249 - Roles of Ohr (a Cys based peroxidase) and OhrR (a redox regulated transcription factor) from Pseudomonas aeruginosa in a mouse infection model

Abstract

Pseudomonas aeruginosa is a human pathogen that represents a serious threat worldwide because they present resistance to several clinical relevant antibiotics. Pathogenic bacteria have evolved several defense strategies, including antioxidant mechanisms to overcome host responses. Organic hydroperoxide resistance protein (Ohr, a Cys-based peroxidase) and its transcriptional repressor (OhrR, a redox regulated transcription factor) comprise a system that is central in the defense of bacteria to organic hydroperoxides. To understand the role of Ohr/OhrR system in the virulence of P. aeruginosa, an acute pneumonia model in mice was used. Initially, the ∆ohr, ∆ohrR and ∆ohr/∆ohrR mutants of P. aeruginosa PA14 (WT) were constructed by homologous recombination. Female BALB/c mice (8–12 weeks old) were intratracheally inoculated with 60 µL of bacterial suspension (2×106 cells/ml) or PBS in the control group. After a 24 hour-infection, the lungs, spleen, liver and blood were harvested, and bacterial burden, pro-inflammatory cytokines and neutrophil recruitment were analyzed. No CFU difference was observed between the mice infected with the WT strain and mutants strains in the organs. Although, higher levels of TNF-α and IL-1β was observed in the lungs of mice infected with the ∆ohr, ∆ohrR and ∆ohr/∆ohrR mutants as compared to the wild-type infected ones, suggesting a pro-inflammatory processes. Notably, less neutrophil recruitment was observed in the lungs of animals infected with ∆ohrR, suggesting that overexpression of Ohr might promote anti-inflammatory responses in this area. Corroborating this data, an increased survival trend was observed in the ∆ohrR infected mice, suggesting a less virulent phenotype. Since hydroperoxides of arachidonic acid are modulators of inflammatory processes and are reduced by Ohr to alcohols at extremely high rates, it is tempting to speculate that Ohr/OhrR system may subvert host immune responses.