In vitro antibacterial effect of berberine hydrochloride and enrofloxacin to fish pathogenic bacteria

Berberine the main antibacterial substance in the rhizome of Coptis chinensis Franch, is used as an antimicrobial agent for a long time. This study was carried out to investigate the potential of berberine alone or in combination with enrofloxacin against six common fish pathogens for use in fish disease management in aquaculture. The minimum inhibitory concentrations (MICs) of berberine hydrochloride against Aeromonas hydrophila, Pseudomonas fluorescens, Vibrio vulnificus, Edwardsiella ictaluri, Escherichia coli and Streptococcus agalactiae were determined and to be >500, >500, >500, 300, 400 and 100 μg mL^?1 respectively. The minimal bactericidal concentrations (MBCs) of berberine hydrochloride to E. coli, E. ictaluri and S. agalactiae were 300–500 μg mL^?1. In combination with enrofloxacin, the MICs and MBCs of berberine hydrochloride significantly decreased against E. coli and E. ictaluri but not against Streptococcus dysgalactiae. These results demonstrated that the berberine hydrochloride enhanced the bactericidal effect of enrofloxacin and vice versa. The synergistic bactericidal effect of berberine hydrochloride and enrofloxacin suggest its potential use in fish disease management in aquaculture. This is the first study on the inhibitory effect of berberine hydrochloride against fish pathogenic bacteria.