Finding the Achilles heel : investigating how to control major bacterial pathogens

Solsona Gaya, Maria (2024) Finding the Achilles heel : investigating how to control major bacterial pathogens. Doctoral thesis, University of East Anglia.

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Abstract

Biocides are critical in the control and prevention of healthcare-associated infections. The emergence of bacterial tolerance/resistance to biocides and cross-resistance to antibiotics is a potential concern. Understanding how nosocomial pathogens respond to biocidal agents is key to improving infection prevention and control products and practices.

An evolution model was used to study how Staphylococcus aureus and Enterococcus faecalis responded to challenge with commonly used biocides and a novel biocidal formulation. Biofilm and planktonic lineages were exposed to repeated sub-lethal concentrations of chlorhexidine digluconate (CHX) and octenidine dihydrochloride (OCT) when grown both planktonically and as a biofilm. Both pathogens could adapt to both biocides with planktonic lineages able to survive higher concentrations of CHX and OCT before growth was inhibited. Evolved isolates had no major fitness deficit and low-level changes to susceptibility to various other antimicrobials were observed after biocide exposure. RNA sequencing identified multiple pathways involved in envelope homeostasis changed expression after biocide exposure.

Sequencing of S. aureus mutants from independent lineages identified repeated loss of function changes within fatty acid kinase (fakA) after exposure to CHX and OCT in all conditions. Analogous changes were observed within the homologous gene (dak2) in parallel experiments with E. faecalis. Significantly lower ethidium bromide accumulation and differences in the cell envelope were observed in isolates with fakA mutation when compared to the WT, suggesting differences in membrane permeability and fluidity. A final evolution experiment with a novel biocidal formulation however identified no changes in genes known to confer biocide tolerance after exposure.

This work shows in vitro evolution methods can be highly informative in understanding mechanisms of action and bacterial responses to biocides, and has identified a novel important role of FakA in biocide susceptibility. Different biocides impart different selective impacts and future work is needed to understand bacterial responses to diverse biocides.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Medicine and Health Sciences > Norwich Medical School
Depositing User:	Zoe White
Date Deposited:	19 Sep 2024 16:37
Last Modified:	19 Sep 2024 16:46
URI:	https://ueaeprints.uea.ac.uk/id/eprint/96783
DOI:

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