Abstract:
BACKGROUND: Multidrug resistance is a worrying cause of treatment failure in bacterial infections. The search of
bioactive constituents from medicinal plants against multidrug resistant (MDR) bacteria has significantly evolved in
the two last decades. In the present study, twenty-two compounds (three terpenoids, eleven phenolics and eight
alkaloids) isolated from three Cameroonian medicinal plants, namely Garcinia nobilis, Oricia suaveolens and
Balsamocitrus camerunensis, as well as the crude extracts were tested for their antibacterial activities against
Mycobacterium tuberculosis and Gram-negative bacteria amongst which were MDR active efflux pumps expressing
phenotypes.
METHODS: The microplate alamar blue assay (MABA) and the broth microdilution methods were used to determine
the minimal inhibitory concentrations (MIC) and minimal bactericidal concentrations (MBC) of the studied samples.
RESULTS: The results of the MIC determinations indicate that, the best crude extract was that from G. nobilis (GNB),
its inhibitory effects being noted against 12 of the 14 tested bacteria. The extract of GNB also exhibited better
anti-tuberculosis (MIC of 128 μg/ml M. tuberculosis against ATCC 27294 strain) and antibacterial (MIC of 64 μg/ml
against Escherichia coli ATCC10536) activities compared to the extracts of O. suaveolens and B. camerunensis.
Interestingly, 4-prenyl-2-(3,7-dimethyl-2,6-octadienyl)-1,3,5,8-tetrahydroxyxanthone (2), isolated from the most active
extract GNB, also showed the best activity amongst compounds, inhibiting the growth of all the fourteen tested
microorganisms. The lowest MIC value obtained with compound 2 was 8 μg/ml against M. tuberculosis ATCC 27294
and M. tuberculosis clinical MTCS2 strains. Other compounds showed selective activities with 11 of the 14 tested
bacteria being sensitive to the xanthone, morusignin I (5) and the alkaloid, kokusaginine (13).
CONCLUSIONS: The results of the present investigation provide evidence that the crude extract from G. nobilis,
O. suaveolens and B. camerunensis as well as some of their compounds, and mostly compound 2 (isolated from
G. nobilis,) could be considered as interesting natural antibacterial products.
