Antibacterial activity of edible herbs against fish pathogenic bacteria

Five selected herbs, betel vine (Piper betle), betel leaves (Piper sarmentosum roxb), turmeric (Curcuma longa), Indian pennywort (Centella asiatica) and kaffir lime (Citrus hystrix) were examined for their antibacterial properties against Gram positive bacteria namely, Staphylococcus aureus, Streptococcus agalactiae and Streptococcus aginosus and Gram negative bacteria namely, Vibrio parahaemolyticus, Vibrio vulnificus, Citrobacter freundii, Escherichia coli, Edwardsiella tarda and Aeromonas hydrophila. Among all herb extracts, only betel vine, turmeric and kaffir lime possessed antibacterial activities against fish pathogenic bacteria. Extracts of betel vine showed highest antibacterial activity in both form of methanol and aqueous extracts. The broadest antibacterial activity was methanol extracts which inhibited almost all bacterial species such as V. parahaemolyticus, E. coli, E. tarda, A. hydrophila, S. aureus and S. aginosus at 200 mg/ml. In determination of minimum inhibitory concentration (MIC), methanol extracts of piper betle required 1.56 mg/ml to inhibit the growth of both V. parahaemolyticus and A. hydrophila. The effect of temperature on antibacterial activity indicated the herbs tested were heat stable ranging from 37˚C to 105˚C.