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UBC Theses and Dissertations

Swarming motility in Pseudomonas aeruginosa : a complex adaptation with implications for antibiotic resistance and virulence Coleman, Shannon


Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen that possesses intrinsic antibiotic resistance. Highly adaptable, P. aeruginosa is capable of different forms of motility, including swarming, swimming, twitching and surfing. Swarming motility is a multicellular movement of cells across semisolid surfaces that is associated with complex adaptations including adaptive antibiotic resistance. Here a disc diffusion assay showed that swarming bacteria were resistant to multiple antibiotics, including aminoglycosides, β-lactams, chloramphenicol, ciprofloxacin, macrolides, tetracycline, and trimethoprim. RNA-Seq of swarming cells showed the dysregulation of 1,581 genes, including 104 regulatory factors, upregulated virulence and iron acquisition factors, and downregulated ribosomal genes. Forty-one mutants resistant to tobramycin under swarming conditions were found, including prtN, a regulator of pyocin, and wbpW, involved in LPS biosynthesis. RNA-Seq of swarming cells treated with tobramycin revealed the upregulation of the multidrug efflux pump mexXY. To investigate the role of swarming in vivo, a screen for swarming-specific mutants was performed, revealing ptsP, a regulator of carbon and nitrogen metabolism. The ∆ptsP mutant was deficient specifically in swarming but not swimming or twitching motility. Interestingly, ∆ptsP also had greatly reduced organ invasion in a mouse infection model, suggesting a likely role for swarming in vivo. Besides ptsP, small RNAs also regulated swarming motility, typically via post-transcriptional means. A screen of sRNA overexpressing strains revealed an sRNA, PA0805.1 that influenced diverse bacterial behaviours including swarming, swimming, twitching, cytotoxicity, adherence and tobramycin resistance. RNA-Seq and proteomics uncovered a broad regulatory profile with 1,121 differentially expressed genes and 925 proteins, including 118 regulatory factors, downregulated pilus genes, upregulated adherence and virulence factors, and upregulated multidrug efflux systems including mexXY and mexGHI-opmD. Another sRNA, PA2952.1, when overexpressed influenced swarming, swimming, and tobramycin, gentamicin and trimethoprim resistance. Transcriptomics and proteomics showed differential abundance of 784 genes and 445 proteins, encompassing 82 regulatory factors, downregulated pili, dysregulated flagellar genes, upregulated mexGHI-opmD and the upregulated arn operon involved in LPS modification. Overall this thesis has shown that swarming motility is a complex adaptation conferring multiple antibiotic resistance, that is regulated by sRNAs and coupled to virulence adaptations in vivo.

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