Investigation of plant and fungi derived natural products for application as antimicrobial aerosols

Abstract

From the use of medicinal plants by extinct civilizations to the spawn of “The golden age” of drug discovery in the nineteenth century, natural products continue to be an invaluable source of bioactive molecules for applications spanning a broad spectrum of utility in many industries. Yet, there has been an overall decline in research efforts in bioprospection and subsequent commercial application of potentially useful natural products due to advancements in technologies associated with synthetic chemistry. Thus, it is apparent that risk-friendly institutions now play a greater role in research and development of chemical products that exploit bioactive properties of natural products for commercial application. This study investigated the potential of plant and fungi derived natural products to develop an antimicrobial aerosol spray for future application in indoor environments to control bioaerosol levels in both residential and commercial settings. The present industry-sponsored work represents a significant portion of the research and development pipeline that encompass bioprospection of natural sources to the successful development of a working aerosol prototype. Two plant essential oils of Leptospermum scoparium (Mānuka) and Cryptomeria japonica (Sugi) and solvent extracts of six filamentous fungi isolated from various New Zealand environments were investigated. In short, the spectrum of bioactivity and antimicrobial efficacies against common environmental organisms were assessed via in vitro plate-based assays. In addition, their physicochemical properties were evaluated to shortlist the most promising candidate for aerosol application. Next, a prototype aerosol spray was developed by incorporating the plant essential oils and the antimicrobial efficacy was assessed by simulating an end-user application scenario in a controlled environment. Lastly, the natural product was chemically characterised via Gas chromatography coupled to mass-spectrometry to understand the composition and variation between extracts prepared in different batches to facilitate decision making processes in future product manufacturing. From these investigations, the two plant extracts were identified as the most suitable candidates for product development based on their broad-spectrum activity, commercial feasibility and preferable physicochemical properties for formulation development. Of these candidates, the Mānuka oil aerosol prototype exhibited superior antimicrobial efficacy compared to Sugi essential oil spray and is recommended for further commercial investigations.