Phytochemical-Mediated Green Synthesis and Physicochemical Characterization of Cadmium Sulphide Nanocrystals from Morinda citrifolia with Antibacterial Activity Against Multidrug-Resistant Enterobacteriaceae

The rapid emergence of multidrug-resistant (MDR) Enterobacteriaceae poses a significant challenge to the effective management of infectious diseases, necessitating the development of novel antimicrobial agents. In this study, cadmium sulphide (CdS) nanocrystals were synthesized through a green approach using aqueous leaf extract of Morinda citrifolia as a natural reducing and stabilizing agent, and their antibacterial activity against MDR Enterobacteriaceae was investigated. Thirteen clinical Enterobacteriaceae isolates were identified using conventional morphological and biochemical methods, with all but one isolate exhibiting multidrug resistance. Successful synthesis of CdS nanocrystals was confirmed by a characteristic dark yellow coloration and a UV–Visible absorption peak at 369 nm. Comprehensive physicochemical characterization using SEM, EDX, XRF, XRD, and FTIR revealed heterogeneous semi-spherical crystalline CdS nanocrystals (hawleyite phase) containing cadmium and sulfur as the principal elemental constituents. At the same time, FTIR analysis indicated the presence of phytochemical functional groups involved in nanoparticle stabilization. The biosynthesized CdS nanocrystals exhibited appreciable antibacterial activity against selected MDR isolates at concentrations of 120 and 240 µg/mL, with a minimum inhibitory concentration of 120 µg/mL for all tested organisms and bactericidal activity against selected Proteus spp. and Klebsiella pneumoniae isolates. These findings demonstrate that M. citrifolia-mediated CdS nanocrystals represent a promising green-synthesized antimicrobial nanomaterial with potential applications against MDR bacterial pathogens. Further studies on toxicity, biocompatibility, and in vivo efficacy are warranted to support their therapeutic development.