Deciphering the role of poly-n-acetyl-glucosamine in klebsiella pneumoniae
File(s)
Author(s)
Bradshaw, Jonathan
Type
Thesis
Abstract
The exopolysaccharide Poly-N-Acetyl-Glucosamine (PNAG) is almost ubiquitously expressed across bacteria, pathogens and commensals alike. As a result, PNAG is considered a potential broad-spectrum vaccine antigen, that could, in theory, protect against infections from diverse bacterial pathogens. However, characterisation of when and how PNAG is produced across most bacteria is not well understood, limiting our ability to evaluate PNAG as an antigenic target. This is exemplified in the Gram-negative critical priority pathogen Klebsiella pneumoniae (KP), which, despite encoding the PNAG biosynthetic machinery, has yielded unconvincing results during PNAG immunochemical detection assays. As a conserved bacterial antigen, we must also consider that PNAG-targeting therapies pose the risk of exhibiting off-target effects on the host microbiome. In this thesis, I address these questions, providing a detailed characterisation of PNAG production in KP and evaluating the impact of vaccination with PNAG on the gut microbiome. Firstly, I demonstrate that KP produces PNAG as large extracellular networks in vitro, but this switches to a cell-associated phenotype during severe in vivo lung infection. Then, by analysing a collection of high-risk KP genomes, we uncover a novel positive regulator of PNAG production located upstream of pgaA, which I re-name pgaR. Across a high-risk KP lineage, we see the repeated emergence of isolates lacking PNAG, via deletions and truncations in the pgaR and pgaA genes, as well as PNAG hyper-producing strains, which harbour a G>A substitution in the pgaR promoter. Finally, I demonstrate that vaccination with de-acetylated PNAG vaccine glycoconjugates does not impact the faecal or mucosa-associated microbiome. Ultimately, this highlights PNAG as an attractive KP antigen that has no off-target effects on the microbiome.
Version
Open Access
Date Issued
2025-09-24
Date Awarded
2026-03-01
Copyright Statement
Attribution-NonCommercial 4.0 International Licence (CC BY-NC)
License URL
Advisor
Frankel, Gad
Romano, Maria
Sponsor
Biotechnology and Biological Sciences Research Council (Great Britain)
Grant Number
BB/W5101154/1
Publisher Department
Department of Life Sciences
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)