In vitro antibacterial activity of 40 Chinese herbal medicines against three aquatic pathogenic bacteria

Abstract

Chinese herbal medicines could be an alternative treatment for antibiotics against fish bacterial disease. The present research was carried out to investigate the antimicrobial potential of 40 herbs against <em>Edwardsiella tarda</em>, <em>Streptococcus iniae</em> and <em>Klebsiella pneumoniae</em>. Firstly, the anti-bacterial activity of forty herbal aqueous extracts (HAEs) was determined using the plate perforation method on brain heart infusion (BHI) agar. Then, effective HAEs were selected to detect the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against the pathogenic bacteria through the micro broth dilution method. Lastly, the inhibitory effects of HAEs combination were also assessed. The results showed that <em>Caesalpinia sappan</em>, <em>Fructus mume</em>, <em>Rhus chinensis</em> and <em>Punica granatum</em> could effectively inhibit all strains of the test bacteria, with the inhibitory circles in 15.00–17.00 mm diameter, MIC and MBC ranging from 31.25 to 62.50 mg/mL and 62.50 to 125.00 mg/mL, respectively. Among the compound of HAEs, the combination of <em>Fructus mume</em> + <em>Rhus chinensis</em> exhibited the most potent antibacterial efficacy against <em>E. tarda</em> and <em>S. iniae</em>, producing inhibitory circles of 19.5±0.41 mm and 19.5±0.41 mm, respectively. The MIC and MBC of this combination against <em>E. tarda</em> were 15.625 and 31.25 mg/mL, whereas, the MIC and MBC of this combination against <em>S. iniae</em> were 7.8125 and 15.625 mg/mL. The compound of <em>C. sappan</em> + <em>F. mume</em> showed the most potent antibacterial efficacy against <em>K. pneumoniae</em>, with inhibition zone diameter, MIC and MBC were 24.50±0.41 mm, 7.8125 mg/mL and 15.625 mg/mL, respectively. Overall, the results indicate that <em>C. sappan</em>, <em>F. mume</em>, <em>R. chinensis</em> and <em>P. granatum</em> showing significant potential for inhibiting pathogens, and their combinations could be a potential alternative to treat the aquatic bacteria diseases.