Pseudomonas aeruginosa Siderophores Damage Lung Epithelial Cells and Promote Inflammation.

Multidrug-resistant Pseudomonas aeruginosa is a common nosocomial respiratory pathogen that continues to threaten the lives of mechanically-ventilated patients in intensive care units and those with underlying comorbidities such as cystic fibrosis or chronic obstructive pulmonary disease. For over 20 years, studies have repeatedly demonstrated that the major siderophore pyoverdine is an important virulence factor for P. aeruginosa in invertebrate and mammalian hosts in vivo . Despite its physiological significance, an in vitro , mammalian cell culture model to characterize the impact and the molecular mechanism of pyoverdine during infection has only recently been developed. In this study, we adapt a previously-established murine macrophage-based model for human bronchial epithelial cells. We demonstrate that pyoverdine-rich conditioned medium from P. aeruginosa disrupts epithelial integrity in a manner that depends on protease activity and the type II secretion system. Disrupting pyoverdine production, whether genetically or chemically, mitigates this damage. Interestingly, this damage did not require exotoxin A or PrpL (protease IV), two previously-characterized toxins regulated by pyoverdine. We also examined the effects of exposure to purified pyoverdine on lung epithelial cells. While pyoverdine accumulates within cells, the siderophore is largely sequestered inside early endosomes, showing little cytotoxicity. This is in contrast to other, more membrane-permeable iron chelators and siderophores such as pyochelin. However, pyoverdine may indirectly contribute to lung inflammation by potentiating these iron chelators in promoting the production of proinflammatory cytokines.