Abstract

IntroductionAntimicrobial resistance is a global health crisis due to the emergence and spread of multidrug-resistant bacteria, driven by poor antibiotic stewardship, particularly in low to middle income countries where antibiotics can be bought over the counter. Currently, the molecular diagnosis of infections and genomic DNA extraction are both hindered by several factors including, expense, time, technical expertise, and the requirement of a laboratory-based setting. This makes it difficult to extract genomic material at point-of-care preventing the use of rapid molecular methods for the detection of antibiotic resistant genes. Thus, the gold standard for determining the appropriate antibiotics to treat infections requires culture-based methods that are time consuming and laborious. MethodsIn this project a novel methodology was developed using the Swift® portable SYSTEM 8 GHz microwave to investigate the effectiveness of extracting DNA as well as the molecular effects of microwave irradiation upon both sensitive and antibiotic-resistant pathogens.Extraction of DNA was optimised on a strain of E. coli and S. aureus to determine two different Gram-negative and Gram-positive microwave regimes by measuring the release of single-stranded DNA (ssDNA) using the Qubit® ssDNA Assay Kit. The chosen microwave regimes were then tested on four strains of E. coli, K. pneumoniae and S. aureus comprised of both antibiotic resistant and sensitive phenotypes. Bacterial cell viability was measured post-exposure and the concentration of both ss- and double-stranded DNA (dsDNA) (Qubit® dsDNA Broad Range Assay Kit) was quantified, while the molecular effects of microwaves were explored by visualising DNA fragment patterns and amplifying the 16S rRNA gene using PCR. The mechanisms by which 8 GHz microwaves extract DNA was explored by looking at the effect of ionic strength on sample heating, while cell flow cytometry and scanning electron microscopy was used to explore the effects of microwaves on the ultrastructure of bacteria.ResultsOptimisation, based on the release of ssDNA, resulted in the selection of two different microwave regimes for both Gram-types. Gram-positive bacteria required longer exposure times due to lower quantities of ssDNA being released compared to Gram-negative bacteria. Generally, microwaves were more effective at extracting DNA from Gram-negative bacteria, particularly Klebsiella pneumoniae, compared to Gram-positive bacteria. Microwaves at 8 GHz greatly reduced viable counts in both Gram-types regardless of the microwave Regime employed. For all strains, DNA quantification showed greater concentrations of ssDNA being released compared to dsDNA. DNA fragmentation patterns were similar between E. coli and K. pneumoniae for both microwave regimes and for the non-microwaved control, while little to no fragmentation was seen for S. aureus. For all strains the 16S rRNA gene was successfully amplified post-microwave exposure using PCR. Dipolar polarisation was shown to be the main mechanism responsible for dielectric heating when using 8 GHz microwaves. No significant difference was shown in the inactivation, release of DNA, or uptake of propidium iodide in bacteria when comparing between conventional and microwave heating, sub-lethal and lethal heating alike. Scanning electron microscopy revealed clear signs of damage to the surface structure of Gram-negative bacteria subjected to lethal conventional heating, whereas no comparable surface damage was observed following lethal microwave treatment.

Awarding Institution(s)

University of Plymouth

Supervisor

Tina Joshi, Mathew Upton, Matthew Kidd, Vehid Salih

Document Type

Thesis

Publication Date

2026

Embargo Period

2026-06-28

Deposit Date

June 2026

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

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