The effect and mechanism of urban fine particulate matter (PM2.5) on horizontal transfer of plasmid-mediated antimicrobial resistance genes

Fine particulate matter (PM2.5) and antimicrobial resistance are two major threats to public health worldwide. Current air pollution studies rely heavily on the assessment of PM2.5 chemistry and toxicity. However, whether and how PM2.5 affects the proliferation and transfer of antimicrobial resistance genes (ARGs) in various environments has remained unanswered. This study investigated the effects and potential mechanisms of urban PM2.5 on the horizontal transfer of ARGs between opportunistic Escherichia coli (E. coli) strains. The results showed that urban PM2.5 samples collected from Xi'an (XA), Shanghai (SH), and Shijiazhuang (SJZ) in China induced location- and concentration-dependent promotion of conjugative transfer frequencies compared to the control group. The relevant mechanisms were also explored, including the formation of intracellular reactive oxygen species (ROS) and the subsequent induction of oxidative stress, SOS response, changes in membrane permeability, and alternations in mRNA expression of genes involved in horizontal transfer. This study highlights the effect of PM2.5 on promoting the horizontal transfer of ARGs and elucidates the mechanism of the antimicrobial-resistance risks posed by urban PM2.5. These findings are of great value in understanding the transmission of antimicrobial resistance in various environments and provide valuable information for re-evaluating air quality assessment practices.