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

Abstract

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 fish diseases. The antimicrobial activity of methanolic and ethanolic extracts of walnut leaves and onion bulbs were evaluated against six pathogenic bacteria (Pseudomonas aeruginosa, Staphyloccocus aureus, Bacillus subtilis, Pseudomonas fluorescens, Escherichia coli, Samonella typhi) using the cupplate 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 sensitive. Bacillus subtilis was more 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/ml. The 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.

The Potential of Different Extraction Methods of Soursop (<i>Annona Muricata</i> Linn) Leaves as Antimicrobial Agents for Aquatic Animals

“…The results were in agreement with the report of Oyedeji et al (2015), Haro et al (2014) and Bello et al (2013). …”

“…Pre-poured indicator [pathogen (4 mm depth)] was overlaid with a 10 ml soft agar (0.7%) lawn of indicator culture (thus generating a potential mat for the indicating of bacteria). Wells of 10 mm diameter were cut into these agar plates using cork borer and 0.1 ml of the plant extracts was placed into each well (Bello et al, 2013). Distilled water was used as negative control while antibiotics, chloramphenicol (10 mg/mL and 20 mg/mL) were used as positive control.…”

“…A cup plate diffusion assay as described by (Bello et al, 2013) was used. Pre-poured indicator [pathogen (4 mm depth)] was overlaid with a 10 ml soft agar (0.7%) lawn of indicator culture (thus generating a potential mat for the indicating of bacteria).…”

<i>Tetracarpidium conophorum</i> (African walnut) Hutch. & Dalziel: Ethnomedicinal uses and its therapeutic activities

“…These findings contradicted similar reports of Ajaiyeoba and Fadare (2006) that methanol extract and its fractions exhibited concentration-dependent antimicrobial properties, which were carried out in the same geographical areas. Bello et al (2013b) established the potential of walnut and onion bulb extracts as antimicrobial agents for fish. It was recorded that 500 µg/mL of both extracts had the best minimum inhibitory concentration on the pathogens and could prevent the growth of microorganisms in fish feed production.…”

Phytochemical and Proximate Compositions of Tetracarpidium Conophorum [African Walnut] Seeds

“…The root of Tetracarpidium conophorum was reported to be a potential source of useful drug formulation due to the fact that it contains important bioactive components . Bello et al, [2013] Ayoolaet al, [2011] evaluated the chemical and nutritive values of Tetracarpidium conophorum seeds in their locality. As yet, not much studies has been carried out on the boiled Tetracarpidium conophorum seeds.…”