Background: Coal Fly Ash (CFA) is a byproduct of coal combustion and is a potential source of iron released into the atmosphere. Iron is a key nutrient for bacterial growth and virulence. Airway surface liquid has different mechanisms to lower iron to prevent bacterial
colonization and infection. Since air pollution is correlated with increases in respiratory infections, we hypothesize that iron content in CFA will induce an increase in bacterial growth and virulence and inhibit antimicrobial peptide activity (AMP).

Methods: P. Aeruginosa strain, PAO1 cultures were grown in iron depleted media (M9), CFA from various sources (10μg/mL), and aluminum oxide particles (Al2O3). Growth was measured by recording OD600. In order to test virulence, Drosophila Melanogaster was poked with PAO1 with or without 10μg/mL CFA and survival was recorded over time. CFA was also incubated with pysiologically relevant concentrations of AMPs in the airway surface liquid (lysozyme, lactoferrin and β-Defensins 1 & 2) and combined with bacteria. Growth was recorded to determine AMP activity.

Results: After eight hours, PAO1 cultures in the presence of CFA grew more than PAO1 in the absence of iron (Al2O3). CFA also decreased survival in a Drosophila model of virulence when compared with control conditions (M9 alone and Al2O3). When incubated with physiologically relevant concentrations of AMPs, CFA inhibited AMP activity.

Conclusion: This study provides clear evidence that CFA is a potential source of iron for bacterial growth and virulence and inhibits AMP activity. These results provide a mechanism by which ambient particulate matter increases the risk of respiratory infections.