Klebsiella pneumoniae type VI secretion system: antimicrobial resistance, and virulence genes dissemination

Abstract

Klebsiella pneumoniae is recognised by the World Health Organisation as an urgent threat to human health, due to increasing isolation of multidrug resistant strains. Alongside the emergence of multidrug resistant strains, simultaneously there is increasing emergence of hypervirulent K. pneumoniae strains, that cause severe infection in healthy human hosts. Acquisition of antimicrobial resistant and virulence genes rapidly occurs by a mechanism of horizontal gene transfer called conjugation.

The type VI secretion system (T6SS) largely contributes to microbial antagonism and mediates interactions with host eukaryotic cells. K. pneumoniae T6SS behaviour and regulation is currently not extensively understood. In this study, we characterised a novel T6SS regulator of K. pneumoniae, Klebsiella pneumoniae T6SS regulator A (KtrA). A single amino acid change at position 6 of the KtrA sequence governs T6SS behaviour in a diverse range of isolates, thereby dictating interactions with neighbouring cells.

Furthermore, KtrA alters phoP expression, a positive regulator of K. pneumoniae T6SS. Regulation of PhoPQ is governed by the amino acid encoded at position 6 of KtrA. KtrA increases expression of bdcA. BdcA alters phoP expression in Kp43816 and alters intracellular NADPH levels in K. pneumoniae.

We demonstrate that T6SS behaviour dictates mobilisation of antimicrobial resistance and virulence genes to K. pneumoniae. An upregulated T6SS mediates killing of neighbouring cells, limiting conjugation and thereby mobilisation of both antimicrobial resistance and virulence genes. However, a downregulated T6SS results in reduced killing of neighbouring cells, facilitating conjugation and mobilisation of antimicrobial resistance and virulence genes.

In conclusion, we have uncovered a molecular switch for T6SS behaviour in K. pneumoniae. T6SS behaviour is crucial in determining the mobilisation and thereby dissemination of antimicrobial resistance and virulence genes in K. pneumoniae. These mechanistic insights are crucial in understanding the emergence and rapid spread of multidrug resistant and hypervirulent K. pneumoniae, that are an urgent threat to public health.

Thesis is embargoed until 31st December 2025.

Date of Award	Dec 2024
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy
Supervisor	Jose Bengoechea (Supervisor) & Miguel A. Valvano (Supervisor)