Saudi Cultural Missions Theses & Dissertations
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Item Restricted Immunity and protection induced by outer membrane vesicles against Invasive non-Typhoidal Salmonella(University of Birmingham, 2024-05-24) Alshayea, Areej; Cunningham, AdamSalmonella enterica is responsible for causing both diarrheal and systemic illnesses, which remain significant global concerns. The development of vaccines that offer broad protection against multiple serovars holds potential in effectively managing diseases caused by Salmonella. Outer Membrane Vesicles (OMVs), which are naturally released by Gram-negative bacteria, show promising potential for developing subunit vaccines due to their high immunogenicity and protective effectiveness. The O-antigen of lipopolysaccharide (LPS) has been identified as a key target for inducing protective immunity. However, variation in O-antigen expression between closely related pathogens, such as S. Typhimurium and S. Enteritidis, limits cross-protection after natural infection. Modifications in the O-antigen chain length can alter outer membrane structure and composition. In this study, genetic mutations were introduced into Salmonella OMV-producing strains in order to reduce or delete LPS O-antigen expressions. The cellular, humoral, and functional immune responses to OMV from S. Typhimurium expressing wild-type length O-antigens (WT-OMV), ≤1 O-antigen repeat (wzy-OMV), or no O-antigen (wbaP-OMV) were assessed in mice immunisation studies. All OMV induced similar plasma cell and germinal centre responses, although the nature and outcomes of these responses differed. Surprisingly, wzy-OMV elicited comparable levels of anti-LPS IgG responses to WT-OMV. However, wzy-OMV and wbaP-OMV induced more robust responses against cell-surface-exposed porin proteins and cross-reactive antibodies targeting S. Enteritidis. Immunisation with wzy-OMV provided protection against S. Typhimurium comparable to that induced by WT-OMV. In contrast, after one immunisation, with any OMV type, there was minimal control of S. Enteritidis infections, except in the blood. However, after boosting with OMVs, there was an enhanced level of cross-protection.4 0Item Restricted Understanding the Dynamic Interactions between Salmonella and the Intestinal Microbiota(2023-07-19) Abdalkrim, Horeyah; Khan, AnjamSalmonella causes a broad range of diseases in humans ranging from gastroenteritis to typhoid fever. The intestinal microbiota has evolved various strategies, termed colonisation resistance, for restraining the growth of invading enteric pathogens. In addition, probiotic bacteria can strengthen the resistance of the host to invading pathogens, but our knowledge of their direct antagonistic effects on pathogens is limited. Escherichia coli Nissle 1917 is one example of a probiotic bacterium. This study aimed to identify contact-dependent and contact-independent interactions between Salmonella and selected members of the intestinal microbiota, including probiotics. This thesis used Salmonella enterica serovar Enteritidis P125109 as a model pathogen and E.coli Nissle 1917 as the probiotic strain. E.coli is the predominant member of the Gamma proteobacteria in the intestinal microbiota. In the coculture experiments, Salmonella Enteritidis and E.coli Nissle 1917 were grown together, and it was observed that the presence of both strains together did not affect their growth profiles. To explore contact-independent interactions, we utilized cell-free conditioned media from E.coli Nissle 1917. When Salmonella Enteritidis was grown in conditioned media containing molecules released by E.coli Nissle 1917, there were no significant differences in Salmonella growth compared to the control. However, an analysis of the extracellular protein profiles revealed that certain proteins involved in Salmonella's pathogenicity. Using MALDI-TOF MS, the missing proteins were identified as Salmonella pathogenicity island 1 type 3 secretion system (SPI-1 T3SS) effectors SipA and SipC. Further investigations focused on the role of indole, a signalling molecule produced by E.coli Nissle 1917, in regulating Salmonella's behaviour. We knocked out the tryptophanase gene (tnaA) in E.coli Nissle 1917, which eliminated the production of indole. RNA-sequencing analysis of Salmonella Enteritidis grown in conditioned media from either E.coli Nissle 1917 WT and the indole-deficient mutant revealed that the expression of SPI-1 T3SS genes was significantly decreased in the presence of E.coli Nissle 1917 WT and indole mutant conditioned media. Interestingly, even in the absence of indole, the expression of SPI-1 T3SS genes remained downregulated but to a lesser extent than in the presence of indole. This suggested the existence of an additional thermostable and proteinase K-resistant factor, referred to as "Factor X," which contributed significantly to the observed effects on the SPI-1 T3SS phenotype.12 0