Full Length Research Paper

Studies on the in vitro time kill assessment of crude acetone and aqueous extracts of Helichrysum pedunculatum leaves

O.A. Aiyegoro¹, A.J. Afolayan² and A.I. Okoh¹*

¹Applied and Environmental Microbiology Research Group (AEMREG), Department of Biochemistry and Microbiology, University of Fort Hare, Alice 5700, Private Bag X1314, South Africa.

²Phytomedicine Group, Department of Botany, University of Fort Hare, Alice 5700, Private Bag X1314, South Africa.

*Corresponding author. E-mail: aokoh@ufh.ac.za. Tel: +27-822-249-760. Fax: +27- 866-286-824.

Accepted 29 August, 2008

Helichrysum pedunculatum is used in folklore remedies to dress wound acquired after circumcision rite. This led to the study of in vitro antibacterial activities of this medicinal plant. Using standard microbiological procedures, six bacteria species made up of four gram positive and two gram negative bacteria were screened for susceptibility to crude acetone and aqueous extracts of this plant. The minimum inhibitory concentrations (MICs) of the acetone extract against the susceptible bacteria was 5.0 mg/ml while that of the aqueous extract ranged between 0.5 - 35 mg/ml. Average log reduction in viable cell count in time kill assay of the acetone extract ranged between 0.64 Log₁₀ and 5.99 Log₁₀ cfu/ml after 6 h of interaction, and between 5.99 Log₁₀ and 6.06 Log₁₀ cfu/ml after 12 h interaction in 1 × MIC and 2 × MIC, and between 0.10 Log₁₀ to 0.33 Log₁₀ cfu/ml after 6 h of interaction, and 0.23 Log₁₀ and 0.56 Log₁₀ cfu/ml after 12 h interaction in 1 × MIC and 2 × MIC for the aqueous extract. The effect of the aqueous extract was only bacteriostatic on both reference and environmental strains and the clinical isolates were outrightly resistant to this extract (not reported here). This is worrisome and this could be one reason why, there is an incidence of high death rate resulting from circumcision wounds infection even after treating such wounds with H. pedunculatum leaf. Perhaps the plant could be of more relevance in combination therapy and a source of resistance modifying principles which is the subject of on going studies in our group.

Key words: Helichrysum pedunculatum, minimum inhibitory concentration, log reduction, time-kill, bacteriostatic, bactericidal, antibacterial.