Synergism between Fructus mume and antibiotics against Vibrio harveyi based on response surface methodology

To provide basic experimental data for developing protocols to prevent and cure the disease caused by Vibrio harveyi, we collected the compound of Fructus mume water extract and antibiotics, which has synergism of antibacterial activity against V. harveyi. First, we plotted the standard curves of concentration logarithms versus inhibitory zone diameters of the test drugs, and used comprehensive combination experimental design method to screen the antibiotics which had synergism effect with F. mume water extract. Then, we applied central concentration design (CCD) with response surface methodology (RSM) to investigate the interaction among F. mume water extract and antibiotics against V. harveyi and to find their optimum combination. Results show that significant synergism existed between F. mume water extract and tetracycline, oxytetracycline, aureomycin and deoxytetracycline. RSM results indicate that the synergism between F. mume water extract and oxytetracycline contributed to the most significant effect on the antibacterial activity against V. harveyi. However, antagonism effect existed between oxytetracycline and aureomycin, and between oxytetracycline and deoxytetracycline. The optimum ratio of F. mume water extract, oxytetracycline, aureomycin and deoxytetracycline was 45∶0.12∶0.00∶0.00 (mg·mL^–1). For this optimum combination, the predictive inhibitory zone diameter was 18.54 mm. According to cup method, agar diffusion method with three replicates, the practical maximum inhibitory zone diameter was (19.03±0.07) mm, and the relative error between predictive values and actual values was 2.6%. Thus, RSM is a reliable approach to describe the relationship among test drugs and inhibitory zone diameter.