Toxic mechanisms and biomarkers of Staphylococcus aureus aerosol exposure to human respiratory cells at the air-liquid interface.

Staphylococcus aureus is a major opportunistic pathogen in humans; airborne exposure to this bacterium is associated with increased respiratory disease incidence. The airway epithelium, serving as the primary barrier against inhaled pathogens, is particularly vulnerable to bacterial invasion. However, the underlying mechanisms and relevant biomarkers for this exposure remain underexplored. In this study, we evaluated the toxic effect mechanisms and biomarkers of S. aureus aerosol exposure to human bronchial epithelial (16HBE) cells at the air-liquid interface using microRNA (miRNA) sequencing. We found that exposure to aerosols containing 3.21 × 105 to 6.54 × 106 CFU/m3S. aureus impaired cell viability and proliferation, induced mitochondrial damage, and triggered inflammation by upregulating IFN-γ expression. The bacterium secreted pore-forming toxins, coagulases, nucleases, enterotoxins, and β-hemolysins to lyse cells and induced a cytokine storm by modulating the expression of hla, coa, nuc, sea, and hlb genes. 16HBE cells primarily upregulated Toll-like receptors (TLR1 and TLR5), mucins (MUC1), and epidermal growth factor receptors (KGF7 and TEP1) to recognize invasion, activate the immune response, and protect the cell membrane. miRNA sequencing suggested that medium-concentration exposure induced more differentially expressed genes (DEGs), particularly downregulated DEGs, than other concentrations. Twelve miRNAs uniquely shared across the exposure groups were considered potential biomarkers of S. aureus aerosol exposure. Regulatory networks analysis showed that miR-19a-3p, miR-18a-5p, miR-106b-5p, and miR-142-5p could influence cancer-related pathways and the MAPK signaling pathway by targeting genes such as CRK, NCOA3, MAPK1, and TGFR2 and may serve as biomarkers of 16HBE cell damage. Overall, this study elucidates the injury mechanisms and potential biomarkers of S. aureus aerosol exposure in respiratory cells, advances the understanding of airborne pathogen-induced toxicity.