Antibacterial Property of Ethanolic Leaf Extract of Eucalyptus citriodora Hook on Clinical and Typed Isolates of Escherichia coli

The emergence of antibiotic resistance bacteria, necessitated the discovery and development of alternative therapy to bacterial infections. This work assessed the inhibitory property of ethanolic leaf extract of Eucalyptus citriodora against clinical isolate and E. coli ATCC 35218. Agar well diffusion test was used to determine the antibacterial activity of the extract on both isolates of E. coli. For both isolates, no zone of inhibition was observed at concentrations of the extract between 50-150 mg/ml, but at 200-500 mg/ml, there were significant (P>0.05) zones of inhibitions that ranged between 4.2 – 13.7 and 4.7 – 15.4 mm for clinical isolate and E. coli ATCC 35218 respectively. The susceptibility of both isolates to conventional antibiotics revealed ciprofloxacin (10 ug) having the highest inhibitions against both isolates (17.3 mm and 13.9 mm) respectively, followed by gentamycin (14.4 mm and 10.8 mm). The clinical isolate was resistant to amoxicillin (30 ug), while E. coli ATCC 35218 was susceptible (4.3 mm). The MIC of the extract for both isolates was 200 mg/ml while the MBCs were 300 and 350 mg/ml respectively. The inhibitory activities of the extract (15.4 mm and 13.7mm) at 500 mg/ml concentration is comparable with ciprofloxacin (17.3 mm and 13.9 mm) at a concentration of 10 µg, while that of Gentamycin at 30 µg (14.4 mm and 10.8 mm) is comparable with concentration of the extract at 450 mg/ml (13.7 mm and 11.3 mm). The zones of inhibitions produced by the extract increased with increasing concentrations. This study revealed the potency of E. citriodora ethanolic leaf extract as a future herbal candidate to treat infection caused by E. coli at high concentrations of the extract.