IN VITRO ANTIBACTERIAL ACTIVITIES OF THE BARK AND LEAF EXTRACTS OF Croton macrostachyus (Hochst. ex Delile) AND Justicia schimperiana (Hochst.ex Nees) AGAINST SOME SELECTED HUMAN PATHOGENIC BACTERIAL SPECIES

Abstract

Plants possess a wide variety of secondary metabolites which have been found to exhibit antimicrobial, antioxidant and antitumor activities. In Ethiopia, a number of plant species are traditionally used for the treatment of many diseases. Among these, Croton macrostachyus and Justicia schimperiana, which are abundantly available in many areas of the Country, are widely known for their traditional medicinal values. Therefore, this study was conducted with the objective of analyzing the profile of secondary compounds in crude extracts of the leaves and barks of the two plant species and to evaluating their antibacterial activities against some selected human pathogenic bacterial species. Extraction was done by maceration using ethanol solvent. Qualitative analysis of phytochemicals was carried out using standard protocols and phytochemicals while the quantitave analysis was done using the spectrophotometric and gravimetric methods. Furthermore, antibacterial activities of the leaf and bark extracts were determined by the disc diffusion and broth dilution methods. Results of the qualitative analysis showed that both plants have alkaloids, tannins, saponins, terpenoids and steroids in their leaves and barks. Whereas flavonoids and phlobatannins were absent in both plant leaves and barks extracts. The concentrations of the crude alkaloids (123.27mg/g, 119.57mg/g), terpenoids (118.33mg/g, 90mg/g) and phenolic constituents (3.82mg/g, 2.92mg/g) were higher in leaf extracts than in bark extracts in both C. macrostachyus and J. schimperiana, respectively, while those of the saponins (144.1mg/g and 135.33mg/g) were higher in bark extracts than in leaf extracts in both plants, respectively. Comparison between extracts and the negative control (with no inhibitory effect) showed that all types of extracts in all tested concentrations significantly inhibited the growth of all test pathogens. However, the isolates showed a sensitivity difference to extracts. When compared with the commercial antibiotic, however, all extracts at all tested concentrations (100mg/ml, 125mg/ml and 150mg/ml) had a low level of inhibitory activity against all test pathogens. The MIC required for inhibiting the growth of the test pathogens ranged from 25-100mg/ml showing variations within bacterial species and extract types. In general, the study revealed that leaf extracts showed more antibacterial activities against all tested bacteria than bark extracts. These findings suggest that C. macrostachyus and J. schimperiana leaf extracts might have great potentials in the development of antimicrobial agents useful for the treatment of diseases caused by the test pathogens provided that additional in-depth studies are made using purified active principles of the crude extracts and recent technologies.