Antibacterial activity and, Phytochemical screening of selected Tanzanian medicinal plants

Abstract

Background: With the currently limited number of antibacterial drugs and the ever increasing antimicrobial resistance, it is imperative that new antibacterial drugs be continuously discovered. Natural sources especially plants are cheaper, rich and diverse sources of potentially active and safe antimicrobials. Guided searches especially ethno-botanical surveys greatly focus this process since plants screening for bioactivities is guided by the ethno medicinal applications of the plants, making it resources-effective. Purpose of the study: This study aimed to investigate the antibacterial activities of plants used for infectious conditions among the local communities in Southern highlands of Tanzania. The study also aimed to determine the phytochemical compositions of the active extracts and development of their thin layer chromatography (TLC) profiles with subsequent bioautography. Methods: A total of eight plant samples were collected from Njombe and Iringa regions following ethno-medicinal information obtained from the indigenous. The collected parts were air dried before pulverization and extraction by repeated cold maceration using 80% aqueous ethanol. After drying in vacuo, the obtained extracts were tested for antibacterial activities by broth microdilution assay against both standard and clinical isolates of bacteria. Standard bacteria were of the American Type Culture Collection (ATCC) namely Escherichia coli (ATCC 25922), Klebsiella pneumoniae (ATCC 700603), Pseudomonas aeruginosa (ATCC 27853), Salmonella typhi (ATCC 8385) and Staphylococcus aureus (ATCC 25923). The clinical isolates included; Styphylococcus aureus, methicillin resistant Staphylococcus aureus (MRSA), Klebsiella pneumonia, Pseudomonas aeruginosa, Escherichia coli and Salmonella typhi. Antibacterial activities were determined in terms of minimum inhibitory concentrations (MICs) obtained as the mean values of duplicate assays. Phytochemical screening, TLC profiling and bioautography were subsequently done for the most active extracts. Results: Among the eight plant samples, the crude extracts of four (4) of them exhibited the best antibacterial activities, whereby; Sorindeia madagascariensis leaves showed the highest activity (MIC of 0.193 ± 0.00 mg/ml) followed by S. madagascariensis roots, Mucuna stans leaves and Albizia harveyi leaves displaying MICs of 0.289 ± 0.14, 0.77 ± 0.00, and 1.54 ±0.00 mg/ml respectively. All four plant samples were active against the test bacteria, including the MRSA with S. madagascariensis leaves inhibiting it at 0.193 ± 0.00mg/ml. Tannins, phenolics, flavonoids, saponins and glycosides were the mostly detected phytochemical groups among the extracts. TLC profiles of the most active samples, revealed high proportions of polar components compared to less polar components. Subsequent bioautography suggested the activity to reside in the highly polar fractions of the plants. Conclusion: This study revealed the unpublished antibacterial potentials of the selected plants. The findings partly establish the scientific basis for ethno-medicinal applications of the plants among the indigenous of the collection sites. More importantly, it is evident that fractionation of and isolation of active molecules from these crude extracts should be done since may greatly improve the observed activities and provide lead molecules for newer antibacterial drugs. For the respective plants, the parts that were not tested in this study, specifically; the fruits, flowers, stem- and root-barks should also be explored as they may have better antibacterial activities than what this study reports.