Antibacterial Efficacy and Proteomic Response of Silver Nanoparticles in Escherichia coli XL1-Red

Klepetsanis Pavlos ^1*

This study determined AgNP antibacterial efficacy, resistance mechanisms in E. coli mutants, and impact of particle aggregation on nanoparticle performance.

Abstract

Background: Silver nanoparticles (AgNPs) are well-known for their antibacterial properties, which have prompted their use in various applications. Understanding the bacterial response to AgNPs is crucial for optimizing their effectiveness and overcoming resistance. Methods: AgNPs were synthesized through the borohydride reduction of silver nitrate (AgNO3) and characterized using dynamic light scattering (DLS) to measure their dimensions. The AgNPs were applied to the XL1-Red mutator strain of Escherichia coli to study proteomic changes between Ag-resistant mutants and non-AgNP-treated mutants. Ag-resistant mutants were identified by their ability to survive repeated exposures to AgNPs. Proteomic analysis focused on outer membrane proteins (OmpC, OmpF), and UV exposure was used to induce and study AgNP aggregation. Results: The treatment with AgNPs resulted in a significant reduction in colony numbers, demonstrating their antibacterial effect. Surviving colonies were able to adapt to AgNP exposure, as evidenced by their survival in repeated treatments. Proteomic analysis showed a decrease in the expression of outer membrane proteins (OmpC, OmpF) in Ag-resistant mutants compared to non-AgNP-treated samples. Additionally, UV exposure caused AgNP aggregation, as indicated by a color change and a shift in the Surface Plasmon Resonance (SPR) peak. Aggregated AgNPs displayed reduced antibacterial efficacy compared to non-aggregated AgNPs. Conclusion: This study underscores the potential of AgNPs for antibacterial applications and reveals bacterial adaptation mechanisms to AgNP exposure. The findings suggest that optimizing AgNP characteristics, such as preventing aggregation, could enhance their antibacterial effectiveness.

Keywords: Silver nanoparticles, antibacterial resistance, outer membrane proteins, E. coli XL1-Red, nanoparticle aggregation

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