Impact of the changes in bacterial outer membrane structure on the anti-bacterial activity of zinc oxide nanoparticles

Metal and metal oxide nanoparticles (NPs) have been increasingly utilized in many industries to harness their documented antibacterial properties. However, the mechanism(s) of action is still debated in the literature. The aim of this study is to understand how changes in outer membrane charge of a test bacteria Haemophilus influenzae alter the antibacterial activity of ZnO NPs of average sizes of 20 nM and 60 nM. H. influenzae outer membrane charge was altered through use of the wild strain (Rd) and mutant lines H543 and H446. Results indicate that antibacterial effects are both concentration and size dependent, with smaller NPs causing increased antibacterial response. Most critically, antibacterial assays and collected TEM images demonstrate that increasing negative charge on the outer membrane of bacteria decreased the antibacterial activity of the ZnO NPs. Finally, this work demonstrates the possibility of using ZnO NPs to treat H. influenzae infection in clinical settings.