Antimicrobial Activity of Tetradenia riparia (Hochst.) Lamiaceae, a Medicinal Plant from Tanzania

Aims: To evaluate the antibacterial activity of Tetradenia riparia crude extracts against Escherichia coli, Staphylococcus aureus and Enterococcuss faecalis. The phytochemicals that are responsible for the bioactivity were also screened.

Study Design: In vitro assay of antibacterial properties.

Place and Duration of Study: Samples were collected from Njari village at Uru North in Moshi district located in north eastern Tanzania. Extraction and phytochemical analyses were conducted at the College of Pharmacy and Nutrition, University of Saskatchewan, Saskatoon, Canada. Antimicrobial assay was carried out at Department of Microbiology, Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Canada between March 2013 and August 2013.

Methodology: Agar well diffusion test was used to determine antimicrobial activity of the plant extracts. Ethanol, methanol, hexane and distilled water were used as extracting solvents. These extracting solvents were removed by vacuo evaporator. The resulting concentrated gummy-like materials were dissolved in Dimethysulfoxide (10% DMSO). Chemical tests were used to determine the group of phytochemicals present in the sample extracts.

Results: Sensitivity testing results indicated that S. aureus was found to be more sensitive than E. coli and E. faecalis. Tetradenia riparia methanolic extracts from the root were the most active with zone of inhibition values of 29.33±0.88mm, 21.33±0.33mm and 20.0±1.0mm in diameter against S. aureus, E. faecalis and E. coli respectively. The relative inhibitory zone diameter (RIZD) was calculated. The highest percentage values of relative inhibition zone diameter of 84±5.06% (S. aureus) and 76±6.86% (E. coli) were demonstrated by T. riparia root methanolic extracts. However, T. riparia leaf and root extracts using hexane as well as leaf extracts using water did not show any antibacterial activity against E. faecalis. Root methanolic and ethanolic extracts demonstrated the minimum inhibitory concentrations ranging from 1.25mg/ml to 5.00mg/ml. Phytochemical screening of crude extracts from leaf and root of T. riparia revealed the presence of alkaloids, flavonoids, phenolics, saponins, tannins and sterols.

Conclusion: The study findings suggest likelihood of designing and developing potentially active antibacterial drug from T. riparia. Further studies should concentrate on the investigations of not only leaf but also the root part of the plant.