Bactericidal action of lemon grass oil vapors and negative air ions

In this study, bactericidal efficacy and mechanism of action of lemon grass oil vapors against Escherichia coli were investigated. Next, in order to develop the application of the vapor as room/surface disinfectant and to study its integration with another antimicrobial agent i.e. negative air ion (NAI), a special set-up was designed and kill time assays were conducted. Zone of inhibition (56 mm) due to the vapor phase antimicrobial activity evaluated using disk volatilization assay was compared with direct assay (well diffusion assay) in liquid phase (i.e. 20 mm for the same dose of oil). The Chemical analysis of the Essential oil vapor has been done by SPME GC-MS and -Myrcene (3.5%), Limonene (30.3%), Camphene (6.5%). alpha-Citral (17.6%), beta-Citral (11.3%), 6-methyl hepten-2-one (14.6%) and linalool (1.5%) were recorded as major components. The morphological and ultrastructural alterations in vapor treated E. coli cells were studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Results of the kill time assays demonstrated that the combination of NAI with lemon grass oil vapors has a greater bactericidal effect (100% reduction in viability) than NAI alone (42%) or vapors alone (78%) within 8 h exposure. Present results indicate that lemon grass oil is highly effective in vapor phase and its efficacy can further be enhanced by integration with Negative air ion (NAI) for reducing the viable microbial load. The integration described here offers a novel technique for reducing the concentration of E. coli on surfaces/indoor spaces. (C) 2011 Elsevier Ltd. All rights reserved.