Understanding plasmid transfer in bacterial biofilms

Liu, Ho Yu (2025) Understanding plasmid transfer in bacterial biofilms. Doctoral thesis, University of East Anglia.

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Abstract

Antimicrobial resistance remains an enormous challenge, with the horizontal transfer of resistance genes between species a major contributor to the evolution of resistance. Most bacteria exist in polymicrobial biofilm communities, and biofilms have been suggested to encourage plasmid persistence and promote horizontal gene transfer. However, much current knowledge is based on experiments conducted using planktonic bacteria that are not representative of real-world bacterial communities. It remains unclear which environmental drivers impact horizontal gene transfer within polymicrobial biofilms, or which genes are involved in plasmid acquisition.

In this study, a multispecies biofilm conjugation model was developed to monitor the movement of pHYCTX14, a clinically relevant conjugative plasmid, between Escherichia coli and Salmonella enterica serovar Typhimurium. Using this model, the impact of a range of chemicals, including food preservatives and antimicrobials, on the rate of plasmid movement was investigated. The results indicated that the chemicals tested had very different impacts on conjugation efficiency, with the lowest conjugation efficiency obtained for experiments conducted under stress from sodium nitrite, and the highest obtained for experiments conducted under stress from copper sulphate.

Using a massively parallel transposon mutagenesis approach, TraDIS-Xpress, genes involved in the acquisition of pHYCTX14 in E. coli and S. Typhimurium were also identified. Key genes identified to be involved in plasmid acceptance included those associated with energy production, bacterial membrane structure, efflux and RNA polymerase recycling.

This work describes the development of a multispecies biofilm conjugation model to explore how external stress factors can influence the rate of plasmid movement within biofilms, and the use of TraDIS-Xpress to investigate the genes involved in host plasmid acceptance.

These experiments have laid the groundwork for further investigations into the evolution of antimicrobial resistance within multispecies biofilms and into developing a detailed insight into the host-plasmid interplay.

Keywords: Biofilms, antimicrobial resistance, plasmids, horizontal gene transfer, conjugation, TraDIS-Xpress

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Medicine and Health Sciences > Norwich Medical School
Depositing User:	Chris White
Date Deposited:	12 Feb 2026 13:04
Last Modified:	12 Feb 2026 13:04
URI:	https://ueaeprints.uea.ac.uk/id/eprint/101929
DOI:

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