Abstract:
The rise in antibiotic resistance has resulted in a decreasing number of fully active antimicrobial agents
available to treat infections by multi-drug resistant (MDR) bacteria. This has necessitated a search for new
antimicrobial agents. Herbal remedies may offer novel treatment options which elicit little or no transferred
resistance if used in optimal concentrations. This study evaluated the antimicrobial properties of ten plants
traditionally used as herbal remedies against 27 multi-drug resistant Gram-negative bacterial isolates. The
herbal extracts were obtained through extraction with organic (methanol) and inorganic (water) solvents.
Susceptibility of the test strains to conventional antibiotics was determined by the disc diffusion technique.
Determination of the Minimum Inhibitory Concentrations (MIC) and the sub-lethal concentrations of the most
effective extracts against the MDR strains was done by broth inoculation followed by colony count method.
The effect of sub-lethal extract concentrations was done by a method modified from McMahon et al. (2007).
Out of the ten plants, only Warbugia ugandensis was active against the MDR strains and its efficacy was
significantly different from that of other plant extracts such as Terminalia brownii, Azaridachta indica,
Clausena anisata and Strychnos henningsii (p<0.001). The root and bark methanol extracts from W.
ugandensis were the most effective with an MIC of 42 μg/ml. Susceptibility of test strains to conventional
antibiotics was not significantly different before and after habituation to sub-optimal extract concentration
(p>0.005). Methanol extracts from the root and bark of W. ugandensis provide potential sources of effective
antimicrobial compounds for further development of alternative safe antimicrobial products in form of
chemotherapeutic agents or antiseptics. The optimization and standardization of operation procedures and
methods of analysing the efficacy of herbal extracts demands serious consideration.
