Essential Oil Disinfectant Efficacy Against SARS-CoV-2 Microbial Surrogates

Reports of COVID-19 cases potentially attributed to fomite transmission led to the extensive use of various disinfectants to control viral spread. Alternative disinfectants, such as essential oils, have emerged as a potential antimicrobial. Four essential oil blends were tested on three different surfaces inoculated with a coronavirus surrogate, bacteriophage Phi 6, and a bacterial indicator, Staphylococcus aureus. Log10 concentration reductions were analyzed using GraphPad Prism software. Data collected in this study show that the application of dilute essential oil disinfectants using a spray delivery device is an effective way to reduce concentrations of bacterial and viral microorganisms on ceramic, stainless steel, and laminate surfaces. Surrogate viruses were reduced up to 6 log10 PFU and bacterial were reduced up to 4 log10 CFU. Although surfaces are no longer considered a high risk fomite for COVID-19 transmission, the disinfection of microorganisms on surfaces remains an important consideration for high touch areas in hospitals, waiting rooms, etc. The application of spray disinfectants, based on essential oil blends, provides a rapid and effective means to reduce microbial contamination on high-touched surfaces.

A global disinfectant standard for cleanrooms: Presenting a harmonised approach

Disinfectant efficacy testing is an essential part of a facility contamination control strategy. Pharmaceutical and healthcare products facilities must know that the products they are using can achieve effective levels of microbial kill across a range of surface types. The problem faced by microbiologists and production managers is that the various national and international standards use different methodologies. In addition, these standards and methods have not been written specifically for cleanrooms and the microbial test panels and logarithmic reduction expectations are not considered suitable. In order to develop an international standard suitable for all pharmaceutical facility cleanrooms, Ecolab has developed the Validex™ method, which is independently assessed in this paper. This method involves using 2 cm diameter disks, to target a 3 log reduction for vegetative bacteria in 5 minutes; and a 2 log reduction for fungi and bacterial spores in 10 minutes. The key criteria and rationale for selection, along with the methodology, are presented in this paper.

Disinfectant Efficacy Against Dry Surface Biofilms of Staphylococcus Aureus and Pseudomonas Aeruginosa Is Product, Time Point and Strain Dependent

Background: Globally, healthcare associated infections (HAI) are the most frequent adverse outcome in healthcare delivery. Although bacterial biofilms contribute significantly to the incidence of HAI, few studies have investigated the efficacy of common disinfectants against dry surface biofilms (DSB). The objective of this study was to evaluate the bactericidal efficacy of seven disinfectants against DSB of Staphylococcus aureus and Pseudomonas aeruginosa. We hypothesized that overall, hydrogen peroxides, sodium dichloro-s-triazinetrione and quaternary ammonium compounds plus alcohol disinfectants will be more bactericidal against DSB than quaternary ammonium. We also hypothesized that regardless of differences in product chemistries, higher bactericidal efficacies against DSB will be exhibited after 24 h of dehydration compared to 72 h.Methods: Wet surface biofilms of S. aureus and P. aeruginosa were grown following EPA-MLB-SOP-MB-19 and dehydrated for 24 h and 72 h to establish DSB. Seven EPA-registered disinfectants were tested against dehydrated DSB following EPA-MLB-SOP-MB-20. Results: Overall, quaternary ammonium plus alcohol, sodium dichloro-s-triazinetrione, and hydrogen peroxide products were more efficacious against DSB than quaternary ammoniums for both tested strains. While there was no significant difference in biofilm killing efficacies between 24 h and 72 h S. aureus biofilms, significantly higher log10 reductions were observed when products were challenged with 24 h P. aeruginosa DSB compared to 72 h P. aeruginosa DSB. Conclusion: Strain type, active ingredient class, and dry time significantly impact disinfectant efficacy against DSB of S. aureus or P. aeruginosa.

Why it’s time to strengthen and widen the microbial test panel

The testing of culture media, and conducting microbiological method suitability studies, disinfectant efficacy studies, Antimicrobial Effectiveness Test (or Preservative Efficacy Test) and associated activities, requires the use of a test panel of microorganisms. These organisms need to be representative of the intended application and be of a suitable range in order to demonstrate that a low level of viable cells can be recovered without any indication of the inhibition of growth or excessive growth-promotion (typically defined as the recovery of between 50 to 200% of the challenge count). This activity provides the basis for the release of culture media or for verifying that a method is suitable for recovering any microorganisms that might be present in a product sample. This approach has been established for several decades and in many cases the types of organisms selected for the panel are drawn from guidance presented in the major pharmacopeia. The test panels of organisms recommended by compendia along with specific standards are in place to allow for reproducibility between laboratories. In the case of most standards (such as the disinfectant efficacy norms), these are designed to be multi-industry. Hence the presented organisms may or may not be suitable for the intended application. In addition, with the compendia, all too often the organisms recommended for, say, the Microbial Limit Test method verification, are applied to the release of all culture media used for all activities, be that the test for sterility or for the recovery of organisms from water systems. Not only is this inappropriate – for the microbiologist should be reviewing the panel and deciding upon the appropriate organisms – the recommended panels have not kept pace with improvements with our understanding of the types of microorganisms likely to cause contamination. Take, for example, the inclusion of Salmonella in the panel for the recovery of so-called ‘objectionable microorganisms’ for use with the Microbial Limits Test ¹. To my knowledge and based on discussions with microbiologists over a couple of decades, no Salmonella has ever been recovered from a raw material. Equally the selection, especially in relation to the testing of culture media used for cleanroom environmental monitoring, has not moved forwards with the findings from the human microbiome project and the depth of species richness found on the human skin microbiome. The argument that the test panel quoted in the compendia is representative and thus if culture media release testing can recover such organisms then it can reasonably be assumed that any other similar organisms can be recovered does not really hold up. Unless, that is, the only concern is with the recovery of non-fastidious mesophilic organisms. Instead, I maintain that in terms of the appropriate panel, this should be based on: • What is currently being recovered, and • What should theoretically be recovered.