Investigating the role of low-oxygen-activated (lxa) encoded proteins in the pathogenesis of Burkholderia cepacia complex and their contribution to chronic infection in cystic fibrosis

Abstract

Burkholderia cepacia complex (Bcc) is a group of 22 closely related species of Gram-negative bacteria that cause chronic infections in people with cystic fibrosis (CF) that are rarely eradicated. The high-level antibiotic resistance and poorly understood mechanisms by which Bcc survive and persist during chronic infection mean that combatting these chronic infections is particularly challenging. We have previously found that a group of 20 low-oxygen-activated (lxa) encoded proteins were consistently upregulated in sequential Bcc isolates in two chronically infected CF patients over time of infection. Many of these proteins have not previously been studied in Bcc but the consistent upregulation over time of infection suggests that they play an important role during chronic infection. Two particular proteins of interest within the lxalocus that were consistently upregulated were a universal stress protein (USP) and a phospholipid binding protein (PBP). Single gene deletion mutants (Δusp and Δpbp) in the wildtype Bcc strain K56-2 (WT) both showed a 90 % reduction in attachment to CFBE41o- cells compared to WT. There was also a 5-fold reduction in the virulence of Δpbp in the acute infection model Galleria mellonella (P<0.005) and an increased sensitivity of Δusp to peroxide-induced oxidative stress (P<0.0001) and low pH (P<0.05) relative to WT. A reduction in both uptake and survival of Δusp in U937 macrophage-like cell line compared to WT, suggests the USP plays a role in the intra-macrophage survival of Bcc. Overall, these proteins, previously associated with low-oxygen conditions may play a considerable role in Bcc pathogenesis and its adaption during chronic infection.