Effects of Antimicrobial Air Filters on the Viability and Culturability of Airborne Bacteria

Abstract

The effects of antimicrobial filters on the viability and culturability of Escherichia coli and Bacillus subtilis in terms of antimicrobial nanoparticle concentrations and bacterial residence time on filters were investigated. The Sophora flavescens nanoparticles were used to prepare antimicrobial filters. Although the loss of bacterial viability and culturability increased with increasing antimicrobial nanoparticle concentrations on the filter, the intensity of the antimicrobial reactions differed: The culturability loss was more than twice the viability loss under all conditions, and a maximum of 45 ± 12% to 57% ± 12% of bacteria entered the viable but nonculturable (VBNC) state. Testing filters at various bacterial residence times, 87 ± 4% to 92 ± 0.1% of bacteria lost culturability after 60 min due to natural decay, whereas only 10 ± 4 to 13 ± 6% lost viability. Additionally, the number of VBNC bacteria increased with increasing residence time. On antimicrobial filters, the culturability reduction trends of both bacterial species were similar; however, their viability reduction trends differed: The E. coli viability decreased gradually from 77 ± 10% to 64 ± 7% over 60 min, whereas that of B. subtilis decreased dramatically from 70 ± 13% to 22 ± 0.1% over the same period. As residence time increased, the proportion of E. coli and B. subtilis cells that entered the VBNC state decreased due to the increased antimicrobial effect on bacterial viability.