Nutritional, Phytochemicals, GC-MS and Antibacterial Activities of Aqueous Red Onion (Allium cepa) Extract against Staphylococcus aureus and Escherichia coli

Background of Study: Onion (Allium cepa) plant has been used for multiple purposes both for modern and traditional medicine. The study evaluates the atomic absorption spectroscopy (AAS), Gas chromatography–mass spectrometry (GC-MS) and antibacterial activities of aqueous red onion (Allium cepa) and azithromycin solution against Staphylococcus aureus and Escherichia coli.

Methodology: The AAS, GC-MS and phytochemical screening of the aqueous red onion (Allium cepa) extract were determined using standard procedures. Antibacterial activities were determined by agar well diffusion method. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations were determined using standard procedure.

Results: Mineral analysis shows that the minerals that were found in the red onion are: Na, Mg, Fe, Ca, K, Al and Cu. Aqueous extract of Allium cepa shows the presence of secondary metabolites like: saponin, tannins, alkaloids, flavonoids, phenolic compounds, reducing sugar, steroids etc. 56 compounds were identified using GC-MS analysis with 9, 12-octadecadienoic acid (Z,Z)- being the most abundant with peak area of 50.50% and retention time of 16.563. The results revealed that aqueous A. cepa extract with concentration of 250 mg/ml showed strong response against Staphylococcus aureus and Escherichia coli with zone of inhibition of 22.67±1.585 and 28.18±1.689 respectively. At 100 mg/ml, the onion extract exhibited weak and moderate response against both organisms. The azithromycin solution has zone of inhibition values that ranges from 9.25 ± 0.73 to 20.03 ± 1.16 mm for both organisms tested at 5.00 and 20.00 mg/mL respectively. The MIC values of the azithromycin solution and aqueous red onion extract for S. aureus and E. coli were 31.25, 31.25, 500 and 250 mg/mL while their MBC values were 62.50, 62.50, 1000.00 and 500.00 mg/ml respectively. MBC/MIC values indicate that azithromycin solution and aqueous red onion extract had bactericidal effects on both organisms tested. The red onion has potential as natural therapeutic agents and may prevent pathogenic diseases caused by Staphylococcus aureus and Escherichia coli.