Thesis & Dissertations

The discovery of antibiotics is recognized as a major milestone in the history of chemotherapy discovery, as it benefited humankind in treating infectious diseases that were otherwise notorious to available medication. However, the misuse of antibiotics followed by natural selection of resistant strains of infectious microorganisms hindered the efficacy of these antimicrobial agents, and led to higher morbidity and mortality rates coupled with increased health-care costs. Therefore, the quest for the discovery of novel antimicrobial agents should continue. Medicinal plants, being the compelling wellsprings of both conventional and current pharmaceuticals, constitute an important source for protective, preventive, and curative medicine. Plants of the genus Rubus have been used for centuries for diverse medicinal purposes. To the best of our knowledge, the antimicrobial efficiacy of Rubus hedycarpus, which is distributed across Lebanon at different altitudes, has never been reported before. Thus, the goal of this study is to evaluate the antimicrobial activity of methanolic and aqueous extracts of different parts of Rubus hedycarpus collected from three different altitudes in Lebanon against multiple Gram-positive (Streptococcus pneumoniae and Staphylococcus aureus) and Gram-negative bacteria (Escherichia. coli and Klebsiella pneumoniae). Extracts from plants collected from different altitudes displayed similar activities. Overall, the extracts exhibited good antibacterial activity against Staphylococcus aureus and Escherichia coli but not against Streptococcus pneumoniae and Klebsiella pneumoniae as determined by measuring the inhibition zones in plate-diffusion assays. The minimal inhibitory concentration (MIC) ranged from 0.0078125 to 0.125 μl-sample/μl against Staphylococcus aureus. The potency of the various extracts was assessed by measuring the minimal bactericidal concentration (MBC). The leaf-in-methanol and leaf-in-water extracts were found to be the most effective against MRSA with MBC of 0.0078125 μl-sample/μl, while the juice was most potent against E. coli with MBC of 0.0078125 μl-sample/μl. To visualize the effect of the extracts on the structural and morphological features of the microorganisms, Transmission Electron Microscopy (TEM) images of treated microorganisms were collected and compared to those of untreated ones. Overall, the Rubus hedycarpus extracts induced irreversible deformations and damage to the cell membranes of the microorganisms leading to the leakage of cytoplasmic components and eventual cell death. In addition, vacuolization and shrinkage of the cytoplasm were observed, thus confirming the bactericidal effects of the extracts. Furthermore, Time-Kill curves were plotted to determine the time needed by the extract to eradicate the test microorganisms at MBC. The antibacterial extracts tested in the present study were particularly effective with respect to the time needed to exert lethal effect on the microbial growth, and induced 100% killing of the test microorganisms within 10-18 h at the respective MBC. Finally, phytochemical analysis was conducted to decipher the active ingredients in the Rubus hedycarpus extracts. The extracts were screened for saponins, terpenoids, flavonoids, anthraquinones, steroids, triterpenoids, tanins, alkaloids, glycosides, and total phenol content.