Phytochemical Constituents and Antibacterial Activity of Onion (Allium cepa) Bulb and Leaf Extracts against Salmonella Typhi and Staphylococcus aureus

The widespread occurrence of drug-resistant bacteria poses a serious threat to public health despite the continued development of new antibiotics. Onion (Allium cepa) is one of the most widely cultivated species of the genus Allium and contains diverse phytochemicals with potential antimicrobial properties. This study determined the phytochemical constituents and in vitro antibacterial activities of onion bulb and leaf extracts against Salmonella Typhi and Staphylococcus aureus. Ethanolic and aqueous extracts of the bulb and leaves were prepared using cold maceration. Qualitative phytochemical screening was conducted using standard methods, while antibacterial activity was evaluated using the agar-well diffusion method at concentrations of 50, 100 and 200 mg/mL. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were also determined. Qualitative phytochemical analysis revealed the presence of flavonoids, tannins, saponins, glycosides, alkaloids and steroids, particularly in the leaf extracts. The bulb extracts generally demonstrated greater antibacterial activity than the leaf extracts. The ethanolic bulb extract at 200 mg/mL produced the largest extract-associated inhibition zone of 17.00 ± 1.41 mm against Salmonella Typhi, while the ethanolic leaf extract at the same concentration produced an inhibition zone of 11.50 ± 0.70 mm against S. aureus. The ethanolic extracts demonstrated antibacterial activity at all tested concentrations and were generally more active than the corresponding aqueous extracts. No inhibition zone was recorded for the aqueous leaf extract at 50 mg/mL against S. aureus. The aqueous leaf extract produced the highest MIC and MBC values of 50 and 100 mg/mL, respectively, against S. aureus, indicating comparatively low activity. Conversely, the ethanolic bulb extract produced the lowest MIC and MBC values of 6.25 and 12.5 mg/mL, respectively, against Salmonella Typhi. Ciprofloxacin, used as the positive control, produced inhibition zones of 35.00 ± 4.24 mm against Salmonella Typhi and 24.00 ± 2.82 mm against S. aureus. The antibacterial activity of the onion extracts may be associated with their phytochemical constituents. These findings demonstrate that ethanolic onion bulb extract possesses promising in vitro antibacterial activity, although further studies are required to identify its active compounds and establish its safety and therapeutic efficacy.

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