Evaluation of the genetic effects of the in vitro antimicrobial activities of Rhazya stricta leaf extract using molecular techniques and scanning electron microscope

Abstract

Rhazya stricta plants have always played a major role in the treatment of human and animal diseases and it has main role in the folk medicine. The aim of this study was to explore the potential antimicrobial activities of the aqueous leaves extract of R. stricta on Gram-negative and Gram-positive food-borne bacteria and evaluate the antimicrobial effect at the molecular level. The results indicate that the aqueous leaves extract of R. stricta exhibited the antimicrobial activity against tested microorganisms. A clear, but significantly smaller, inhibition zones were formed after the treatment of two Gram-negative bacteria (Escherichia coli and Aeromonas hydrophila) and one Gram-positive bacteria (Staphylococcus aureus) with the aqueous leaves extract of R. stricta (50 mg) comparing with those formed after the treatment with streptomycin (15 mg). Moreover, the results obtained after the treatments of bacterial strains with elevated concentrations of aqueous extracts of the wild plant of R. stricta leaves reveled that the extract has potent lethal activities as the growth turbidity decreased as the concentration or time of exposure increased. In addition, the observation by the scanning electron microscope showed that cells of the bacterial strains were damaged after the treatment with plant extracts. The noticed antimicrobial effect was explored at the molecular level, using restriction fragment length polymorphism (RFLP) analysis of the plasmid DNA and random amplification of polymorphic DNA (RAPD) analysis of the genomic DNA extracted from the control (untreated) and R. stricta leaf extract-treated bacterial strains. The results demonstrate polymorphic band pattern for most treated microbes compared with the wild type (untreated) strain. Concerning gene expression under the same conditions, total protein contents of the three treated bacteria showed significantly gradual increase in all of the treatment doses compared to control. In addition, the SDS-PAGE of the bacterial cellular proteins resulted in the induction of some protein bands under the treatment conditions. All these results strongly point out the mutagenicity, lethal and antimicrobial effect of the leaves extract of R. stricta. The results indicate the possibility of using the leaves extract of R. stricta as a source of antibacterial compounds for treatment of infections caused by multi-drug resistant (MDR) bacterial pathogens.

Keywords: Medicinal plants, Rhazya stricta, antimicrobial, mutagenicity, RAPD, RFLP, SEM, E. coli, S. aureus, A. hydrophila

African Journal of Biotechnology Vol. 12(21), pp. 3171-3180