Shape-dependent antibacterial activity of silver nanoparticles on Escherichia.coli and Enterococcus.faecium bacterium

Silver nanoparticles (AgNPs) have been shown to exhibit strong antibacterial activity against both Gram-positive bacteria and Gram-negative bacteria including antibiotic resistant strains. The antibacterial activity of AgNPs against Escherichia coli and Streptococcus mutans (S. Mutans) has been reported and found to be size dependent. This study aims to compare the bactericidal effect of different shaped AgNPs (spherical and truncated octahedral) against E.coli and E.faecium. The antimicrobial activity of a range of concentrations (50, 100, 1000μg/ml) was determined over 24 hours using both optical density and viable counts. Truncated octahedral AgNPs (AgNoct) were found to be more active when compared with spherical AgNPs (AgNS). The difference in shape resulted in differences in efficacy which may be due to the higher surface area of AgNOct compared to AgNS, and differences in active facets and surface energies, with AgNPs having a bacteriostatic effect and AgNOct is being bactericidal after 4 hours. The results suggest that AgNPs can be used as effective growth inhibitors in different microorganisms, rendering them applicable tovarious medical devices and antimicrobial control systems.