Saudi Cultural Missions Theses & Dissertations
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Item Restricted Oral biofilm and host-pathogen models: a semi- systematic review and future perspectives(University Of Glasgow, 2024-08) Alshehri, Khalid; Brown, JasonAbstract Introduction: Oral biofilms, complex microbial communities found on various surfaces within the oral cavity, play a critical role in the development and progression of oral diseases such as dental caries, periodontal diseases, and mucosal infections. Understanding the formation, structure, and pathogenicity of these biofilms is essential for improving prevention and treatment strategies. Aims: This review aims to evaluate recent advancements in the development and application of in vitro multi-species oral biofilm models, with a focus on studies published between January 2019 and July 2024. The review seeks to identify gaps in current research and suggest future directions for enhancing the physiological relevance of these models. Methods: A systematic literature search was conducted in the PubMed database, following PRISMA guidelines. Studies were selected based on predefined inclusion and exclusion criteria, focusing on multi-species biofilm models in vitro. The review analyzed methodologies, findings, and limitations of the selected studies. Findings: The review identified six key studies employing various in vitro models, ranging from continuous flow systems to static models. These studies highlighted the importance of specific microbial interactions, biofilm maturation processes, and the impact of different substrates on biofilm formation. However, limitations were noted in replicating the complexity of the in vivo oral environment, particularly in capturing the dynamic conditions and microbial diversity. Discussion: While significant progress has been made in the development of in vitro biofilm models, challenges remain in creating systems that accurately mimic the oral microenvironment. Advances in microfluidic devices and 'OMICs' technologies offer promising avenues for future research. Additionally, there is a need for long-term studies that better reflect the chronic nature of biofilm-related infections. Conclusion: The development of in vitro models that closely replicate the in vivo conditions of the oral cavity is crucial for advancing our understanding of oral biofilms and their role in disease progression. Future research should focus on integrating advanced technologies and improving model complexity to enhance the predictive value of these systems for clinical applications.14 0Item Restricted Understanding the effect of silver exposure on P. aeruginosa biofilms(The University of Manchester, 2025) Almuzaini, Osama; Humphreys, Gavin; Mcbain , AndrewBackground. The longstanding belief of the rarity of silver resistance development has facilitated the widespread use of silver in wound dressings. However, studies have shown that the prolonged exposure of clinical samples under laboratory investigation can result in reduced silver susceptibility. Most of these prolonged exposures have been conducted on planktonic isolates, whereas biofilms are the predominant state in chronic wounds. This PhD thesis aims to assess the bacteriological effects of repeated passaging of bacterial biofilm to ionic silver. Methods. Monospecies biofilms of Pseudomonas aeruginosa (WIBG 2.2) were grown in MBEC devices and repeatedly passaged under two distinct silver nitrate concentrations setting: (i) a constant ionic silver concentration and (ii) dynamic concentrations, where the exposure concentration was determined before each passage. After the fifth passage, biofilm variants were extracted, cultured on agar and compared morphologically. New morphological variants were limited to biofilms exposed to dynamic concentrations. MICs and MBECs were performed to assess the silver sensitivity of these variants, as well as cross-resistance to antimicrobials utilizing the EUCAST zone of inhibition protocol. Biofilm biomass of P. aeruginosa silver-treated variants grown in an MBEC device was determined using crystal violet staining. Extracellular DNA (eDNA) within the biofilm was visualized and quantified utilizing confocal laser scanning microscopy. eDNA was further digested by Deoxyribonuclease-I to evaluate its role in silver recalcitrance and biofilm integrity. Given the generation of mucoid biofilm, alginate production was measured using a carbazole assay. Following the phenotypic changes, all variants underwent whole genome sequencing to detect associated mutations. Bacterial competitive fitness was assessed using a broth co-culture assay, and bacterial-host virulence was determined using Galleria mellonella survival model. Finally, the morphological changes of the biofilm-derived variants were monitored through planktonic passaging in the absence of silver exposure, with growth kinetics determined using a plate reader. Results. Following dynamic exposure to ionic silver, mucoid biofilms were generated after the fifth passage, exhibiting distinct colony morphology named SV, BV, and BWV. Control biofilms passaged in LB broth resulted in two distinct colony morphologies named SC and BC. The treated biofilm variants (SV and BV) and one of the control variants (SC) exhibited reduced colony morphology. SV and BV showed the highest MBEC values, 2227- fold greater than the parent strain and 32-fold greater than the control passage. Compared to the baseline (P0), SV and SC exhibited a highly significant increase in biofilm biomass (P<0.0001), while BV, BWV, and BC exhibited no significant changes. Increased eDNA disposition was observed exclusively within the SV biofilm architecture. Alginate production was highest in BV, followed by BWV and SV, while control biofilm variants (SC and BC) exhibited no significant increases compared to the parent strain. Silver sensitivity was restored by treating biofilms with DNAse I, although this treatment also significantly reduced the biofilm biomass. None of the bacterial variants showed altered virulence compared to the parent strain, although BV exhibited a reduced growth rate. Both SV and BV demonstrated higher competitive fitness than the parent strain. The adapted colony morphology was transient upon subsequent planktonic passage in the absence of ionic silver. SV's colony morphology remained stable until the 11th passage, after which it started to resemble the parent strain. Similarly, BV reverted to the parent morphology by the 10th passage, and BWV began reverting by the 5th passage. In controls, BC began reverting by the 3rd passage, while SC started reverting by the 9th passage. Conclusion: Silver-adapted strains gained resistance through various mechanisms within their sessile phenotype embedded in the complex and heterogenous biofilm ecosystem, including eDNA deposition and alginate production, accompanied by several mutations. These mutations were associated with transport activity, virulence, metabolism, transcription and regulatory functions.12 0Item Restricted Effect of Dextranase on S. mutans Biofilms(Univeristy of Michgian, 2024) Almalki, Jawharah; Tenuta, Livia MDental biofilms are complex structures that are influenced by their environments. Dysbiosis of these biofilms can cause diseases, with dental caries being the most prevalent biofilm-mediated disease. This dissertation investigates the composition of biofilms, their role in dental caries, and the concept of biofilm alteration and modification by the use of enzymatic treatments. A special focus is given to the extracellular polysaccharides in the dental biofilm matrix, which are formed upon exposure to sucrose. In a review manuscript, we discuss the existing knowledge of biofilm modification with an extensive review of the literature. Over the last decades, different enzymes have been used in an attempt to modify the biofilm matrix and make it more susceptible to anticaries treatments. Dextranase, mutanase, and eDNAse are example of enzymes which show promising results for continuing investigation. Then, we experimentally tested in vitro the effect of short (1 min) treatments, twice/day, on the composition of cariogenic Streptococcus mutans biofilms grown in the presence of sucrose. Dextranase at 2 and 20 units/mL were able to significantly reduce biofilm biomass; the proportion of extracellular polysaccharides to total biofilm mass was not significantly different between treatments with or without dextranase. In conclusion, enzymes that modify the biofilm matrix can be adjunct agents in anticaries treatments; for example, the use of dextranase was shown to reduce S. mutans biofilm mass and potentially its cariogenicity.35 0Item Restricted Evaluating the Efficacy of Laser-Assisted Endodontic Treatment: Insights from In Vitro Models and In Vivo Studies(University of Pennsylvania, 2024-08) Mominkhan, Dana; Teles, FlaviaObjective: To develop a clinically relevant complex multi-species biofilm model of endodontic infection and evaluate the performance of new laser technologies in vitro and in vivo. Methods: For the in vitro studies, bacterial species were selected based on the literature and the correlation network analysis (CNA) of our collection of 206 root canal samples. Biofilms were developed for 7 and 14 days. Three tooth models (SM, DMK, SMS) were compared using 200 extracted human premolars and four different laser technologies were tested. For the in vivo studies, patients presenting apical periodontitis were selected for treatment using the standard of care (NaOCl, control) or adjunctive laser treatment (test). Outcomes measured included CFU reduction and pain assessment. Results were evaluated using culture, SEM, FISH and CLSM LIVE/DEAD analysis. Data were analyzed using Kruskal-Wallis, PCA and GEE. Results: Tooth models were assessed with E. faecalis biofilms and tested using a multi-species biofilm composed of A. viscosus, F. nucleatum, P. micra, P. nigrescens and S. sanguinis. DMK was the most effective tooth model. EdgePRO™ was the most effective laser in the presence of NaOCl and LEAP™ in its absence. Fifty-two patients completed the study. CFUs were reduced by both treatments. No differences were observed regarding post-operative pain. Conclusion: The new multi-species biofilm mode developed here is a clinically relevant and effective tool to assess new treatments. EdgePRO™ is effective in reducing CFUs of in vitro and in vivo biofilms.25 0Item Restricted Adhesion and biofilm formation of Streptococcus pneumoniae(University of Liverpool, 2024-07-01) Albalawi, Malaak; Neill, Daniel; Kadioglu, ArasThe pneumococcus is a commensal bacterium of the human respiratory tract, but it can invade the sterile sites of the host, causing sometimes lethal disease. The aim of this study was to investigate factors that contribute to the cellular adhesion and invasion potential of S. pneumoniae at the early stages of infection, in both nasopharyngeal carriage and invasive disease. Phenotypic profiling of representative isolates of 15 pneumococcal serotypes of clinical relevance was undertaken, to understand the range of adhesion potentials of the pneumococcus to A549 airway epithelial cells. In parallel, phenotypic profiling of 20 closely related pneumococcal lineages from a previous experimental evolution study was performed. All pneumococcal strains were able to adhere to A549 cells but intracellular invasion was a rare event. The adhesion and invasion potential of strains was affected by capsule type and capsular thickness and by the production of the cholesterol-dependent cytolytic toxin pneumolysin. The ability to form biofilms is key to pneumococcal colonisation, which is itself a key step in the progression towards pneumococcal diseases. A positive correlation was observed between the ability of clinical strains to form biofilms and their adhesion potential. Pneumococcal proteins contributing to biofilm lifestyles were identified using M/S comparison of pneumococci during biofilm and planktonic growth. This was undertaken with strains identified as strong biofilm formers, and included serotypes 7F and 19A and two serotype 2 D39-derived strains from a previous experimental evolution study. The abundance of a set of functionally related proteins was increased during biofilm growth, relative to in planktonic cultures. Data showed that pneumococci in biofilms are likely virulence-attenuated compared to planktonic pneumococci, due to decreased production of virulence proteins such as HtrA and pneumolysin (Ply). The upregulated proteins in biofilm samples were those associated with adhesion such as LytC and PsaA, whilst those associated with virulence and toxicity were less abundant in biofilms samples. Collectively, this study highlights the diverse phenotypes that contribute to the adhesion potential of pneumococci. Furthermore, it identifies proteins that are markedly upregulated in biofilms. Such factors might be attractive targets for future therapeutic interventions.11 0Item Restricted The effect of components of electrospun material on S. aureus, P. aeruginosa and E. coli bacterial growth and biofilm formation(Saudi Digital Library, 2023-11-28) Alomair, Munirah; Powell, LydiaThe prevalence of chronic wounds in immunocompromised patients has risen recently, leading to increased morbidity and mortality rates. The emergence of antibiotic resistance has necessitated novel technology for the treatment of these wounds. In order to provide a bespoke wound dressing for patients, Corryn Biotechnologies is developing an innovative device that electrospins a polymer solution directly onto a wound. The antibiotic activity of the electrospun components, namely dimethyl sulfoxide (DMSO), collagen 1, acetone and a non-disclosed polymer solution, were tested against gram-positive methicillin-resistant Staphylococcus aureus (MRSA 1004A) and gram-negative Pseudomonas aeruginosa PAO1 and Escherichia coli IR57 in both planktonic and biofilm assays to determine their effect on bacterial growth and biofilm formation. Minimum inhibitory concentration (MIC) assays were used to evaluate the effect of DMSO against MRSA 1004A, P. aeruginosa PAO1, and E. coli IR57, with resultant MICs of 25%, 6.25%, and 12.5%, respectively. The MICs of collagen 1 and acetone were >50% for both gram-positive and gram-negative bacteria. Confocal laser scanning microscopy (CLSM) revealed that DMSO significant inhibited the formation of MRSA 1004A biofilm biomass at both concentrations of 1/2 MIC DMSO (p<0.0001) and 1/4 MIC DMSO (p=0.0017), with increased cell death achieved with 1/2 MIC DMSO treatment (p=0.0003). The MRSA 1004A biofilm roughness significantly increased with 1/2 MIC DMSO (p=0.0008), but the average thickness area and average thickness biomass were significantly decreased (both p<0.0001) at 1/2 MIC DMSO treatment. The P. aeruginosa PAO1 biofilm biomass significantly increased with 1/2 MIC DMSO treatment (p=0.03), while cellular death decreased with 1/4 MIC DMSO treatment (p=0.038). The effects of the components of the electrospun solution against the most common strains of gram-positive and gram-negative bacteria in chronic wounds highlight the potential application of these components to form a bespoke wound dressing to reduce biofilm formation and aid in chronic wound healing.12 0