Atomic force microscopy analysis shows surface structure changes in carvacrol-treated bacterial cells

Carvacrol is a major component in some essential oils such as oregano and thyme and its inhibitory effect on the growth of various microorganisms is well documented. However, the active mechanism of carvacrol, as well as that of other essential oil components, has not yet been fully established and has generally not been well investigated. In this study, the antimicrobial activity of carvacrol against some Gram-positive and Gram-negative food-related bacterial strains was preliminarily verified and the effect of carvacrol on their cell envelope was further investigated by atomic force microscopy analysis. The atomic force microscopy images of the cells treated with carvacrol 3.3 mM for 1 h were analyzed by an appropriate software in order to visualize the effect of the treatment and to determine the values of cell surface roughness and some biometric parameters (cell length and width). The results showed that all microorganisms tested were sensitive to carvacrol both in solid and liquid media. Furthermore, images of cells of all strains treated with carvacrol exhibited appreciable modifications, indicating a change in cell surface structure. Finally, both length and diameter of the microorganisms decreased after contact with carvacrol.