Abstract
BackgroundBurkholderia cepacia complex bacteria are opportunistic pathogens, which can cause severe respiratory tract infections in patients with cystic fibrosis (CF). As treatment of infected CF patients is problematic, multiple preventive measures are taken to reduce the infection risk. Besides a stringent segregation policy to prevent patient-to-patient transmission, clinicians also advise patients to clean and disinfect their respiratory equipment on a regular basis. However, problems regarding the efficacy of several disinfection procedures for the removal and/or killing of B. cepacia complex bacteria have been reported. In order to unravel the molecular mechanisms involved in the resistance of biofilm-grown Burkholderia cenocepacia cells against high concentrations of reactive oxygen species (ROS), the present study focussed on the transcriptional response in sessile B. cenocepacia J2315 cells following exposure to high levels of H2O2 or NaOCl.ResultsThe exposure to H2O2 and NaOCl resulted in an upregulation of the transcription of 315 (4.4%) and 386 (5.4%) genes, respectively. Transcription of 185 (2.6%) and 331 (4.6%) genes was decreased in response to the respective treatments. Many of the upregulated genes in the NaOCl- and H2O2-treated biofilms are involved in oxidative stress as well as general stress response, emphasizing the importance of the efficient neutralization and scavenging of ROS. In addition, multiple upregulated genes encode proteins that are necessary to repair ROS-induced cellular damage. Unexpectedly, a prolonged treatment with H2O2 also resulted in an increased transcription of multiple phage-related genes. A closer inspection of hybridisation signals obtained with probes targeting intergenic regions led to the identification of a putative 6S RNA.ConclusionOur results reveal that the transcription of a large fraction of B. cenocepacia J2315 genes is altered upon exposure of sessile cells to ROS. These observations have highlighted that B. cenocepacia may alter several pathways in response to exposure to ROS and they have led to the identification of many genes not previously implicated in the stress response of this pathogen.
Highlights
Burkholderia cepacia complex bacteria are opportunistic pathogens, which can cause severe respiratory tract infections in patients with cystic fibrosis (CF)
Treatment of B. cenocepacia J2315 biofilms with H2O2 and NaOCl Previous research indicated that disinfection protocols based on the use of H2O2 (3%, 30 min) and NaOCl (0.05%, 5 min) have insufficient activity against B. cenocepacia biofilms [7]
Transcriptomic response to high levels of oxidative stress: microarray data analysis Compared to the normalized signal intensities obtained for the untreated B. cenocepacia J2315 sessile cells, the normalized signal intensity for 618 (6.0%) and 854 (8.3%) probes was significantly altered after treatments with H2O2 and NaOCl, respectively (Table 1)
Summary
Burkholderia cepacia complex bacteria are opportunistic pathogens, which can cause severe respiratory tract infections in patients with cystic fibrosis (CF). As several outbreaks with genetically distinct B. cepacia complex strains have occurred, stringent infection control guidelines were brought into force; these guidelines aim to segregate infected patients from non-infected ones, and emphasize the importance of good hand hygiene practices and frequent disinfection of environmental surfaces and respiratory equipment [6]. Biofilm formation has been described for several B. cepacia complex strains and is considered to be an important virulence trait [5] The observation that these sessile cells are highly resistant against H2O2 and NaOCl is worrying since these oxidative agents are very important in the endogenous defence against microorganisms. H2O2 and NaOCl can react with intracellular iron via the Fenton reaction and the resulting highly reactive hydroxyl radicals will damage lipids, proteins and DNA [9,10]
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