Novel chlorine-extending polymer coating with prolonged antiviral activity against SARS-CoV-2.

We previously reported a novel polymeric surface coating, namely, HaloFilm™ that can immobilize and extend the antimicrobial activity of chlorine on surfaces. In this study, we demonstrated the continuous antiviral efficacy of HaloFilm when applied on stainless steel and cotton gauze as two representative models for non-porous and porous surfaces against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Forty-eight hours post HaloFilm application and chlorination and 2 h post the viral challenge, the inoculum titre was reduced by 2.25 ± 0.33 and ≥4.36 ± 0.23 log10 TCID50 on non-porous and porous surfaces, respectively. The half-life of the virus was shorter (13.86 min) on a HaloFilm-coated surface than what has been reported on copper (46.44 min).

Colorimetric detection of residual quaternary ammonium compounds on dry surfaces and prediction of antimicrobial activity using bromophenol blue.

Controlling and monitoring the residual activity of quaternary ammonium compounds (QACs) are critical for maintaining safe yet effective levels of these agents in the environment. This study investigates the utility of bromophenol blue (BPB) as a safe, rapid and user-friendly indicator to detect in situ residual QACs dried on hard, non-porous surfaces, as well a means to assess their antimicrobial efficacy. At pH 7, BPB has a purple colour which turns blue upon its complexation with QACs such as didecyldimethylammonium chloride (DDAC). BPB itself has no antimicrobial properties up to 400 ppm. Within the range of 0-400 ppm, BPB colour change was tied to specific DDAC antimicrobial performances with a detection threshold of 100 ppm. BPB concentration and application volume could be adjusted such that a colour shift from purple to blue correlated with a set percent reduction (>99·9%) in test bacteria (Staphylococcus aureus and Klebsiella aerogenes). The BPB solutions developed in this study yielded similar colour shifts on polycarbonate and stainless steel surfaces and did not cross-react with chemical ingredients commonly found in sanitizers and disinfectant products. Overall, this study suggests that BPB provides a simple solution to safely monitor the post-application level and biocidal activity of residual dried QACs on surfaces.

Impact of pH on citric acid antimicrobial activity against Gram-negative bacteria.

The antimicrobial activity of citric acid (CA) is often evaluated without pH adjustment or control and its impact on micro-organisms is better understood in acidic conditions. However, the biocidal action of the fully ionized CA molecule, predominantly available at higher pH, has not been previously investigated. The objective of this study was to evaluate the antimicrobial effect of high (10%) and low (1%) concentrations of CA, each adjusted over a wide range of pH values (4·5, 6·5 and 9·5) relative to the controls exposed to corresponding pH levels alone (no CA). The viability and morphology of Escherichia coli and Klebsiella aerogenes were evaluated using a culture-based enumeration assay in parallel with direct SEM imaging. Overall, the highest membrane damage and loss in viability were achieved with 10% CA at pH 9·5, which yielded at least 4·6 log10 CFU per ml (P < 0·001) reductions in both organisms. Insight into the superior efficacy of CA at high pH is proposed based on zeta potential measurements which reveal a more negatively charged bacterial surface at higher pH. This pH-dependent increase in surface charge may have rendered the cells potentially more sensitive towards chelants such as CA3- that interact with membrane-stabilizing divalent metals.