In vitro antilisterial properties of crude aqueous and nhexane extracts of the husk of Cocos nucifera

Abstract

The in vitro antilisterial activities and time kill regimes of crude aqueous and n-hexane extracts of the husk fiber of Cocos nucifera were assessed. The aqueous extracts were active against 29 of the 37 test Listeria isolates while the n-hexane extracts were active against 30. The minimum inhibitory concentrations (MICs) of all the susceptible bacteria ranged between 0.6 and 2.5 mg/ml for the aqueous fraction and between 0.6 and 5.0 mg/ml for the n-hexane extract. The average log reduction in viable cell count in the time kill assay ranged between 0.32 Log₁₀ and 3.2 Log₁₀ cfu/ml after 4 h of interaction, and between 2.6 Log₁₀ and 4.8 Log₁₀ cfu/ml after 8 h interaction in 1 × MIC and 2 × MIC (aqueous extract); and between 2.8 Log₁₀ and 4.8 Log₁₀ cfu/ml after 4 h of interaction, and 3.5 Log₁₀ to 6.2 Log₁₀ cfu/ml after 8 h interaction in 1 × MIC and 2 × MIC for the n-hexane extract. The extract was bactericidal against one of the test bacteria at 1 × MIC and against three of the test bacteria at 2 × MIC for the 8 h interaction period for the aqueous extract, while for the n-Hexane fraction; the extract was bactericidal against all the five test bacteria at both MICs after the 8 h interaction period. We suggested that the crude aqueous and n-hexane extracts of the husk of C. nucifera could be bacteriostatic or bactericidal depending on the time of exposure and concentration.

Key words: Cocos nucifera, n-hexane extract, aqueous extract, minimum inhibitory concentration, time-kill.