African Journal of
Microbiology Research

  • Abbreviation: Afr. J. Microbiol. Res.
  • Language: English
  • ISSN: 1996-0808
  • DOI: 10.5897/AJMR
  • Start Year: 2007
  • Published Articles: 5233

Full Length Research Paper

Potentials of walnut (Tetracarpidium conophorum Mull. Arg) leaf and onion (Allium cepa Linn) bulb extracts as antimicrobial agents for fish

Bello O. S.1*, Olaifa F. E.1, Emikpe B. O.2 and Ogunbanwo S. T.3
1Department of Aquaculture and Fisheries Management, University of Ibadan, Nigeria. 2Department of Veterinary Pathology, University of Ibadan, Nigeria. 3Department of Microbiology, University of Ibadan, Nigeria.
Email: [email protected]

  •  Accepted: 26 April 2013
  •  Published: 07 May 2013


The development of antibiotic-resistant pathogens due to the indiscriminate use of antibiotics has led to advocacy for the use of natural products in the treatment of fishdiseases. The antimicrobial activity of methanolic and ethanolic extracts of walnut leaves and onion bulbs were evaluated against six pathogenic bacteria (Pseudomonas aeruginosa, Staphyloccocus aureusBacillus subtilis, Pseudomonas fluorescens,Escherichia coliSamonella typhi) using the cup – plate method. Minimum Inhibitory Concentration (MIC) was determined using standard methods. Data were analysed using descriptive statistics. Onion bulbs and walnut leaves were also screened for secondary metabolites and this indicated the presence of saponins, tannin, alkaloids, cyanogenic glycosides and flavonoids; while anthraquinones were not detected in both plants. The zone of inhibition varied with the bacteria and type of extract. The average diameter of inhibition zones was 10 ± 0.00 and 9 ± 0.02 mm for methanolic and ethanolic extracts of walnut leaves and onion bulbs, respectively. Staphylococcus aureus, B. subtilis and P. aeruginosa were most sensitive to the extracts. However, S. aureus was more sensitive to the extracts of walnut leaves and S. typhi was the least sensitiveBacillus subtilis wasmore sensitive to the extracts of onion compared to E. coli which was the least sensitive. Minimum inhibitory concentration of walnut leaves and onion bulbs extracts on the bacteria tested were both 500 µg/mlThe results indicated that walnut leaves and onion bulbs had antibacterial activity on the tested organisms and showed their prospects for their use in the treatment of fish diseases.


Key words: Antibacterial activity, onion bulb extract, walnut leaf extract, fish diseases.