Mixtures of Essential Oils in an Air Conditioning Prototype to Reduce the Prevalence of Airborne Pathogenic Bacteria

Abstract

The rationale for this work was to test the possibility of creating a protective atmosphere by using natural compounds to minimize hazards from chemicals and to control the risk of common infections. The antimicrobial activities of essential oils of Agronis fragrans, Cinnamomum zeylanicum, Lavandula angustifolia, Melaleuca alternifolia (tea tree), Melaleuca nesophila (honey myrtle), Pelargonium x asperum (geranium), Pogostemon cablin (patchouli), Thymus serpyllum, and Thymus vulgaris were evaluated against an array of environmental-borne pathogenic bacteria. Gram-positive bacteria included Bacillus subtilis and Staphylococcus aureus; four Gram-negative bacteria covered Acinetobacter baumanii, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa. In addition, eleven isolates of methicillin-resistant S. aureus (MRSA) and a multidrug-resistant A. baumanii were incorporated. In agar disc diffusion tests, cinnamon had shown the strongest activity that could inhibit all pathogens, followed by lemon thyme, honey myrtle and lavender, while pachouli exhibited the weakest inhibition. Though fragonia possessed a broad range of activity against all pathogens, it did not inhibit some of the MRSA isolates. Cinnamon and lemon thyme demonstrated strong activity measured by minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations. In disk volatilization assay, thyme oil demonstrated the greatest inhibition, followed by lemon thyme, while no inhibition from patchouli was observed. Subsequently, the composition of the atmosphere generated by three different oil blends in our invented portable air-conditioning prototype was assessed. The results showed that mixture of oil blend No. 2 can produce good synergistic effect in reducing the prevalence of airborne pathogens, and thus preventing the spreading of infections.