Mycobacterium smegmatis Response to Superparamagnetic Iron Oxide Nanoparticles (SPIONs)

Motunrayo V Badejo,1,* Kudakwashe Nyambo,1,* Ephifania Geza,2 Dominic de Oliveira,3 Hleziphi V Mpundu,1 Liezel Catharine Smith,1 Michael Claeys,3 Siyabonga Ngubane,4 Craig Kinnear,1,5 Deané Basson,6 Genevéve Marx,6 Ezra Jacobus Olivier,6 Lucinda Baatjies,1 Andre G Loxton,1 Kudzanai I Tapfuma,1 Vuyo Mavumengwana1 1South African Medical Research Council Centre for Tuberculosis Research; Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town, South Africa; 2Department of Integrative Biomedical Sciences, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa; 3Department of Chemical Engineering, University of Cape Town, Cape Town, South Africa; 4Department of Chemistry, University of Cape Town, Cape Town, South Africa; 5South African Medical Research Council Genomics Platform, Cape Town, South Africa; 6Center for High Resolution Transmission Electron Microscope, Physics Department, Nelson Mandela University, Gqeberha, South Africa*These authors contributed equally to this workCorrespondence: Kudzanai I Tapfuma; Vuyo Mavumengwana, South African Medical Research Council Centre for Tuberculosis Research; Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, P.O. BOX 241, Cape Town, 8000, South Africa, Email kudzanait@sun.ac.za; vuyom@sun.ac.za; vuyo.mavu@mrc.ac.zaIntroduction: Tuberculosis, caused by Mycobacterium tuberculosis, remains a major global health challenge worsened by antimicrobial resistance. This study explores the antimycobacterial efficacy of metal-coated superparamagnetic iron oxide nanoparticles (SPIONs) as alternative therapeutic agents.Methods: SPIONs were synthesized through chemical co-precipitation and functionalized with metals to create bimetallic (Ag@SPIONs, Au@SPIONs, Cu@SPIONs, Ni@SPIONs) and trimetallic (Ag-Cu@SPIONs, Ag-Ni@SPIONs) nanoparticles. The physicochemical characteristics of the metal-coated SPIONs were assessed using microscopy and spectroscopy techniques. Antimicrobial activity of the nanoparticles against Mycobacterium smegmatis mc2 155 was evaluated using time-kill kinetic assays. Additionally, differential gene expression analysis was conducted to investigate cellular responses following nanoparticle exposure.Results: Transmission electron microscope analysis revealed average particle sizes of 10.28 nm for SPIONs, and 12.51 nm, 17.07 nm, 14.60 nm, 16.18 nm, 14.68 nm, and 15.00 nm for Ag@SPIONs, Au@SPIONs, Cu@SPIONs, Ni@SPIONs, Ag-Cu@SPIONs, and Ag-Ni@SPIONs, respectively, all displaying a predominantly spherical morphology. Antimicrobial testing demonstrated a potency ranking: Ag-Cu@SPIONs (1.95 μg/mL) > Ag-Ni@SPIONs (3.9 μg/mL) > Ag@SPIONs (3.9 μg/mL) > Cu@SPIONs (62.5 μg/mL) > Ni@SPIONs (> 62.5 μg/mL). Gene expression analysis revealed that Ag@SPIONs and Ag-Cu@SPIONs induced strong upregulation of heavy-metal detoxification genes, whereas Cu@SPIONs significantly enriched pathways linked to valine, leucine, and isoleucine degradation, and fatty acid and propanoate metabolism.Discussion: This study demonstrates that metal-coated SPIONs possess strong antimycobacterial activity and significantly modulate key metabolic and stress-response pathways in Mycobacterium smegmatis. The superior efficacy of Ag-Cu@SPIONs highlights the advantage of metal synergy in enhancing nanoparticle potency.Conclusion: Overall, the findings demonstrate that metal-coated SPIONs hold significant promise as alternative antimycobacterial agents. However, comprehensive in vivo studies are required to fully determine their therapeutic effectiveness and safety. Keywords: tuberculosis, superparamagnetic iron oxide nanoparticles, nanomedicine, antimicrobial activity, gene expressions