Burkholderia cenocepacia requires complete lipopolysaccharide to resist bacterial killing agents

• Author / Creator

  Ruest, Marta K

• Antibiotic-resistant infections are a growing concern, if this issue is not addressed by the year 2050 these infections will cause ~10 million deaths per year. Traditional antibiotics targeting essential life processes have demonstrated a rapid rate of resistance development. Modern antibiotics should therefore focus on targeting non-essential processes to prevent or at least slow the development of resistance. For this reason, many researchers have placed emphasis on identifying drugs which target virulence processes of antibiotic-resistant bacteria. One process of interest is innate immune resistance as it is the first line of defense against invading pathogens. This study used human serum to simulate innate immune defense including antimicrobial peptides and the complement system. Bacteria have evolved a variety of serum-resistance factors which can be used as novel antibiotic targets. Burkholderia cenocecpacia is an extremely multi-drug resistant (MDR) opportunistic pathogen causing severe and lethal infections in patients with cystic fibrosis (CF). This bacterial species is also capable of producing highly fatal bloodstream infections. Many virulence factors have been characterized for B. cenocepacia yet research on complement-resistance is limited. The purpose of this thesis was to identify serum-resistance factors of B. cenocepacia and potential antibacterials with mechanisms of action involving these factors. Following a mutant library screen, a variety of serum-resistance factors were identified but genes relating to lipopolysaccharide (LPS) biogenesis were recovered with the highest frequency. The inner core portion of the LPS had previously been characterized as playing a role in complement-resistance of B. cenocepacia. However, this study confirmed that the entirety of the LPS is required for survival in the presence of serum in vitro and in vivo. It was also found that complete LPS is necessary for B. cenocepacia to resist the antibiotic colistin. Bacteriophages, or phages, are viruses of bacteria which have long been known to be capable of killing MDR bacteria. There has been a renewed interest in phages as a potential solution to the antibiotic resistance crisis. LPS is a common receptor for phages and following screening of a library of phages four were found to bind the LPS to initiate bacterial infection. Isolation and characterization of phage-resistant mutants revealed that they had truncated LPS and were sensitive to colistin. Combinations of colistin and LPS-binding phages were found to exhibit synergistic killing effects against B. cenocepacia likely through a phage steering mechanism. Altogether, this study associated several genes and their respective known/putative functions with B. cenocepacia’s ability to resist bacterial killing agents in serum. Additionally, a novel treatment combination targeting a serum-resistance factor was identified which has the potential to prevent B. cenocepacia from causing sepsis.

• Subjects / Keywords

  • Burkholderia cenocepacia
  • phage therapy
  • lipopolysaccharide
  • antibiotic resistance
  • phage-antibiotic synergy

• Graduation date

  Spring 2023

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-8pze-pc15

• 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.