Antibacterial and Antibiofilm Activities of Streptomyces rochei-Mediated Zinc Oxide Nanoparticles against Dental Caries-Causing Streptococcus mutans - An In Vitro Study

INTRODUCTION: Bacterial biofilms in the oral cavity lead to dental decay and reduce the durability of dental restorations. In this context, microbe-derived nanomaterials offer promising, broad-spectrum alternatives to synthetic drugs. This study aims to biosynthesize eco-friendly zinc oxide nanoparticles (ZnONPs) by a marine actinobacterium Streptomyces rochei and further characterize and ascertain its antibacterial and antibiofilm activities against the oral pathogen Streptococcus mutans. MATERIALS AND METHODS: ZnONPs were synthesised using S. rochei and characterised through spectroscopical analysis. Antibacterial activity was assessed using well-diffusion and multi-well plate assays. Biofilm inhibitory activity was determined using crystal violet assay and validated by microscopy. RESULTS: ZnONPs showed Ultraviolet - Visible Spectroscopy (UV-Vis) peaks at 364 nm. Fourier Transform - Infrared Spectroscopy (FT-IR) results revealed the interaction of possible functional groups associated with the stability and surface chemistry of the nanoparticle. Field Emission - Scanning Electron Microscope (FE-SEM) results showed the morphology of ZnONPs was irregular and flaky, with an average grain size of 55.04 nm. ZnONPs exhibited profound antibacterial activity (Halo: 17.9 mm) with minimal bacteriostatic (50 μg/ml) and bactericidal (100 μg/ml) values. Biofilm inhibitory effect of ZnONPs inferred a substantial (P < 0.05) reduction in a dose-dependent manner against S. mutans (24%-96%). Crystal violet and Confocal Laser Scanning Microscopic (CLSM) visuals manifested the distorted biofilm architecture of S. mutans. CONCLUSION: This novel approach underscores a sustainable method for synthesising ZnONPs and suggests that it could be effectively used as nano-antibiotics by coating the surface of dental implants.