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Numerous studies have linked a wide range of diseases including respiratory illnesses to harmful particulate matter (PM) emissions indoors and outdoors, such as incense PM and industrial PM. Because of their ability to penetrate the lower respiratory tract and the circulatory system, fine particles with diameters of 2.5 µm or less (PM2.5) are believed to be more hazardous than larger PMs. Despite the enormous number of studies focusing on the intracellular processes associated with PM2.5 exposure, there have been limited reports studying the biophysical properties of cell membranes, such as nanoscale morphological changes induced by PM2.5. Our study assesses the membrane topographical and structural effects of PM2.5 from incense PM2.5 exposure in real time on A549 lung carcinoma epithelial cells and SH-SY5Y neuroblastoma cells that had been fixed to preclude adaptive cell responses. The size distribution and mechanical properties of the PM2.5 sample were characterized with atomic force microscopy (AFM). Nanoscale morphological monitoring of the cell membranes utilizing scanning ion conductance microscopy (SICM) indicated statistically significant increasing membrane roughness at A549 cells at half an hour of exposure and visible damage at 4 h of exposure. In contrast, no significant increase in roughness was observed on SH-SY5Y cells after half an hour of PM2.5 exposure, although continued exposure to PM2.5 for up to 4 h affected an expansion of lesions already present before exposure commenced. These findings suggest that A549 cell membranes are more susceptible to structural damage by PM2.5 compared to SH-SY5Y cell membranes, corroborating more enhanced susceptibility of airway epithelial cells to exposure to PM2.5 than neuronal cells. SICM · Particulate matter · Membrane topography · Single-cell imagingmore » « less
Biofilm production is a key virulence factor that facilitates bacterial colonization on host surfaces and is regulated by complex pathways, including quorum sensing, that also control pigment production, among others. To limit colonization, epithelial cells, as part of the first line of defense, utilize a variety of antimicrobial peptides (AMPs) including defensins. Pore formation is the best investigated mechanism for the bactericidal activity of AMPs. Considering the induction of human beta-defensin 2 (HBD2) secretion to the epithelial surface in response to bacteria and the importance of biofilm in microbial infection, we hypothesized that HBD2 has biofilm inhibitory activity. We assessed the viability and biofilm formation of a pyorubin-producing Pseudomonas aeruginosa strain in the presence and absence of HBD2 in comparison to the highly bactericidal HBD3. At nanomolar concentrations, HBD2 – independent of its chiral state – significantly reduced biofilm formation but not metabolic activity, unlike HBD3, which reduced biofilm and metabolic activity to the same degree. A similar discrepancy between biofilm inhibition and maintenance of metabolic activity was also observed in HBD2 treated Acinetobacter baumannii, another Gram-negative bacterium. There was no evidence for HBD2 interference with the regulation of biofilm production. The expression of biofilm-related genes and the extracellular accumulation of pyorubin pigment, another quorum sensing controlled product, did not differ significantly between HBD2 treated and control bacteria, and in silico modeling did not support direct binding of HBD2 to quorum sensing molecules. However, alterations in the outer membrane protein profile accompanied by surface topology changes, documented by atomic force microscopy, was observed after HBD2 treatment. This suggests that HBD2 induces structural changes that interfere with the transport of biofilm precursors into the extracellular space. Taken together, these data support a novel mechanism of biofilm inhibition by nanomolar concentrations of HBD2 that is independent of biofilm regulatory pathways.more » « less