Effects of silver nanoparticles on microbial growth dynamics

Area of Science:

• Nanotechnology
• Microbiology
• Biotechnology

Background:

• Engineered metal nanoparticles are increasingly used in consumer products for their antimicrobial properties.
• Conventional susceptibility testing methods often lack temporal resolution, potentially misrepresenting nanoparticle effects.
• A need exists for dynamic assays to evaluate nanoparticle interactions with microorganisms.

Purpose of the Study:

• To establish and adapt a 96-well format cultivation-based assay for time-resolved testing of nanoparticle effects on microorganisms.
• To evaluate the dynamic antimicrobial effects of spherical silver (Ag(0)) nanoparticles on Cupriavidus necator H16.

Main Methods:

• Developed a modified, automated, high-throughput assay for simultaneous cultivation and on-line analysis of microbial growth inhibition.
• Applied the assay to Cupriavidus necator H16 using spherical silver (Ag(0)) nanoparticles (primary particle size D90 < 15 nm).
• Investigated the effects of varying Ag(0) concentrations and addition times during microbial growth stages.

Main Results:

• Ag(0) concentrations above 80 μg ml⁻¹ caused complete and irreversible growth inhibition.
• Concentrations between 20 and 80 μg ml⁻¹ led to extended lag phases and partial growth inhibition.
• Addition of Ag(0) nanoparticles at early growth stages (0–6 h) resulted in complete inhibition, while later addition (≥9 h) allowed full recovery.

Conclusions:

• Contrary to expectations, certain Ag(0) nanoparticle concentrations stimulated C. necator growth.
• Microbial susceptibility to Ag(0) nanoparticles varied significantly depending on the organism's growth stage.
• Time-resolved analysis is crucial for accurately assessing the dynamic effects of nanoparticles on microbial growth.