The need for in-house efficacy testing and assessment of the antimicrobial properties of silver nanoparticle (Ag+)-impregnated showerheads against Pseudomonas aeruginosa intended for healthcare waters in high-risk patient settings

Abstract

Pseudomonas aeruginosa is a Gram-negative water-borne opportunistic pathogen. Reservoirs of bacteria can infect vulnerable populations. Mitigation of this risk in healthcare includes regular microbiology monitoring and chemical/thermal disinfection of outlets. Where contamination is persistent, point-of-use filters/antimicrobial showers may be used to reduce bioburden. In this study, the efficacy of a silver-impregnated (Ag+) antimicrobial showerhead against P. aeruginosa was tested, under simulated conditions.Test (excised from antimicrobial [Ag+] showerhead) and control (stainless-steel) coupons (∼1cm2; n=108) were inoculated with 10μL (∼103 colony forming units [CFU]) P. aeruginosa (NCTC 10662 and wild-types) and overlaid with coverslips. Coupons were incubated at ambient temperature (∼40% relative humidity) for 0 minutes, 30 minutes, 2 hours, 4 hours, 24 hours. Coupons and coverslips were transferred to neutraliser solution followed by bead washing for bacterial recovery and enumeration.Contamination ranged from ∼2.90-log10 CFU (±0.14-log10; type-strain) to ∼3.02-log10 CFU (±0.16-log10; wild-types). No significant reductions in P. aeruginosa bioburden were observed against either of the three strains (P>0.05). Analogous bacterial decline was noted between the test and control (falling to below the detection limit) between 4-24 hours, possibly due to desiccation.Whilst being an economically and environmentally friendly option, antimicrobial showers may not be appropriate to lessen bioburden in healthcare waters. Previous research has demonstrated the bactericidal effects of silver-ions, however this was not established in our study. Although the concentration of silver in the test materials was unknown, our findings suggest that antimicrobial showerheads may require higher concentrations of silver-ions, to display antimicrobial activity. Further testing is required to determine efficacy against biofilms.