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The Use of Metal Ions and Graphene-Based Compounds as Novel Antimicrobials Against Multidrug Resistant Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus

Karaky, Nathalie (2020) The Use of Metal Ions and Graphene-Based Compounds as Novel Antimicrobials Against Multidrug Resistant Pseudomonas aeruginosa, Klebsiella pneumoniae and Staphylococcus aureus. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

The burden of antimicrobial resistance is a daily challenge in clinical settings, especially in intensive care units. The escalating trends of multidrug-resistant (MDR) bacteria are reported on a global scale today, and the loss of effective antibiotics and disinfectants undermines the ability to fight infectious diseases. The development of novel antibacterial agents is urgently needed in healthcare settings to reduce bacterial resistance and potential nosocomial infections. This study aimed at assessing the antimicrobial effect of metal ions and graphene-based compounds against multidrug resistant (MDR) isolates of Pseudomonas aeruginosa, Staphylococcus aureus and Klebsiella pneumoniae. It also aimed at incorporating the successful combinations of metal ions and graphene composites into novel formulations of skin cleansers and nasal sprays/ointments that are effective against MDR chlorhexidine-adapted K. pneumoniae and mupirocin-resistant S. aureus in clinical settings. The antimicrobial efficacy of eighteen metal ion solutions, graphene and graphene oxide were tested, individually and in combination, against ten clinical isolates of Pseudomonas aeruginosa, Staphylococcus aureus and Klebsiella pneumoniae using minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). The antibiofilm activity of the compounds was tested using crystal violet biofilm assays (CVBA) and XTT assays. The synergistic effect between metal ions or combinations showing the best inhibitory activity against the three bacterial species and the excipients of the skin cleanser or nasal spray/ointment was assessed using fractional inhibitory concentration (FIC). Compounds that did not show any antagonistic effect were tested for their cytotoxicity using MTS assay against human skin fibroblast cell line, and were incorporated into different formulations of skin disinfectant, and nasal spray/ointment. The antimicrobial efficacy of the formulations was tested using the agar well diffusion method and CVBA assay. The organoleptic characteristics, uniformity, spreadability, thermal stability and other physical characteristics of each formulation were also evaluated. Morphological changes in bacterial xvi cells treated with the tested formulations were visualized using scanning electron microscopy (SEM). Results showed that platinum, palladium, gold, tin and molybdenum ions exhibited the best inhibitory effect against the planktonic cells of P. aeruginosa, S. aureus and K. pneumoniae. Graphene oxide demonstrated no antimicrobial effect (>500 mg/L) against the 10 isolates, whilst graphene showed an excellent against S. aureus and K. pneumoniae only. It was evident, however, that the addition of graphene or graphene oxide enhanced the antimicrobial effect of metal ions against the three bacterial species. Cytotoxicity readings revealed that gallium, indium, platinum, palladium, gold, graphene and graphene oxide were not toxic to the tested skin fibroblasts. Various formulations of skin disinfectants (14), topical ointments (9) and nasal sprays (9) containing metal ions and graphene composites were tested. The best inhibitory and antibiofilm activities were revealed by formulations containing gold/graphene, gold, platinum, platinum/graphene and palladium. The antibacterial effect of the different tested formulations was further confirmed by the clear morphological damages shown in bacterial cells characterized by the formation of deep grooves, pores, or cuts in their cell walls. In the light of the inefficacy of the currently used antibiotics and disinfectants, this study highlighted specific metal ions, used alone or in combination with graphene composites, owing their antibacterial activity, as promising potential novel antibacterial agents in clinical settings.

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