Laboratory Evaluation of a Quaternary Ammonium Compound-Based Antimicrobial Coating Used in Public Transport during the COVID-19 Pandemic

Abstract

The virucidal activity of the Zoono Z71 Microbe Shield surface sanitizer and protectant, a quaternary ammonium compound (QAC)-based antimicrobial coating that was used by the United Kingdom rail industry during the COVID-19 pandemic, was evaluated, using the bacteriophage ɸ6 as a surrogate for SARS-CoV-2. Immediately after application and in the absence of interfering substances, the product effectively reduced (>3 log₁₀) the viability of ɸ6 on some materials that are typically used in rail carriages (stainless steel, high-pressure laminate, plastic). If, after the application of the product, these surfaces remained undisturbed, the antimicrobial coating retained its efficacy for at least 28 days. However, efficacy depended on the material being coated. The product provided inconsistent results when applied to glass surfaces and was ineffective (i.e., achieved <3 log₁₀ reduction) when applied to a train arm rest that was made of Terluran 22. Regardless of the material that was coated or the time since application, the presence of organic debris (fetal bovine serum) significantly reduced the viricidal activity of the coating. Wiping the surface with a wetted cloth after the deposition of organic debris was not sufficient to restore efficacy. We conclude that the product is likely to be of limited effectiveness in a busy, multiuser environment, such as public transport. IMPORTANCE This study evaluated the performance of a commercially available antimicrobial coating that was used by the transport industry in the United Kingdom during the COVID-19 pandemic. While the product was effective against ɸ6, the efficacy of the coating depended upon the material to which it was applied. Similarly, and regardless of the surface material, the presence of organic debris severely impaired viricidal activity, and efficacy could not be recovered through wiping (cleaning) the surface. This highlights the importance of including relevant materials and conditions when evaluating antimicrobial coatings in the laboratory. Further efforts are required to identify suitable infection prevention and control practices for the transport industry.

Keywords: COVID-19; QAC; SARS-CoV-2; antimicrobial coating; public transport; ɸ6.

FIG 1

Survival of ɸ6 over 60 min on glass coupons coated with Zoono Z71 (gray circles) and noncoated coupons (black circles) that were processed in parallel. Coupons were coated by either spraying (n = 2 experimental trials) or pipetting 75 μL on each coupon (n = 1 experimental trial). All conditions were tested in triplicate on the three experimental trials, and individual results are expressed as PFU per coupon (PFU/coupon). The individual dots represent the results for individual coupons, and the lines show the mean for each time point. No ɸ6 could be recovered from 3 out of the 9 coated coupons after 30 min or from 7 out of the 9 coated coupons after 60 min. The concentrations of these samples were assumed to be 20 PFU/coupon, which is the theoretical limit of detection, for the analysis.

FIG 2

Efficacy of Zoono Z71 within a 120-minute contact time, when applied to a tray table (Side A, HPL; Side B, CSS), in the presence or absence of FBS, after wiping with a wetted cloth, in comparison with nonwiped controls. Two wiping protocols that differed in the number of wipes were applied. The efficacy is expressed as the mean log₁₀ reduction, calculated by subtracting the mean ɸ6 PFU recovered on coated tray tables with or without FBS and with or without wiping from the mean ɸ6 PFU recovered from the matched noncoated control tray tables, after 120 min of contact time in two independent experimental trials with three test areas (containing one droplet of ɸ6 each) being analyzed per condition. The error bars represent the standard deviation. Undetected virus observations were assumed to have a concentration of 20 PFU/replicate, which is the theoretical detection limit, for the analysis.

FIG 3

Top left, Terluran 22 arm rests; top right, plastic coated hand poles; bottom left, HPL tray table (Side A); bottom right, CSS tray table (Side B).