In Vitro Antimicrobial Activity and Toxicity of Selected Medicinal Plants Used to Manage Bacterial Gastroenteritis in Meru County, Kenya
Maithulia, Stephen Mugambi
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Herbal drugs have been used in management of bacteria causing bacterial gastroenteritis without scientific evaluation on their antimicrobial activity and toxicity. This research was designated to evaluate in vitro activities of methanol extracts of Aloe deserti, Zanthoxylum chalybeum and Zanthoxylum usambarense and assess their possible toxicity using the mice models. The crude extracts were evaluated on their activities against Gram-negative bacteria (Escherichia coli ATCC 25922, Salmonella typhi ATCC 19430 and Shigella dysenteriae ATCC 13313) and Gram-positive bacteria (Bacillus cereus ATCC 10876, Bacillus subtilis ATCC 6633, Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29912) using the Disk Diffusion Method, Minimum Inhibitory Concentration (MICs), Minimum Bactericidal Concentration (MBCs) and Time Kill studies. Methanol extracts of Z. usambarense showed strong susceptibility against five tested bacteria (B. cereus ATCC 10876, B. subtilis ATCC 6633, S. aureus ATCC 29213, E. faecalis ATCC 29912, E. coli ATCC 25922) and the other two bacteria had weak susceptibility (S. typhi ATCC 19430, S. dysenteriae ATCC 13313). Methanol extract of Z. chalybeum was active only to two Gram-positive bacteria (B. subtilis ATCC6633, B. cereus ATCC10876). Aloe deserti methanol extracts were completely inactive against all the tested bacteria. Only Z. usambarense extracts was evaluated on MICs, MBCs and Time Kill because of its high bioactivities. The MICs results gave good low MICs of 12.5mg/ml and 50mg/ml. The MBCs were as low as 12.5mg/ml while the highest being 100mg/ml. MBC/MIC values indicated good activities of 1.0 (bactericidal activities). Time Kill Assay was determined by plate count technique and analyzed by % kill or growth of viable colonies. The herbal drug displayed bacteriostatic activities toward test bacteria (B. cereus ATCC 10876, B. subtilis ATCC 6633) at 0.5×MIC concentration after 24 hr exposure. Methanol extract of Z. usambarense displayed time dependent killing kinetics that ranged between100 and 96 cfu/ml for S. aureus ATCC 29213, 100 and 98 cfu/ml for E. feacalis ATCC 29912, and 131 and 96 cfu/ml for E. coli ATCC 25922. The herbal drug was rapidly bactericidal at 1×MIC concentration achieving 99.9 % elimination of B. cereus ATCC 10876 and B. subtilis ATCC 6633 and at 2×MIC killing completely (99.9 %) B. cereus ATCC 10876, B. subtilis ATCC 6633 and S. aureus ATCC 29213 after 8 hr exposure except E. feacalis ATCC 29912 and E. coli ATCC 25922 displaying bacteriostatic activities. Toxicity in mice was assessed by administering extracts orally and intraperitoneally at 450, 670 and 1000 mg/kg body weight after 4 weeks by noting changes in behavior, body and organ weight, hematological and biochemical parameters. The reduced growth rate, organ weight and increased levels hematological and biochemical parameters indicated slight toxicity of plant extracts. The same dose in both routes increased the liver and spleen, and decreased the testis weight, and increased the hemoglobin levels, packed cell volume and platelets; increased the activity of aspartate aminotransferase and lactate dehydrogenase, and decreased the activity of alkaline phosphatase, gamma-glut amyl transferase, and creatine kinase slightly injured the spleen, kidney and liver organs. Toxicity studies confirmed the safety of plant extracts in both routes. The phytochemical analysis results showed the presence of alkaloids, tannins, glycosides, flavonoids, terpenoids and anthraquinones. Analysis of elements such as Mg, K, Ca, Mn, Fe, Zn, Pb, Cr, Sr, Cu, As, V, and Hg were done using AAS and results showed presence of metals at varying concentrations. The measured mineral did not cause toxicity because their levels were below the recommended daily allowance. In conclusion, the observed antimicrobial activity and slight toxicity could be associated with phytochemicals and minerals present in extracts. Results from this work recommend use of Z. usambarense extract as phyto-medicine to manage bacterial gastroenteritis. Further studies of Z. usambarense are recommended using higher animals.