Preliminary evidences of the direct and indirect antimicrobial activity of 12 plants used in traditional medicine in Africa

Lucy Catteau; Françoise Van Bambeke, Joëlle Quetin-Leclercq

Phytochem Rev (2015) 14:975–991


In a world of increasing resistance to current antibiotics, search of novel therapeutic options
is urgently needed. The aim of this work was to screen plant crude extracts for direct or indirect (inhibition of
resistance) antimicrobial activity. Four crude extracts from 12 plants traditionally used in Africa for the
treatment of infections were obtained by successive extraction with hexane, dichloromethane, ethyl acetate,
and methanol. All extracts were tested against Staphylococcus aureus MRSA ATCC33591 [resistant
to b-lactams by production of b-lactamases and of a modified PBP target (PBP2a)]. Direct antimicrobial
activity was tested by determination of Minimal Inhibitory Concentrations (MIC), and indirect activity,
by determining interactions between antibiotics and extracts using checkerboard titration and calculation
of Fractional Inhibitory Concentration Index (FICI; synergy: FICI B 0.5; additivity: FICI B 1). Combined
antibiotics were ampicillin (sensitive to resistance mediated by b-lactamases and PBP2a) and
oxacillin (sensitive to resistance mediated by PBP2a only). The dichloromethane extract of Vitellaria
paradoxa leaves, the methanol extracts of Vitellaria paradoxa, Cola gigantea leaves and twigs, and of
Tapinanthus bangwensis aerial parts showed direct antimicrobial activity (MIC 250–500 mg/L). The
methanol extracts of Vitellaria paradoxa and Cola gigantea leaves and twigs showed additive or synergistic
effects with oxacillin and ampicillin on MRSA ATCC33591 (FICI 0.28–1), suggesting a possible
inhibition of PBP2a. The methanol extract of Tapinanthus bangwensis aerial parts and Anchomanes
difformis roots improved the activity of ampicillin only (FICI 0.38–1), suggesting b-lactamase inhibition.
Polyphenols and particularly tannins were shown to be responsible for these last effects, at least partially for
Vitellaria paradoxa. These data need further research aiming at identifying the active compounds in these