Significance of combination therapy between Euclea crispa (Thunb.) (leaf and stem bark) extracts and standard antibiotics against drug resistant bacteria

Abstract

This study evaluates the probable effect of combination therapy between the extracts of Euclea crispa and standard antibiotics against selected resistant strains of bacterial isolates. The crude extracts were partitioned using a solvent partitioning system. The isolates were screened via determination of minimum inhibitory concentrations (MICs) using broth micro-dilution method and the combination assessment was carried out via time-kill assay to determine the probable synergisms. The MICs by the plant extracts range from 310 to 630 μg/ml (leaf extract) and from 630 to 1250 μg/ml (stem bark extract). The MICs by erythromycin and chloramphenicol range between 31 and 250 μg/ml, while that of ampicillin is between 63 and 500 μg/ml. The range exhibited by streptomycin and tetracycline is between 8 and 250 μg/ml and 6 and 100 μg/ml respectively. Out of 130 different combination tests between the leaf extract and antibiotics, 91.5% express synergy while 8.5% are indifferent. On the other hand, 88.5% of the same number of combination tests show synergism between the stem bark extract and standard antibiotics with no record of antagonism in both cases. The leaf and stem bark extracts of E. crispa have been confirmed, in the course of this study, to possess some bioactive principles which may serve to enhance potency of the available antibiotics against multidrug resistant organisms. Thus, it indicates a source of alternative therapy in combating infectious diseases.