Diversity of Bioaerosols in Selected Rooms of Two Schools and Antibiotic Resistance of Isolated Staphylococcal Strains (Bydgoszcz, Poland): A Case Study

The present study is aimed at evaluating microbiological air pollution in libraries, cafeterias and selected classrooms of two schools in Bydgoszcz city, northern Poland and determining the antibiotic resistance of Staphylococcal strains isolated from the indoor air. One of the investigated schools (School A) is located in the very center of the city, in the vicinity of a park, among old houses and stone-lined streets, while the other (School B), among modern residential buildings, close to a street with heavy traffic. In each school, air samples were collected in the morning, always from all three sampling sites, using the MAS-100 sampler. Selective growth media were used for bacteria and mold isolation and quantifying analysis. The antibiotic resistance of the isolated mannitol-positive staphylococci was assessed using the disc diffusion method in accordance with EUCAST recommendations. The highest mean concentration of heterotrophic bacteria was recorded in the cafeterias: 884 CFU m⁻³ in School A and 1906 CFU m⁻³ in School B. Molds were the most abundant in the library and cafeteria in School B, where their average concentration exceeded 300 CFU m⁻³. <i>Cladosporium</i> and <i>Penicillium</i> species prevailed, while <i>Fusarium</i>, <i>Acremonium</i> and <i>Aspergillus</i> were less abundant. Airborne mannitol-positive staphylococci were recorded at low concentrations, ranging from 6 to 11 CFU m⁻³ on average. According to the taxonomic analysis, <i>Staphylococcus aureus</i> isolates were the most abundant in both schools, followed by <i>S. xylosus</i>, <i>S. haemolyticus</i> and <i>S. saprophyticus</i>. The antibiograms indicated that resistance to erythromycin was common in 62.5% of the isolated staphylococcal strains. Levofloxacin and gentamicin were the most effective antibiotics. No multidrug-resistant strains were identified.