Eco-Friendly Sanitization of Indoor Environments: Effectiveness of Thyme Essential Oil in Controlling Bioaerosol Levels and Disinfecting Surfaces

Abstract

Bioaerosols and pathogens in indoor workplaces and residential environments are the primary culprits of several infections. Techniques for sanitizing air and surfaces typically involve the use of UV rays or chemical sanitizers, which may release chemical residues harmful to human health. Essential oils, natural substances derived from plants, which exhibit broad antimicrobial properties, could be a viable alternative for air and surface sanitation. The objective of this study has been to investigate the efficacy of thyme essential oil (TEO) in environmental sanitation processes. In Vitro assays through agar well diffusion, disk volatilization and tube dilution methods revealed significant antimicrobial activity of TEO 100% against foodborne and environmental isolates, with both bacteriostatic/fungistatic and bactericidal/fungicidal effects. Therefore, aqueous solutions of TEO 2.5% and 5% were formulated for air sanitation through nebulization and surface disinfection via direct contact. Bioaerosol samples and surface swabs were analyzed before and after sanitation, demonstrating the efficacy of aqueous solutions of TEO in reducing mesophilic and psychrophilic bacteria and environmental fungi levels in both air and on surfaces. The obtained results prove the antimicrobial potential of aqueous solutions of TEO in improving indoor air quality and surface cleanliness, suggesting thyme essential oil as an effective and safe natural sanitizer with minimal environmental impact compared to dangerous chemical disinfectants.

Keywords: antimicrobial activity; bioaerosol control; indoor sanitization; surface disinfection; thyme essential oil.

Figure 1

Graphic representation, not to scale, of the indoor environment utilized in the experimental sanitization procedures; asterisks indicate the bioaerosol sampling sites.

Figure 2

Total microbial levels in indoor bioaerosols before (control) and after sanitization with TEO 2.5% and 5% and H₂O₂ 0.5%. The number of colonies for plates is expressed as the mean ± standard deviation of a triplicate assay conducted at three sampling points. TEO, thyme essential oil; H₂O₂, hydrogen peroxide. Statistical significance was examined by the two-way ANOVA test with Tukey’s correction (p < 0.05) for comparisons with the control. For mesophilic bacteria, asterisks indicate the statistical significance with respect to the positive control (**** p < 0.0001); for psychrophilic bacteria, hashtags indicate the statistical significance compared to the control (^#### p < 0.0001); the absence of symbols indicates the absence of significance. Letters (a–c) indicate the statistical differences between different values; results with no significant differences receive the same letter.

Figure 3

Microbial levels on stainless-steel (a) and monolithic stoneware (b) surfaces, before (control) and after sanitization with TEO 2.5% and 5% and sodium NaClO 3%. The mean values ± standard deviation, obtained from triplicate analyses, are expressed as colony-forming units (CFU) per 1 square centimeter of sampled surface. Statistical significance was examined by the two-way ANOVA test with Dunnett correction (p < 0.05) for comparisons with each control. Asterisks indicate the statistical significance with respect to the positive control (**** p < 0.0001; *** p < 0.001; ** p < 0.01); the absence of asterisks indicates the absence of significance. Letters (a,b) indicate the statistical differences between different values; results with no significant differences receive the same letter.