Saudi Cultural Missions Theses & Dissertations
Permanent URI for this communityhttps://drepo.sdl.edu.sa/handle/20.500.14154/10
Browse
3 results
Search Results
Item 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 Precious metal recovery using biotechnological approaches: Biosynthesis of functional nanomaterials(The University of Manchester, 2024) Alkhammali, Sultan A; Lloyd, Jonathan; O’Driscoll, Brian; Coker, VictoriaGold mining industries generate significant residues e.g., aqueous waste, waste rock, and tailings, potentially containing unrecovered gold, heavy metals, and toxic substances. Therefore, this thesis explores the mineralogy and geochemistry of solid tailings from two Saudi gold mines, investigating the potential use of Geobacter sulfurreducens for bioprocessing PMs in both lab-synthesised solutions and mineral processing solutions from Sukhaybarat Mine, Saudi Arabia. Quartz, albite, micas, sulphide, and clay minerals were commonly found in tailings from Sukhaybarat and Mahd Adh Dhahab Mines. The presence of heavy metals suggested their association with sulphide minerals. Low concentrations of Au and Ag were detected, except for a notably high Au concentration (>25 ppm) in the Sukhaybarat sample. The preventive measures implemented help reduce the possibility of the surrounding areas being adversely affected. Bioreduction experiments were conducted in synthetic systems for Au(III) and Ag(I), both individually and as bimetallic compounds. The results showed the high efficiency of G. sulfurreducens in reducing Au(III) and Ag(I) to nano-scale zero-valent metal precipitates, with H₂ proving to be a significantly more efficient electron donor, achieving removal rates (>90%) for Au(III) and Ag(I) compared to sodium acetate. XRD confirmed the presence of Au(0) and Ag(0) NPs, particularly in monometallic samples with H2 and cells. TEM showed differences in NPs sizes and distributions on bacterial cells between H2 and sodium acetate systems. XPS was also used to identify Au species and assess the extent of Au(III) reduction by G. sulfurreducens using sodium acetate. The fitted XPS data suggested the presence of mainly Au(0) and a minor portion of Au(I). In mineral processing solutions, G. sulfurreducens and H2 showed efficient removal of dissolved Au and Ag, reaching >90%. TEM showed Au and Ag nanoparticles adhering to the surface of bacterial cells, ranging in size from 5 to 10 nm. The alkaline pH (9.1) of these solutions could be a contributing factor to the observed small size of NPs. This study presents a novel biorecovery approach using G. sulfurreducens, showing its efficacy in removing dissolved Au and Ag, especially from cyanide-containing solutions, highlighting its potential as a promising candidate for precious metal recovery in the mining sector, including mining effluents. These findings contribute to the development of sustainable mining practices, aligning with global efforts toward eco-friendly resource exploitation.33 0Item Restricted The Effectiveness of Silver Diamine Fluoride (SDF) on Caries Lesions in Adults: retrospective study evaluating the longevity of SDF treated teeth in adult patients using a dental school data record(2025) Al Saffer, Ala; Kolker, JustineSilver diamine fluoride (SDF) is used to treat dental caries lesions on primary teeth in children and have been found effective. Adults may also benefit from the use of SDF in treating exposed initial root caries lesions, yet such studies are lacking. The aim of this retrospective study was to determine the factors related to longevity of adult patients’ teeth after SDF treatment. Methods: Data from the University of Iowa College of Dentistry data base (AxiUm) were used for this study. Patients aged 18 years and older with one or more code D1354 between 2016 and 2021 were included. Patient variables included: age, gender, race, number of medications, smoking status, insurance status, and number of D1354 codes overall. Tooth variables included: tooth number, number of D1354 codes applied on the tooth, and subsequent treatment (restoration, root canal treatment, extraction). Operator variables included: provider type (student, post-grad, faculty) and type of clinic (geriatric vs. other). The dependent outcome variable was survival defined as not needing subsequent treatment. Statistical software was used to calculate chi-square values used for analyses to determine relationship between variables and survival. Results: Results included 1772 patients with 2985 SDF treated teeth. Patients that had significantly higher failure (p <.001 to <.05) with tobacco use. Teeth with crowns prior to SDF treatment had higher chance of failure. Multiple applications of SDF had higher chances of not failing.32 0