Biogenic silver for disinfection of water contaminated with viruses

Abstract

The presence of enteric viruses in drinking water is a potential health risk. Growing interest has arisen in nanometals for water disinfection, in particular the use of silver-based nanotechnology. In this study, Lactobacillus fermentum served as a reducing agent and bacterial carrier matrix for zerovalent silver nanoparticles, referred to as biogenic Ag(0). The antiviral action of biogenic Ag(0) was examined in water spiked with an Enterobacter aerogenes-infecting bacteriophage (UZ1). Addition of 5.4 mg liter(-1) biogenic Ag(0) caused a 4.0-log decrease of the phage after 1 h, whereas the use of chemically produced silver nanoparticles (nAg(0)) showed no inactivation within the same time frame. A control experiment with 5.4 mg liter(-1) ionic Ag+ resulted in a similar inactivation after 5 h only. The antiviral properties of biogenic Ag(0) were also demonstrated on the murine norovirus 1 (MNV-1), a model organism for human noroviruses. Biogenic Ag(0) was applied to an electropositive cartridge filter (NanoCeram) to evaluate its capacity for continuous disinfection. Addition of 31.25 mg biogenic Ag(0) m(-2) on the filter (135 mg biogenic Ag(0) kg(-1) filter medium) caused a 3.8-log decline of the virus. In contrast, only a 1.5-log decrease could be obtained with the original filter. This is the first report to demonstrate the antiviral efficacy of extracellular biogenic Ag(0) and its promising opportunities for continuous water disinfection.

FIG. 1.

Inactivation of bacteriophage UZ1 in 5.4-mg-liter⁻¹ biogenic Ag⁰ suspensions, compared with the biomass-free control, the control with L. fermentum, and the control with 5.4 mg liter⁻¹ ionic Ag⁺. C_t, concentration of UZ1 determined by plaque assays (in PFU ml⁻¹); C₀, initial concentration. Error bars represent the standard deviations of triplicate experiments.

FIG. 2.

Inactivation of MNV-1 in 5.4-mg-liter⁻¹ biogenic Ag⁰ suspensions, compared with the biomass-free control. C_t, concentration of MNV-1 determined by RT-PCR or plaque assays (in gc or PFU ml⁻¹, respectively); C₀, initial concentration. Error bars represent the standard deviations of triplicate experiments.

FIG. 3.

Inactivation of bacteriophage UZ1 during continuous filtration through NanoCeram cartridge filters homogenously coated with 31.25 mg biogenic Ag⁰ m⁻². As a comparison, the inactivation by the original NanoCeram filter is presented. In a control experiment, the phage removal by the experimental setup without filter is examined as well. C_influent, concentration of UZ1 in the influent determined by plaque assays (in PFU ml⁻¹); C_effluent, concentration of UZ1 in the effluent. Error bars represent the standard deviations of triplicate influent and effluent samples.