Mycobacterium smegmatis Response to Superparamagnetic Iron Oxide Nanoparticles (SPIONs)

Introduction: 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 mc 2 155 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