Abstract
Hygiene and disinfection practices play an important role at preventing spread of viral infections in household, industrial and clinical settings. Although formulations based on >70% ethanol are virucidal, there is a currently a need to reformulate products with much lower alcohol concentrations. It has been reported that zinc can increase the virucidal activity of alcohols, although the reasons for such potentiation is unclear. One approach in developing virucidal formulations is to understand the mechanisms of action of active ingredients and formulation excipients. Here, we investigated the virucidal activity of alcohol (40% w/v) and zinc sulfate (0.1% w/v) combinations and their impact on a human adenovirus (HAdV) using, nucleic acid integrity assays, atomic force microscopy (AFM) and transmission electron microscopy (TEM). We observed no difference in virucidal activity (5 log10 reduction in 60 min) against between an ethanol only based formulation and a formulation combining ethanol and zinc salt. Furthermore, TEM imaging showed that the ethanol only formulation produced gross capsid damage, whilst zinc-based formulation or formulation combining both ethanol and zinc did not affect HAdV DNA. Unexpectedly, the addition of nickel salt (5 mM NiCl2) to the ethanol-zinc formulation contributed to a weakening of the capsid and alteration of the capsid mechanics exemplified by AFM imaging, together with structural capsid damage. The addition of zinc sulfate to the ethanol formulation did not add the formulation efficacy, but the unexpected mechanistic synergy between NiCl2 and the ethanol formulation opens an interesting perspective for the possible potentiation of an alcohol-based formulation. Furthermore, we show that AFM can be an important tool for understanding the mechanistic impact of virucidal formulation.
Highlights
Understanding the mode of action of a biocidal products has been shown to be relevant for establishing scientific principles, improvement of biocidal products as well as usage optimization, and combatting emerging resistance by target microorganism (Myers, 2008; Condell et al, 2012)
Following the use of the BS EN14476 protocol, the virucidal activity of the different formulations after 60 min exposure in hard water but with no organic load showed that the full formulation and the formulated ethanol (RB-Full and RBEthanol) (Figure 1) showed a significant reduction in PFU/ml compared to the formulated zinc or the control containing excipients only (p < 0.05)
The formulation control (RB-Control) which contained excipients only did not show any reduction in human adenovirus type 2 (HAdV2) infectivity and the lack of virus inactivation was comparable to RB-Zinc (Figure 1)
Summary
Understanding the mode of action of a biocidal products has been shown to be relevant for establishing scientific principles, improvement of biocidal products as well as usage optimization, and combatting emerging resistance by target microorganism (Myers, 2008; Condell et al, 2012). Virucides Against Human Adenovirus their interactions with microbial targets, here viruses, informs our knowledge of mechanisms contributing to viral inactivation or viral resistance mechanisms, and contributes to improving efficacy through formulation design and better usage recommendation of the product in practice (Russell, 2003). Nonenveloped viruses offer less targets for virucidal action compared to enveloped ones. These targets comprise mainly the capsid, viral encoded receptor binding proteins and viral genomes (Maillard, 2001; Myers, 2008). The mechanisms of virucidal action against non-enveloped viruses remain poorly studied
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