Morphological Changes in the Overall Mycobacterium tuberculosis H37Ra Cell Shape and Cytoplasm Homogeneity due to Mutellina purpurea L. Essential Oil and Its Main Constituents

Objective: The aim of this study was to evaluate the antimycobacterial activity of the essential oil (EO) of Mutellina purpurea L. and its main constituents against the M. tuberculosis H 37 Ra strain. Materials and Methods: The M. purpurea EO was obtained by hydrodistillation, while its main constituents were purchased. The minimal inhibitory concentration values were determined by the log2 dilution method. Visualization of the effects of the tested substances on M. tuberculosis was performed using a transmission electron microscope (TEM). Mathematical shape descriptors such as area, circularity, aspect ratio and roundness were calculated to describe morphological changes in bacterial cell shape. Results: The EO of M.purpurea and all substances tested in this experiment showed a significant antimycobacterial activity. The most active was α-pinene followed by bisabolol and myrcene (8, 16 and 32 µg/ml, respectively). The EO and limonene exhibited the same antimicrobial activity (64 µg/ml). The TEM images and shape descriptors showed significant changes in the overall tuberculosis cell shape and cytoplasm homogeneity (uniformity and consistency) Conclusions: In this study, the low molecular weight compounds of mono- and sesquiterpenes penetrated/destabilized the complex mycobacterial cell wall and decreased its viability. There is a need for further experiments to explain the mechanism of action of these small particles.