Screening for antibacterial activity of some herbal extracts against fish and shrimp bacterial pathogens

Abstract

The usage of herbal extracts as antimicrobial agents is gaining attention in aquaculture. The current study examined the antimicrobial activity, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of four herbal plants including Cleome spinosa (CS), Cayratia trifolia (CT), Momordica charantia (MC), Premna corymbosa (PC) against fish bacterial pathogens as Aeromonas hydrophila, Edwardsiella ictaluri, Streptococcus agalactiae and shrimp bacterial pathogen as Vibrio parahaemolyticus. These herbal plants were extracted with different solvents, including hexane, ethyl acetate, chloroform, methanol and methanol hydrate. The results showed that (i) among the five types of organic extracts tested, methanol extracts were found to have maximum antibacterial activity. In which, methanol extract of P. corymbosa (PC4) showed the highest activity against E. ictaluri and S. agalactiae with the inhibition zone of 35±1.4 mm and 32±2.6 mm, respectively. In addition, the highest activity against A. hydrophila was recorded to methanol extract of C. trifolia (15.8±1.3 mm); (ii) The minimal inhibitory concentration (MIC) of methanol and chloroform extract of P. corymbosa against E. ictaluri was found to be as 1.25 and 2.5 mg/mL, respectively; MIC of methanol extract of P. corymbosa was 5 mg/ mL while MIC of chloroform extract was unable to determine. In general, methanol extract of P. corymbosa showed the greatest antibacterial activity among all herbs extracts tested.