Characterization of phage-host interactions in Stenotrophomonas maltophilia

• Author / Creator

  McCutcheon, Jaclyn G

• Bacteriophages are highly abundant viruses that replicate within and effectively kill specific target bacterial hosts. The specificity of phages to their host relies on the presence of the correct cell surface receptor that is recognized by phage receptor binding proteins. These properties make phages desirable as an alternative to antibiotics for the treatment of multidrug resistant bacterial infections, a concept termed phage therapy that has gained renewed interest in recent years. One such bacterium of concern is Stenotrophomonas maltophilia, a Gram-negative opportunistic pathogen that is rapidly increasing in prevalence in hospital and community-acquired infections worldwide, due largely to its numerous innate antibiotic resistance mechanisms. To further develop phage therapy against S. maltophilia and address an overlooked aspect of phage characterization, I have identified the cellular surface receptor for eight S. maltophilia phages. Seven phages with Siphoviridae morphologies adhere to the major pilin subunit of the type IV pilus, a virulence factor that aids in motility, adherence to surfaces and biofilm formation. The eighth phage was identified to putatively interact with the TonB-dependent iron uptake protein, CirA, as a novel phage receptor. To further assess two of these phages as therapeutic candidates, I analyzed their complete genome sequences and phenotypic properties. Phage AXL1 was identified to encode resistance to the frontline antibiotic combination trimethoprim-sulfamethoxazole, whereas AXL3 is a novel virulent phage and candidate for genetic engineering. Additionally, I investigated the lack of in vivo data for S. maltophilia and show that type IV pili-binding phage DLP3 rescues Galleria mellonella larvae from lethal S. maltophilia infection. Further investigation into the mechanism of host interactions for the type IV pili binding phages identified the surface exposed αβ-loop of the major pilin protein as a structural region important for phage binding, as well as two tail proteins in phage DLP2 as putative receptor binding proteins for cross-genera bacterial infection. The identification of bacterial virulence factors as host receptors makes these phages promising candidates for an anti-virulence phage therapy strategy in which phage treatment creates a selective pressure for bacterial avirulence if phage resistant mutants arise.

• Subjects / Keywords

  • bacteriophage
  • Stenotrophomonas maltophilia
  • phage therapy
  • type IV pilus
  • receptor

• Graduation date

  Fall 2022

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-fvgh-f834

• License

  This thesis is made available by the University of Alberta Library 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.