Rapid determination of the antimicrobial properties of surfaces using an enzymatic activity surrogate

Abstract

Typical approaches for assessing the antimicrobial activity of metals-based surfaces involve the contact of a bacterial culture with the surface for a period of time, followed by culturing on agar plates to assess the decrease in microbial viability versus controls. This is a time-consuming methodology requiring at least 24 h to produce a set of results, which can be a bottleneck for productivity in novel materials development. An enzyme-based method was shown to be a satisfactory and much more rapid surrogate test for this application. A β-galactosidase solution was applied to copper, silver, and zinc-based antimicrobial surfaces for up to 1 h, and then the rate of colour development at 578 nm was monitored for a few minutes after addition of the chromogenic enzyme substrate chlorophenol red-β-d-galactopyranoside (CPRG). Highly active antimicrobial surfaces were detected by a lack of colour development, due to enzyme inhibition by the metals. The enzymatic reaction rates were quantified and compared, demonstrating that the copper sample showed the greatest inhibition effect followed by the silver and zinc samples. The antimicrobial activity was quantified using bacteria and the plate count method, and the results correlated well with this enzyme assay, demonstrating that the metals-based antimicrobial activities of both hard and soft (textile) surfaces could be quickly assessed with this enzyme-based methodology.