Antibacterial Potential and Safety Level of Euphorbia tirucalli and Vernonia glabra Commonly used by Residents in Iringa, Tanzania

This study was conducted to evaluate the antibacterial potential of Euphorbia tirucalli L. and Vernonia glabra (Steetz) Vatke and their safety level.  The plants were obtained from Kiwere ward in the Iringa district, prepared and extracted in aqueous and ethanol solvents. The E. tirucalli and V. glabra plant extracts were studied for their antimicrobial activities against E. coli isolates and E. coli ATCC 25922 using the agar well diffusion method. Minimum inhibitory and bactericidal concentrations (MIC and MBC) were determined. Among the tested plant extracts, the ethanol extracts of V. glabra showed the highest activity against E. coli isolates and E. coli 25922 with a mean inhibition zone of 17.909±0.3297 and 22.5 ± 0.500 respectively. Furthermore, on MIC and MBC, the ethanol extracts of V. glabra had a better activity with the values ranging from 1.25-2.5 mg/ml and 2.5-5 mg/ml respectively compared to other plant extracts. Phytochemical screening revealed the extract’s presence of alkaloids, flavonoids, tannins, saponins, triterpenes and steroids. The brine shrimp lethality test showed that the aqueous extract of E. tirucalli was non-toxic with LC50 of 1007 µg/mL, while ethanol extract of E. tirucalli, aqueous extract of V. glabra and ethanol extract of V. glabra were less toxic with LC50 values of 589, 507 and 658 µg/mL respectively.  These results indicate that the plant extracts have bioactive constituents that could be accounted for their pharmacological properties. Furthermore, these results proved the claim of indigenous people in the study area on the effectiveness and safety of the plants and supported the use of these plant species in traditional medicine.