Bacterial resistance to antibiotics is a serious challenge to human and animal health and all efforts are being put together to resolve the menace. In this study the antibiotic resistance modifying activity of ten plants was established by determination of the minimum inhibitory concentrations (MICs) of the plant extracts, the MICs of the antibiotics alone (amoxicillin, ciprofloxacin, erythromycin and tetracycline) and the MICs of the antibiotics in the presence of sub-inhibitory concentrations of the methanol extracts of some selected medicinal plants including Clerodendron splendens, Cyperus esculentus, Duranta plumieri, Kigelia africana, Kyllinga brevifolia, Momordica charantia, Phyllanthus amarus, Pycnanthus angolensis, Secamone afzelii and Thuja occidentalis against two Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) and two Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa). The extracts were found to possess varying degree of antimicrobial activity with MICs between 4 and 50 mg/mL. It was observed that 26.9% of the plant extract-antibiotic combinations/interactions resulted in the reduction of activity of antibiotics. Almost 17% of the extract-antibiotic interactions led to the complete loss of activity of the antibiotics and 30.0% of the extract-antibiotic combinations resulted in resistance modulation. Three per cent of the extract-antibiotic combinations/interactions had antibiotics that were not active when used alone but became active in the presence of the extracts and 23.1% extract-antibiotic combinations/interactions had no modifying effect on the individual in vitro activities of the antibiotics. There is need to isolate the bioactive agents from the extracts especially those that potentiated the activity of the antibiotics.
Key words: Bacterial infections, antibiotic resistance, resistance modifying agents; medicinal plants
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