Identification and Characterization of Virulence Factors in the Principal Pathogenic Species of the Burkholderia cepacia complex

• Author / Creator

  Thomson, Euan Lewis Sproull

• Cystic fibrosis (CF) is the most common heritable disease among Caucasian populations, with afflicted individuals experiencing a immune, respiratory and digestive system complications. Compromised mucus clearance from the CF airway provides a habitat for bacteria and generates oxygen gradients within the mucus. Members of the Burkholderia cepacia complex (Bcc) are devastating airway pathogens of CF patients, with innate antibiotic resistance and the propensity to establish invasive necrotic infections. Their mechanisms of infection remain largely uncharacterized, though a number of virulence factors have been identified using standard model hosts. Among these factors are gene products common in human pathogens, interlaced by a complex regulatory network comprising global regulators, communication networks and environmental sensors. The objective of this study is to identify and detail virulence elements of the most prevalent Bcc species in the CF community using established model systems and a novel high-throughput plant host, Lemna minor (Common duckweed). First, a strong correlation was found between the relative virulence of Bcc strains in duckweed and the established insect model, Galleria mellonella (Greater wax moth larva). A non-ribosomal peptide synthestase gene cluster was identified in B. vietnamiensis and shown to cause erythocyte lysis and contribute to virulence in the larval model. To identify virulence factors in B. cenocepacia, 5,980 plasposon mutants were screened for attenuation against duckweed. Several novel virulence factors were found, including a regulator, a putative DNA binding protein, and metabolism-related proteins. Type VI secretion was studied for its contribution to B. cenocepacia virulence, but showed only antibacterial activity against Escherichia coli, suggesting a role for Bcc type VI secretion in competitive colonization of the CF lung. Finally, the engimatic B. multivorans, which demonstrates negligible virulence effects in most model hosts but accounts for nearly half of Bcc infections in CF, demonstrated virulence activation in both low oxygen and high temperature, indicating a regulatory effect of these CF-relevant environmental cues akin to the recently-identified lxa locus in B. cenocepacia. This finding indicates that standard infection models may be insufficient for characterizing this pathogen, and approaches that allow modified environmental conditions may be required to fully understand Bcc pathogenesis.

• Subjects / Keywords

  • Lemna minor
  • Virulence factors
  • Burkholderia cepacia
  • Low oxygen
  • Non-ribosomal peptide synthetase
  • Type VI secretion
  • Hemolysin
  • Duckweed

• Graduation date

  Fall 2013

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3H70866T

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.