Antibacterial efficacy of the butanol-soluble portion of de-pigmented methanol leaf extract of Strychnos spinosa

Abstract

Background: The presence of pigments, such as chlorophyll, in plant extract, has reportedly masked or interfered with the antibacterial property of some extracts. This work was designed to compare the antibacterial efficacies of both the pigmented and de-pigmented extracts of the leaves of Strychnos spinosa. Methods: De-pigmentation of extracts, phytochemical screening of extracts and their partitioned-soluble portions were carried out using standard methods. The butanol-soluble portion was further purified to obtain fractions and sub-fractions. All extracts/portions/fractions/sub-fractions were tested against a range of Gram-positive and Gram-negative bacteria strains in comparison with chloramphenicol using the agar-well diffusion method. Results: The de-pigmented crude methanol extract (Mss-C) revealed stronger presence of phenolic compounds than the pigmented crude methanol extract (Mss). In vitro antibacterial assay of Mss-C and its butanol-soluble portion (Mss-Cb) revealed appreciable broad spectrum inhibitory activities against Gram-positive Staphylococcus aureus and Bacillus subtilis, and Gram-negative Pseudomonas aeruginosa, better than that exhibited by chloramphenicol. Mss-C (21.3 mm +/- 1.00) and Mss-Cb (25.1 +/- 0.71) displayed significant inhibitory activities against Staph aureus than chloramphenicol (16.1 mm +/- 1.05). Fractions and sub-fractions obtained from Mss-Cb displayed lesser inhibitory activities than Mss-Cb, while a combination of the two most active fractions of Mss-Cb gave rise to a mixture that produced a stronger broad spectrum inhibitory activity than Mss-Cb. Conclusion: The above findings suggest that the butanol-soluble portion of the de-pigmented methanol extract of the leaves of Strychnos spinosa possess significant antibacterial activity.