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Natural Drivers of Antimicrobial Resistance

Hutton, William (2022) Natural Drivers of Antimicrobial Resistance, Thesis (Doctoral), Liverpool School of Tropical Medicine.

W Hutton - Thesis - Corrections - Complete.pdf - Accepted Version

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Antibiotic resistance is a serious ongoing threat to both the medical and agricultural sectors, with far-reaching and diverse consequences. Historically, antibiotic resistance has been thought to be driven by the anthropogenic use of antibiotics in clinical and agricultural settings. However, there is a growing body of evidence that clearly demonstrates that antimicrobial resistance developed naturally, millions of years ago. Understanding these natural drivers of antibiotic resistance is key to managing the ongoing antimicrobial resistance problem.
One potential natural driver of antibiotic resistance are phytochemicals which are chemicals produced by plants for environmental interaction. Phytochemicals are being explored for their potential role as antibiotic replacements in the clinic, and in agriculture. We propose that the use of phytochemicals as antimicrobial replacements in multiple industries will have an equal, or worse impact on the problem of antibiotic resistance, due to their potential to select for cross-resistance to other antimicrobials such as antibiotics. Phytochemicals could drive antibiotic resistance in one of three ways: (1) The selection of genes which confer cross resistance to antibiotics. (2) The selection of plasmids carrying both phytochemical and antibiotic resistance genes and (3) the selection of bacteria which are known antimicrobial resistance reservoirs.
In this study, two antimicrobial phytochemicals, quercetin and berberine were explored for their role as natural drivers of antibiotic resistance.
This study was split into three different experimental methodologies. The first experimental methodology developed a novel phytochemical screening assay, which was then successfully used to screen an oral metagenomic library, and the Swab and Send bacterial isolate library. Screening the metagenomic library uncovered three isolates with tolerance to either quercetin or berberine. These isolates contained inserts with multiple antibiotic resistance genes, including a glycosyltransferase and transpeptidase. Screening the Swab and Send library uncovered 20 isolates from 11 bacterial species containing antibiotic resistance genes with a phytochemical tolerant phenotype.
The second experimental methodology evolved P. aeruginosa NCTC 7244 and NCTC 9433 in sub-inhibitory concentrations of the phytochemicals for 30 days. This experiment was conducted see how environmental bacteria responded to phytochemical selective pressure. Eleven of the 12 isolates developed a 2-fold phytochemical tolerance after 30 days. The isolates contained multiple genetic mutations including mutations in a glycosyltransferase and transpeptidase gene.
The final experimental methodology explored the impact of phytochemical addition to chicken feed on the microbiome of chickens through two in vitro model experiments, and an in vivo chicken study. The studies also compared the viability of the two in vitro models as replacement for in vivo chicken experiments. Addition of both phytochemicals impacted microbiome development in all models compared to the control. Specifically increasing the levels of Escherichia-shigella and Turicibacter genera and decreasing levels of Lactobacillus pontis which may indicate an increase in disease incidence due to phytochemical supplementation.
This study shows that berberine and quercetin can act as a selective pressure for the maintenance and mutation of genes which confer antimicrobial resistance, and the selection of antimicrobial resistant isolates in isolate libraries and the chicken gastrointestinal system. Therefore, serious consideration should be given to the risks of using phytochemicals as antimicrobial replacements in both agricultural and clinical sectors.

Item Type: Thesis (Doctoral)
Subjects: QW Microbiology and Immunology > QW 4 General works. Classify here works on microbiology as a whole.
QW Microbiology and Immunology > QW 45 Microbial drug resistance. General or not elsewhere classified.
Repository link:
Item titleItem URI
Functional and Sequence-Specific Screening Protocols for the Detection of Novel Antimicrobial Resistance Genes in Metagenomic DNA
Faculty: Department: Biological Sciences > Department of Tropical Disease Biology
Depositing User: Lynn Roberts-Maloney
Date Deposited: 17 May 2023 10:15
Last Modified: 31 Dec 2023 04:12


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