

Figure 5

The experimental design for comparison of the fungal and bacterial colony counts in settled air-borne dusts and for screening for potentially pathogenic fungi. Pathogenic potential was indicated by growth on tryptic soy agar (TSA) at 37 °C.

Figure 6

The outside (panels A–C) and inside (panels a–c) views of the urban and rural buildings examined in this study. Panels A and a represent views of an urban sport facility in Helsinki. The further panels show the two rural reference buildings, a hay barn (B,b), collection site for dust CD1, and a rural summer house (C,c), collection site for dust CD2. (Panels D,d) shows views of an urban educational building in Espoo.

Figure 7

Cultivation of a sample of sedimented dust. The dust collected from each sample was suspended in 2.1 mL PBS, and 100 µL was applied on the first vertical row of plates. The liquid was spread with the cotton swab on the first plate, the next two plates were wiped with the same swab.