Full Length Research Paper

In vitro time kill assessment of crude methanol extract of Helichrysum pedunculatum leaves

Aiyegoro, O. A.¹, Afolayan, A. J.² and Okoh, A. I.¹*

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. Email: aokoh@ufh.ac.za.

Accepted 26 February, 2008

The in vitro antibacterial activities and time kill regimes of crude methanol extract of Helichrysum pedunculatum was assessed using standard microbiological procedures. The experiment was conducted against a panel of bacterial species made up of clinical, environmental and reference strains. The extract was active against eleven of the twenty-one bacteria tested at a concentration of 10 mg/ml. Minimum Inhibitory Concentration (MIC) values for all the susceptible bacteria ranged between 0.1 – 5.0 mg/ml. The average log reduction in viable cell count in time kill assay ranged between 0.17 Log₁₀ to 6.37 Log₁₀ cfu/ml after 6 h of interaction, and between 0.14 Log₁₀ and 6.99 Log₁₀ cfu/ml after 12 h interaction in 1×MIC and 2×MIC of the extract. The extract was bactericidal against 8 of the test bacteria at 1×MIC and against 9 of the test bacteria at 2×MIC from 12 h interaction period. At both MIC levels, the extract was bactericidal to all the reference strains and four of the six environmental strains at both MIC levels after 12 h of interaction. Also the extract was bactericidal to four of the six environmental strains at both MIC levels after 12 h of interaction and bacteriostatic during the first 6 h of interaction. Inhibitory levels of crude methanol extract of H. pedunculatum could be bacteriostatic or bactericidal independent of Gram’s characteristic.

Key words: Helichrysum pedunculatum, methanol extract, MIC, time-kill.