The antibacterial activity of the crude leaf extracts of Eucalyptus camaldulensis were determined using the agar well diffusion method against clinical isolates of Escherichia coli, Staphylococcus aureus, Salmonella typhi, Proteus mirabilis andKlebsiella pneumoniae. At an extract concentration of 50 mg/ml, the growths of all the pathogenic bacteria were arrested, though to varying degrees. The least activity in terms of zones of growth inhibition was shown by aqueous extract against E. coli (7 mm), K. pneumoniae (9 mm), P. mirabilis (13 mm), S. typhi (12 mm) and S. aureus (12 mm) while the highest was demonstrated by the acetone extract, with a recorded zone diameter for E. coli (12 mm), K. pneumoniae (13 mm), S. typhyi (14 mm), P. mirabilis (15 mm) and S. aureus (14 mm). The effects of pH and temperature on the efficacy of the crude drug extracts were also determined. The effectiveness of the extracts were more pronounced under alkaline conditions and lower temperatures. Minimum inhibitory concentration (MIC) values ranged from 6.25 - 50 mg/ml and minimum bactericidal concentration (MBC) values ranged from 6.25 - 100 mg/ml. The ability of the crude extracts to inhibit the growth of the bacteria used in this study is an indication that the leaves of E. camaldulensis can be used as a source for the development and formulation of antibacterial drugs, thus justifying the use of the leaves in herbal medicines to treat a variety of infectious conditions.
Key words: Eucalyptus camaldulensis, maceration, agar well diffusion, efficacy, alkaline, antimicrobial activity.
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