In vitro inhibitory activity of Chinese leek extract against Campylobacter species

Three aqueous extracts of dietary materials of Chinese leek (leek flower stem, soft leek and green leek) and two other reference extracts of Allium plants were used to investigate the antibacterial effects against Campylobacter jejuni and Campylobacter coli. All the tested strains of Campylobacter species were isolated from chickens. The minimum concentration of aqueous leek extracts (ALEs) required to inhibit the bacterial growth was 2.0 mg/ml. Among the plant extracts tested, ALEs shared the lowest value of minimum inhibitory concentration (MIC), and soft leek significantly demonstrated the strongest inhibitory activities (P<0.05). All the Allium plants tested shared similar characteristics of heat and pH susceptibility. Heat treatment (>75 °C) of the extracts reduced the inhibitory activity. The boiled ALEs revealed significant loss of inhibition (P<0.05), but they retained some inhibitory effect. The antibacterial activities of the ALEs were stable between pH 2.0 and 8.0, while the effects were significantly decreased (P<0.05) when pH of the ALEs were adjusted to 1.0 or 9.0 above. The results indicated that the antibacterial activities of the ALEs against Campylobacter species were more effective than that of aqueous garlic extract.