Rationale: Iron induces growth in bacteria such as P. Aeruginosa. This is the most abundant transition metal in ambient particulate matter (PM). Since it has been reported that air pollution increases chronic obstructive pulmonary disease (COPD) exacerbations, we hypothesize that iron content in PM will induce an increase in bacterial growth.

Methods: P. Aeruginosa strain, PAO1 cultures were grown in the presence of different iron-containing particles and iron chelators. More specifically, iron-containing particles of various sizes, composition and iron solubility were used. These included alpha and gamma Fe2O3, metallic iron nanoparticles, Fly Ash and various iron chelators such as lactoferrin. Growth was observed over time by sampling cultures and determining colony forming units (cfu).

Results: After six hours, PAO1 cultures in the presence of iron-containing particles grew one log more than PAO1 in the presence of particles without iron. Iron chelation prevented the iron-containing particles from induced PAO1 growth increase. Furthermore, smaller iron-containing particles induced greater increased growth in PAO1 compared to larger particles

Conclusion: This study provides clear evidence that PM is a potential source of iron for bacteria. In addition, it seems that particle size affects the PM induced bacterial growth. These results are significant since 75% of COPD exacerbations are considered bacterial and they show that PM is a potential source of iron for bacterial growth.