Evaluation of the antibacterial activity of some plant essential oils against Ralstonia solanacearum and the molecular diagnosis of the bacterium

Mikhail, Maurice S.; Abd-Alim, Ahmed I.; Balabel, Naglaa M.; Abbas, Ahmed M.

doi:10.4103/epj.epj_254_24

Evaluation of the antibacterial activity of some plant essential oils against Ralstonia solanacearum and the molecular diagnosis of the bacterium

Authors

Abstract

Background
Evaluation of the antibacterial activity of some essential oils for controlling potato bacterial wilt.
Objective

In vitro and planta trials, five essential oils, lemongrass, eucalyptus, thyme, ginger, and peppermint, were evaluated for their aptitude to impede the progress of Ralstonia solanacearum.

Materials and methods
Five essential oils were assessed for their activity to inhibit R. solanacearum growth using the disc diffusion method. Certain volumes of each tested plant essential oil were added on filter paper discs using tetrazolium chloride agar medium, which contained the tested bacterium to obtain the proposed concentrations used to evaluate the most efficient oil for controlling potato bacterial wilt. Serological and molecular identification was also conducted.
Results and conclusion

R. solanacearum was characterized using cultural characteristics on the selective medium South Africa, “which is the most effective in suppressing the growth of contaminating microorganisms, and the highest recovery rate of the tested bacterium,” immunofluorescence antibody staining tomato bioassay test and molecular identification via real-time PCR (Taq-man) assay. In-vitro studies showed that all tested plant essential oils (lemongrass, eucalyptus, thyme, ginger, and peppermint) significantly reduced R. solanacearum progress. Eucalyptus (Eucalyptus globulus) and peppermint (Mentha piperita) essential oils were the most efficient in suppressing R. solanacearum growth, where it showed the highest mean inhibition zone, followed by thyme oil (Thymus vulgaris), lemongrass oil (Comybogen citratus), and ginger oil (Zingiber officinale), respectively. Phenotypic variances in bacterial cell construction have been noticed via a transmission electron microscope. Eucalyptus oil led to cell wall lysis, cell laceration, bubble-like structures, and degraded cellular components in bacterial cells.

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