Antimicrobial and antiprotozoal activities of twenty-four Nigerian medicinal plant extracts

Abstract

Medicinal plants exploration has become an important tool in the discovery of bioactive natural substances capable of inhibiting the mechanisms of microbial and protozoal activity. The aim of this study was to determine the antimicrobial and antiprotozoal activities of medicinal plants extracts used for the treatment of various illnesses in southwestern Nigeria.Twenty-four medicinal plant extracts were screened for antimicrobial activity against three fungal and six bacterial strains; and antiprotozoal activities against chloroquine-sensitive strains of Plasmodium falciparum (antiplasmodial assay), a culture of Leishmania donovani promastigotes and axenic amastigotes (antileishmanial activity) and two-days old culture of Trypanosoma brucei brucei (antitrypanosomal assay).Five extracts exhibited strong antifungal activity against Cryptococcus neoformans, with Ricinodendron heudelotii (Baill.) Heckel, Terminalia ivorensis A.Chev and Macaranga barteri Müll. Arg, having an IC50 of 31.73, 32.10 and 75.63 μg/mL, respectively. Ten of the extracts were active against T. brucei, with Eleusine indica displaying the most significant activity (IC50 and IC90 of 8.26 and 10.14 μg/mL). None of the extracts displayed any significant antiplasmodial and antileishmanial activities. In addition, none of the extracts displayed cytotoxicity on transformed human monocytic (THP1) cells.The study revealed that M. barteri had the broadest spectrum of activity, with activity against C. neoformans, P. aeruginosa, vancomycin resistant Enterococci faecalis (VRE) and T. brucei. M. barteri could be exploited for broad spectrum antimicrobial and antitrypanosomal activity, while Eleusine indica could be subjected to bioassay guided fractionation and isolation of antitrypanosomal constituents. This study suggests that the evaluated plants are potential sources of novel anti-infective agents.