Evaluation of antimicrobial potential of free gallic acid and its polyvinyl-based nano-formulation

This study explores the antimicrobial potential of gallic acid (GA) and gallic acid loaded with polyvinyl alcohol (PVA) nanocarriers as a good source of phenolic acids against various gram-positive bacteria including Staphylococcus aureus and Streptococcus mutans and gram-negative bacteria such as Escherichia coli and Salmonella typhi, as well as a fungal species (Candida albicans). Prior to evaluating their antimicrobial activity, the physical characterization of the GA-PVA-NPs was carried out using different techniques such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and dynamic light scattering (DLS). TEM imaging revealed nanoparticles with a uniform size and morphology, while DLS analysis confirmed the presence of nanoparticles with an average size of 128.1 ± 31.9 nm, indicating their potential for improved interaction with microbial cells. It is well established that nanoparticles around 100-150 nm can more easily penetrate bacterial cell walls, leading to membrane damage, oxidative stress through reactive oxygen species (ROS) generation, and disruption of vital cellular functions such as protein synthesis and DNA replication. These size-dependent mechanisms play a key role in enhancing the antimicrobial properties of nanoparticles. Following characterization, antimicrobial activity was assessed using the well diffusion technique and microplate reader assay. The microplate reader assay provided quantitative data, showing that gallic acid exhibited the highest inhibition against S. aureus (97.77%) and S. typhi (88.22%), while GA-PVA-NPs also demonstrated significant antimicrobial effects. The well diffusion technique confirmed these results, with inhibition zones ranging from 17.33 mm to 33.00 mm. The reduced effectiveness of the nanoparticles at lower concentrations may not necessarily undermine their potential, as the increased stability and controlled release properties of nanoparticles could provide long-term antimicrobial action that is beneficial for specific applications. These findings suggest that GA-PVA-NPs have significant potential as antimicrobial agents. Future studies will focus on investigating the stability and mode of action of these nanoparticles and exploring their application in food packaging for antimicrobial purposes, emphasizing their safety, effectiveness, and potential to extend shelf life.