In vitro assessment of antibacterial activity of crude extracts of onion (Allium cepa L.) and shallot (Allium aescalonicum L.) on isolates of Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), and Salmonella typhi (ATCC 19430)

Abstract

Antibacterial activity of crude extracts of two Allium species namely Allium cepa Linn (onion) and Allium aescalonicum Linn (shallot) cultivated in Ghana was investigated on isolates of Escherichia coli (ATCC 25922), Staphylococcus aureus (ATCC 25923), and Salmonella typhi (ATCC 19430) by the agar well diffusion method. Broth cultures of the test bacterial isolates were standardised to 0.5 McFarland (1.0 × 106 cfu/ml) and seeded on nutrient agar. Crude extracts of the onions and shallots were prepared from samples bought from the market. 75µl of undiluted and diluted crude extracts were introduced into corresponding agar wells and incubated at room temperature (approximately 37 °C) for susceptibility test. 15µg/mL of Ciprofloxacin was set as control. After 24 hours of incubation, zones of inhibition were measured and recorded in millimetres. The undiluted extracts exhibited greater inhibitory activity on the test organisms than the diluted extracts. Salmonella typhi was observed to be susceptible to the crude extracts though resistant to ciprofloxacin. Diluting crude extracts of both onion and shallot beyond 1:2 dilution had no antibacterial action on the isolates. Further research is recommended on the pharmacokinetics of the active components in the crude extracts. Eating raw onions and shallots should be encouraged.