Bacteria and bacteriophage inactivation by silver and zinc oxide nanoparticles

Microbial contaminants such as bacteria and viruses are of great concern in water. As nanotechnology continues to grow, understanding the interactions of nanoparticles with bacteria and viruses is important to protect public health and the environment. In this study, the effect of two commonly used nanoparticles, silver nanoparticles (AgNPs, average particle size = 21 nm) and zinc oxide nanoparticles (ZnO NPs, average particle size = 39 nm), on the growth of bacteria (Eschericia coli) and bacteriophages (MS2) were evaluated using a standard double agar layer (DAL) method and a turbidimetric microtiter assay. A 1-h prior exposure of MS2 to nanoparticles did not inactivate MS2 at the highest nanoparticle concentrations tested (5 mg/L total Ag and 20 mg/L ZnO). No bacteriophage inactivation was observed in the presence of AgNPs, Ag+/AgNPs (50:50 in mass ratio) or Ag+ ions, all at the total Ag concentration of 5 mg/L. In a binary (bacteria–phages) system where the E. coli host was exposed to MS2 and nanoparticles simultaneously, the dynamic changes of active bacteria and MS2 phages during incubation demonstrated that exposure of AgNPs (5 mg/L Ag) and ZnO NPs (20 mg/L ZnO) increased the number of phages by 2–6 orders of magnitude. These results suggested that exposure of nanoparticles could greatly facilitate bacterial viruses like MS2 to infect the E. coli host.