Rangama, Marie Séverine (2020) Characterisation of a subset of Escherichia coli river isolates and their role in the environmental resistome. PhD thesis, University of Warwick.

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Abstract

Infections caused by antimicrobial resistant bacterial pathogens are fast becoming an important global health issue. Our research group have identified wastewater treatment plants (WWTPs) as hotspots for the dissemination of antimicrobial resistant
genes/bacteria (ARG/ARB) into the environment. Specifically, strains of E. coli ST131 carrying multiple resistance genes including blaCTX-M-15 (encoding extended spectrum beta-lactamase, ESBL).

Previous work produced isolates from a local river which included E. coli ST131 strain 48 downstream of a WWTP and harbouring blaCTX M-15, blaOXA and blaTEM in its genome. Through conjugation with a donor strain the plasmid was isolated and
sequenced and found to harbour the blaCTX-M-15 and blaTEM. The de novo assembly of the plasmid was achieved using long-reads sequences by using a new bioinformatic pipeline and showed the blaCTX-M-15 was the only resistance gene located on this
plasmid.

The data revealed that the strain 48 expressed and secreted an ESBL that provided a protective effect against cefotaxime for susceptible cells. In silico analysis predicted a signal peptide for CTX-M-15 and TEM. Exoproteomics and whole-cell proteomics
identified CTX-M-15 as the major secreted ESBL, confirming in silico analysis. Heterologous expression of the blaCTX-M-15 gene in another E. coli strain confirmed that this gene was responsible for the observed protective effect against cefotaxime. It becomes clear that the plasmid pSRJ48c was highly beneficial to strain 48 and persisted in absence of selection indicated a balance between plasmid cost and benefit. An evolutionary hypothesis on the co-evolution of host and plasmid support these
observations.

The survival of strain 48 under prolonged anaerobic digestion in the presence and absence of a third-generation cephalosporin was investigated and provided evidences of the survival of the E. coli 48 and the persistence of blaCTX-M-15 through a nine-day
anaerobic incubation. The sensitive commensal strain failed to survive both in presence and the absence of the antibiotic. The survival of 48 poses multiple risks to human health as this strain has the potential to be the host for other ARGs and can contribute to the spread of ARGs.

Overall, the work developed in this thesis suggests that more rigorous controls of AD parameters should be employed to reduce survival of ARB. Further work could lead to the optimisation of the process for AD both for human and animal waste.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QH Natural history > QH426 Genetics Q Science > QR Microbiology R Medicine > RM Therapeutics. Pharmacology
Library of Congress Subject Headings (LCSH):	Escherichia coli, Drug resistance in microorganisms, Anti-infective agents, Mobile genetic elements
Official Date:	June 2020
Dates:	Date Event June 2020 Submitted
Institution:	University of Warwick
Theses Department:	School of Life Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Wellington, E. M. H. (Elizabeth M. H.) ; Hawkey, P. M. (Peter M.)
Extent:	xi, 144 leaves : illustrations, charts
Language:	eng

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