Chitosan-based antibiofilm strategies and microbial profiling of endodontic infections

Shaban, Suror Mohamad Ahmad (2026) Chitosan-based antibiofilm strategies and microbial profiling of endodontic infections. PhD thesis, University of Glasgow.

Abstract

Persistent endodontic infections remain a clinical challenge, with a subset of cases failing to respond to current treatment strategies. These failures are increasingly attributed to the complexity of endodontic biofilms, the presence of microbial biofilms and limitations in our understanding of the endodontic microbiome. The aims of this thesis were twofold: first, to evaluate the antimicrobial and antibiofilm activity of a modified chitosan polymer, chitosan hydrochloride, against Candida albicans; and second, to comprehensively review and reanalyse published endodontic microbiome studies employing 16S rRNA gene sequencing.

A subset of clinical C. albicans isolates, alongside reference strains were screen for biofilm-forming ability and susceptibility to medium- and low-molecularweight chitosan. The investigations demonstrated that C. albicans displays marked inter-strain variability in biofilm formation, metabolic activity, and susceptibility to chitosan-based treatments, with modestly enhanced antifungal activity associated with low-molecular-weight chitosan. The chitosan derivative CS3H, generated through chemical modification of low-molecular-weight chitosan, exhibited concentration-dependent antifungal activity and was more effective than commercial chitosan, particularly against planktonic cells. In addition, CS3H significantly inhibited C. albicans adhesion and demonstrated pronounced antibiofilm activity.

Transcriptomic analysis revealed that exposure to the CS3H polymer affected multiple cellular pathways, including upregulation of genes associated with cell wall and membrane integrity, and downregulation of genes involved in zinc homeostasis. Zinc supplementation partially restored the metabolic activity of CS3H-treated biofilms, further supporting the role of zinc homeostasis disruption in the mechanism of action of CS3H. C. albicans GSK067 clinical isolate consistently showed lower susceptibility to CS3H than other isolates and its six-hour biofilms showed higher expression of chitinase gene CHT3 compared with a more susceptible clinical isolate (GSK049). Consistent with these findings, C. albicans GSK067 exhibited increased chitinase activity, and the addition of exogenous chitinase further enhanced resistance, suggesting a potential mechanism underlying reduced treatment efficacy.

Following the treatment investigations, a secondary aim was to review endodontic microbiome studies, which identified substantial heterogeneity in methodological and technical parameters, including sampling strategies, DNA extraction protocols and sequencing approaches. Reanalysis of available raw sequencing data confirmed that endodontic infections are highly diverse microbial ecosystems with marked variability in taxon abundance. Despite this variability, overall community composition was broadly similar across clinical contexts, supporting the presence of shared core microbiome. Notably, Enterococcus species, including E. faecalis and E. casseliflavus, were enriched in post-treatment infections. No significant differences in diversity were observed between symptomatic and asymptomatic cases; however, the relative abundances of several taxa varied according to infection type, symptomology, and sampling site and approach.

Chitosan demonstrated promising antifungal activity against most of the tested C. albicans isolates; however, the efficacy of CS3H derivative remains to be confirmed against complex multispecies biofilms and the potential influence of fungal and human chitinases on its activity requires further investigation. These findings underscore the limitations of cross-study comparisons and highlight the need for standardised methodologies. Primary infections showed greater microbial diversity than post-treatment infections, while Enterococcus species were enriched after treatment. These findings provide insights into biofilm-associated infections and support the development of improved in vitro models and therapeutic strategies. Despite extensive efforts to characterise the endodontic microbiome, many aspects of its composition, function and clinical relevance remain unresolved. Future investigations integrating host–microbe interactions, non-bacterial microbial communities (including fungi and archaea) and functional analyses will be essential to achieve a more comprehensive understanding of endodontic infection pathogenesis and to inform improved clinical management strategies.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from the Libyan Embassy and the Ministry of Higher Education and Research.
• Subjects: R Medicine > RK Dentistry
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Medicine, Dentistry & Nursing > Dental School
• Supervisor's Name: McLean, Professor William and Delaney, Dr. Christopher
• Date of Award: 2026
• Depositing User: Theses Team
• Unique ID: glathesis:2026-85989
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 02 Jun 2026 14:29
• Last Modified: 02 Jun 2026 14:29
• Thesis DOI: 10.5525/gla.thesis.85989
• URI: https://theses.gla.ac.uk/id/eprint/85989