Exosome‐Associated Iron Release during Respiratory Virus Co‐Infection Enhances Pseudomonas aeruginosa Biofilm Growth

Abstract

Clinical observations link respiratory virus infection and colonization with the opportunistic pathogen Pseudomonas aeruginosa in Cystic Fibrosis (CF) patients, but the mechanism underlying this interaction is not understood. The transition of P. aeruginosa from an acute to chronic infection often involves the development of highly antibiotic resistant biofilm communities in the lung, which contribute to disease progression in patients. We hypothesized that respiratory viral co‐infection promotes P. aeruginosa biofilm growth. Using a novel live‐cell imaging model, we observed that in the presence of respiratory syncytial virus (RSV) co‐infection, P. aeruginosa biofilm formation on airway epithelial cells (AECs) is significantly increased. The innate immune response to virus infection, measured by type III interferon (IFN‐λ) production, peaks at the same time as virus‐induced biofilm growth, and interestingly, treatment of AECs with IFN‐λ replicates the enhanced biofilm formation observed during virus co‐infection. The biofilm stimulatory activity was isolated to purified exosomes in conditioned media obtained from apical membrane of AECs infected with RSV. Conditioned media from RSV‐infected AECs was observed to have significantly increased levels of iron, and iron levels were also elevated in bronchoalveolar lavage fluid obtained from mice infected with RSV, suggesting that RSV infection disrupts host iron homeostasis in the airway epithelium. Iron is an essential nutrient for P. aeruginosa growth and biofilm maturation, and chelation of iron inhibits biofilm growth on human AECs. Although virus infection did not change the abundance of iron transporters in AECs, RSV did enhance apical secretion of exosome‐associated transferrin, a host iron‐binding protein previously shown to promote P. aeruginosa biofilm growth. Depleting transferrin from conditioned media blocked the biofilm stimulatory effect of RSV co‐infection. We are currently investigating the mechanism by which interferon signaling induces transferrin packaging and secretion in exosomes to stimulate P. aeruginosa biofilm growth. The antiviral interferon response to respiratory viral infection enhances susceptibility to secondary bacterial infections, and our data suggest a novel mechanism by which these pathways contribute to the development of chronic pulmonary P. aeruginosa infections. Moreover, these studies increase our understanding of how the host contributes to pathogen persistence in the airway.Support or Funding InformationThis work was supported by NIH K99/R00HL098342, P30DK072506, R56HL123771 and CFF Research Grant (JMB).