Ntuli, Phindile Lindiwe2024-10-212024-10-212023-10Ntuli, Phindile Lindiwe. (2023). Investigating the susceptibility of Enterobacter xiangfangensis Pb204 to various silver(I) phosphine compounds and identifying the molecular basis of resistance though comparative genomics. [Master's dissertation, University of the Witwatersrand, Johannesburg].https://hdl.handle.net/10539/41763A dissertation submitted in fulfilment of the requirements for the degree Master of Science (Molecular and Cell Biology) to the Faculty of Science, School of Molecular and Cell Biology, University of the Witwatersrand, Johannesburg, 2023.In developing countries, the endemic of nosocomial infections is notably high, particularly in the ICU settings and neonatal infections, where it accounts for a prevalence of 15.5% with an increased mortality rate. ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter species) pathogens are highly virulent and resistant microbes that predominantly causes nosocomial infections in clinical settings. These pathogens adhere to the surface of hospital equipment and form biofilms, thereby increasing the susceptibility of patients to acquiring such infections during extended hospital stays. Recent studies have shown that Enterobacter xiangfangensis is the main clinical culprit in the Enterobacter cloacae complex, thus making it the main therapeutic target among the ESKAPE pathogens. This study evaluated the antimicrobial properties of various silver(I) phosphine compounds on E. xiangfangensis Pb204 and E. xiangfangensis LMG 27195T. The minimum inhibitory concentration (MIC) assay was done, though the microdilution technique coupled with iodonitrotetrazolium chloride (INT) dye. The antibiofilm activity of the silver(I) phosphine compounds on biofilm formation and degradation were evaluated using the crystal violet assay, and the metabolic activity of cells in biofilms was assessed using the XTT assay. Additionally, the molecular mechanism of silver resistance was investigated by measuring gene expression of E. xiangfangensis Pb204 cells when treated with the silver(I) phosphine compound UJ1, silver nitrate and silver sulfadiazine using RT-qPCR. The MIC of the silver(I) phosphine compounds was 0.125 mg/ml for both E. xiangfangensis Pb204 and E. xiangfangensis LMG 27195T. Moreover, the compound UJ1 showed a bactericidal effect against E. xiangfangensis LMG 27195𝑇. Furthermore, the silver(I) phosphine compounds have antibiofilm activity since they inhibit biofilm formation, disrupt matured biofilms, and reduce metabolic activity in E. xiangfangensis Pb204 and E. xiangfangensis LMG 27195T biofilms. The resistance in E. xiangfangensis Pb204 strain is due to the upregulation of the silver resistance pathway encoded on the integrative and conjugative element (ICE) element. Core and unique protein coding genes between E. xiangfangensis Pb204 and E. xiangfangensis LMG 27195T were identified though comparative genomics. Functional annotation of core and unique protein revealed that E. xiangfangensis Pb204 evolved to gain genetic material coding for inorganic ion transport and carbohydrate transport metabolism. Knowledge of these can be used in future studies in the utilization of silver metals as antimicrobial agents.en©2023 University of the Witwatersrand, Johannesburg. All rights reserved. The copyright in this work vests in the University of the Witwatersrand, Johannesburg. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of University of the Witwatersrand, Johannesburg.ESKAPEEnterobacter XiangfangensisSilver(I) phosphine compoundsSilver resistanceMetal-based antimicrobialsUCTDSDG-3: Good health and well-beingDissertationUniversity of the Witwatersrand, Johannesburg