Collateral selective landscape of drug resistance in experimentally evolved biofilms of Pseudomonas aeruginosa

Wickham, Gregory (2021) Collateral selective landscape of drug resistance in experimentally evolved biofilms of Pseudomonas aeruginosa. Doctoral thesis, University of East Anglia.

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Biofilms represent a discrete form of microbial life which possess physiological distinctions from free-living planktonic counterparts which may also elicit lifestyle-dependent adaptive responses to selective pressures. In this work, an experimental evolution model is validated and used to study the evolutionary trajectories to antimicrobial resistance in biofilms of Pseudomonas aeruginosa. The serial passage of biofilms selected for biofilm hyperproduction which was characterised by increased biomass deposition and phenotypic diversification but was not associated with intrinsic resistance to antibiotics. The mechanisms by which this was achieved appeared to be through constitutive increase of intracellular c-di-GMP concentrations via mutations in the phosphodiesterase dipA, the yfiBNR signalling complex and bifunctional diguanylate cyclase/ phosphodiesterase morA, Next, whether biofilm and planktonic lineages took disparate evolutionary trajectories to resistance to the antipseudomonal antibiotics, ciprofloxacin, ceftazidime and tobramycin was investigated. For each antibiotic, resistant mutants from both lifestyles possessed conserved ‘driver’ mutations, however mechanistic distinctions between lifestyles were identified based on the repertoire of secondary mutations. This included efflux pump regulators, porins and biofilm-dependent pathways including type IV pili and alginate biosynthesis genes. Finally, the effect of adaptation to a panel of 48 antimicrobial agents including antibiotics, biocides and metals on biofilm formation, relative fitness and antimicrobial susceptibility was investigated. Over half of the selective agents were able to collaterally select for reduced susceptibility to antibiotics indicating that the widespread use of these agents may act as a driver of clinically-relevant drug resistance. Cross-resistant mutants arose through a variety of mechanisms, including constitutive expression of multidrug efflux, hypermutation, cell wall remodelling and porin loss. This work provides novel insights into the role of lifestyle in adaptation to selective pressures and the importance of collateral selective effects in the evolution of drug resistance.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Chris White
Date Deposited: 16 Nov 2022 13:34
Last Modified: 16 Nov 2022 13:34


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