Antibacterial activity of Litsea cubeba (Lauraceae, May Chang) and its effects on the biological response of common carp Cyprinus carpio challenged with Aeromonas hydrophila
Aims: The aims of this study were to characterize the antibacterial activity and the chemotype of Litsea cubeba leaf essential oil (EO) harvested in North Vietnam and to investigate the biological effects induced by the leaf powder on growth, nonspecific immunity and survival of common carp (Cyprinus carpio) challenged with Aeromonas hydrophila. Methods and Results: The EO showed the prevalence of linalool (95%, n=5). It was bactericidal against the majority of tested strains, with Minimum Inhibitory Concentrations ranging from 0.72 to 2.89 mg ml-1 (A. hydrophila, Edwarsiella tarda, Vibrio furnissii, Vibrio parahaemolyticus, Streptococcus garvieae, Escherichia coli, Salmonella Typhimurium). The fish was fed with 0% (control), 2%, 4%, and 8% leaf powder supplementation diets during 21 days. Nonspecific immunity parameters (lysozyme, haemolytic and bactericidal activities of plasma) were assessed 21 days after feeding period and before the experimental infection. Weight Gain, Specific Growth Rate and Feed Conversion Ratio were improved by supplementation of L. cubeba in a dose related manner; and a significant difference appeared at the highest dose (8%) when compared to the control. The increase of plasma lysozyme was significant for all treated groups. Haemolysis activity was higher for the groups fed with 4% and 8% plant powder. Antibacterial activity increased significantly for the 8% dose only. Conclusions: L. cubeba leaf powder increased nonspecific immunity of carps in dose related manner. After infection with A. hydrophila, survivals of fish fed with 4% and 8% L. cubeba doses were significantly higher than those fed with 2% dose and the control.