Mechanistic insights into the microbicidal activity of nanoparticles derived from high molecular weight fucoidan fraction extracted from Korean Undaria pinnatifida.

The rise of antimicrobial resistance underscores the necessity for novel and effective agents. This study investigates the antimicrobial properties of CDs (FPCDs) and AgNPs (FPAgNPs), synthesized for the first time using high-molecular-weight fucoidan (FP) fraction from Korean Undaria pinnatifida. FP, FPCDs, and FPAgNPs were characterized using XPS and FTIR techniques. The average sizes of FPCDs and FPAgNPs were found to be 4 nm and 22 nm, respectively. Both nanoparticles showed remarkable antimicrobial activity against E. coli, B. subtilis, P. aeruginosa, and C. albicans strains. In well diffusion, FPAgNPs (15.89-18.28 mm) had smaller zone of inhibition (ZOI) than FPCDs (17.46-25.02 mm). In disk diffusion, FPAgNPs showed 12.98-19.71 mm ZOI with highest in E. coli, whereas FPCDs displayed 13.72-17.13 mm ZOI for all pathogens except P. aeruginosa. The reactive oxygen species (ROS) were observed to be the main mechanism behind the antimicrobial potential of FPCDs and FPAgNPs. Further, the structural anomalies in the pathogens were observed by phase contrast and scanning electron microscopy. In addition, FPCDs demonstrated proliferative growth in specific cell lines, whereas FPAgNPs displayed toxicity. This study presents the synthesis of FPCDs and FPAgNPs, highlighting their antimicrobial potential through DNA damage and elevated intracellular ROS levels.