Date of Graduation

12-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Cell & Molecular Biology (PhD)

Degree Level

Graduate

Department

Cell & Molecular Biology

Advisor/Mentor

Kwon, Young Min

Committee Member

Foley, Steven L.

Second Committee Member

Ricke, Steven C.

Third Committee Member

Rhoads, Douglas D.

Keywords

Salmonella enterica; Antimicrobial resistance

Abstract

The dynamic distribution of antimicrobial resistance genes in Salmonella enterica is considered a public health risk. S. enterica is one of the most important etiological agents of foodborne illness and has a critical impact on global human health. In S. enterica and related species, mobile genetic elements (MGEs) serve as primary vehicles for the dissemination of antibiotic resistance genes in the bacterial evolution. This dissemination can be impacted by different selective pressures that leads to diverse antibiotic response phenotypes. This project focusses on the dynamics of antimicrobial resistance genes, particularly exploring the transfer efficiency of multidrug resistance plasmids in S. enterica using a combination of in silico and in vitro techniques. Plasmid physiology is part of an essential genetic engineering tool has mediated the dynamic transfer and spread of antimicrobial resistance in Salmonella isolates. Several phenotypic and molecular techniques were selected in these studies to better understand the molecular biology and epidemiology of resistance plasmids. These methods included whole genome sequencing (WGS) analyses, replicon (incompatibility; Inc) typing and conjugation studies of plasmids from S. enterica and related species. Multiple in silico analyses were used to evaluate WGS and plasmid sequencing data to examine the distribution of MGEs, AMR, biocide, disinfectant, and heavy metal resistance genes across the different plasmid types and to develop a plasmid characterization database. The database supported the development of the computational algorithms to process the WGS data from S. enterica isolates and is very useful for identifying the plasmid Inc types and their specific conjugal transfer systems, which are valuable to study the diversity and dissemination of plasmids associated with AMR in S. enterica and other Enterobacteriaceae. In vitro studies explored the impact of different antimicrobial exposures on conjugal transfer potential of plasmids. For some S. enterica strains, exposure to different concentrations of tetracycline or chloramphenicol led to differences in the efficiency of AMR plasmid transfer. These data help to better understand the distribution of resistance genes and provide a useful method for a comprehensive molecular studies of plasmid transfer dynamics. The impact of these findings clarifies the role of the conjugation dynamics in the dissemination of antimicrobial resistance in S. enterica and related species, which can potentially impact the transfer of resistance genes within the gastrointestinal microbiome. Further studies are required to identify the underlying genetic mechanisms for Salmonella resistance plasmid transfer using approaches like RNA-sequencing methods to extend the understanding of the regulation of genetic pathways during conjugal transfer. Overall, the research study expands our knowledge of plasmid transfer dynamic and the provides tools that can be used to better understand AMR gene transfer among Salmonella enterica isolates which can have an impact in clinical and diagnostic laboratories as well as in epidemiological surveillance.

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