Molecular Characterization of the Air Microbiome and Associated Toxicological Hazards in a Zoological Garden

This study presents the first comprehensive characterization of the airborne microbiome in a zoological garden and its comparison with the surrounding atmospheric environment. The aim of this study was to evaluate potential human health hazards associated with occupational and visitor exposure in zoo environments across 24 sampling locations. The assessment included measurements of particulate matter (PM) and gaseous pollutants, microbiological contamination of air, surfaces, settled dust, and selected items of personal protective equipment (PPE). In addition, the cytotoxic potential of settled dust samples was evaluated using A549 human lung epithelial cells. The highest concentrations of airborne PM ranged from 0.250 mg/m³ for PM₁ to 0.278 mg/m³ for PM₁₀. The concentrations of chemical contaminants varied depending on the sampling location. Airborne bacterial counts ranged from 1.1 × 10² to 3.0 × 10² colony-forming units (CFU)/m³ in employee areas and from 2.2 × 10³ to 1.5 × 10⁴ CFU/m³ in visitor areas. The average microbial contamination of surfaces in both employee and visitor areas was 4.3 CFU/cm². Amplicon sequencing revealed that the airborne microbiome was dominated by bacterial taxa belonging to Bacillota, Pseudomonadota, and Actinomycetota, as well as fungal taxa representing the phyla Ascomycota and Basidiomycota. Settled dust samples exhibited variable cytotoxicity toward A549 cells, with half-maximal inhibitory concentration (IC₅₀) values ranging from 13.1 to 53.5 mg/mL. The findings provide novel insights into the molecular composition of zoo-associated airborne microbial communities and their potential implications for environmental health risk assessment and hygiene management practices in zoological gardens.