Morphological changes in Enterococcus faecium on exposure to Citrus essential oils in vapor phase as determined by TEM, SEM and AFM

Abstract

The antimicrobial effects of essential oils in vapor phase have been previously reported although the mechanism whereby they bring about their effect continues to be investigated. Morphological changes give some indication of the extent of the damage to cells brought about by exposure to essential oils and may provide a means of substantiating the physiological and biochemical changes that are integral to the antimicrobial effect. In this study, the morphological changes that occur during exposure of Enterococcus faecium to a Citrus essential oil in vapor phase has been investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM) and atomic force microscopy (AFM). TEM shows membrane damage, vacuole formation and leakage of cytoplasmic material, SEM shows deformation of shape, whereas AFM, which gives the most information, confirms the deformation, which could be seen even after 15 minutes exposure using this method.