Combating the prevalence of water-borne bacterial pathogens using anisotropic structures of silver nanoparticles

The current study aimed to investigate the antibacterial activity of different anisotropic structures of silver nanoparticles in the hexagon and spherical shapes against MDR-bacteria isolated from water sources in Egypt. The water samples collected from four different dairy farm-related sites were tested bacteriologically, followed by identification of the antibiotic-resistant profile for the isolates. The result revealed that Enterococcus spp , Proteus spp, and E . coli spp are the most common organisms in all tested water samples, and the antibiotic-resistant profile identified 11/13 waterborne isolates as MDR-bacteria. Herein, spherical and hexagonal silver nanoparticles were prepared with an average size of 26 ± 6 nm and 375 ± 80 nm, respectively, through the chemical reduction method. Further, MDR gram-positive ( Enterococcus ) and MDR gram-negative ( E . coli ) were selected for studying the antibacterial property of the synthesized AgNPs using agar well diffusion method. In another experiment, microdilution broth assay coupled with XTT assay is optimized for facilitating the testing of a broad range of AgNPs concentrations efficiently without the need for laborious preparation of the colony counting method. Our results indicated that AgNPs in spherical and hexagonal shapes are potent antibacterial against the MDR-waterborne bacteria in a dose and shape-dependent manner. The hexagonal AgNPs (h-AgNPs) express higher bactericidal activity when compared to spherical AgNPs (AgNSs) against the two tested MDR-bacteria, but the E . coli isolate more sensitive to both tested shapes of AgNPs than the Enterococus isolate. The results recommend that AgNPs can be used as efficient growth inhibitors for water-borne bacterial pathogens, making them applicable to various water filters and antimicrobial applications. Graphical Abstract