Comparative Study of Antibacterial Properties of Emodin and Enrofloxacin Against Aeromonas hydrophila

Antibacterial properties of emodin, extracted from rhubarb, and enrofloxacin, against Aeromonas hydrophila, were assessed in this study. The minimum inhibitory concentration (MIC) values of emodin and enrofloxacin to fight A. hydrophila WJ2011BJ44 were found to be 100ug/ml and 9.375ug/ml, respectively. To understand the mechanisms of action of emodin and enrofloxcain against A. hydrophila we studied antibacterial activity, bacterial membrane permeability, and ultrastructure of A. hydrophila cells treated with emodin, enrofloxacin individually, and the combination of both. The results shown in the growth curve of A. hydrophila treated with different concentrations (from 0 MIC to 4 MIC) of emodin and enrofloxacin were similar and stable, and there was no significant difference in the growth curve of different treatment groups. There were significant differences in the K+ concentration among all treatment groups from 1 h to 8 h after incubation compared with the control. The highest K+ concentration was observed in the emodin+enrofloxacin group from 1 h to 8 h after incubation. PI fluorescence signal of untreated A. hydrophila cells and A. hydrophila cells treated with emodin, or enrofloxacin individually, or the combination of both were 0.89, 11.4, 13.98 and 18.3, respectively. The mortality of A. hydrophila cells treated with the combination of emodin and enrofloxacin was greatest compared with other groups. These results indicated that 2 MIC emodin, 2 MIC enroflxacin, and combination of 1 MIC emodin and 1 MIC enrofloxacin can inhibit the growth of A. hydrophila, increase bacterial membrane permeability, and damage cell membrane integrity. The combination of 1 MIC concentration emodin and 1 MIC concentration enrofloxacin produced the best antibacterial activity against A. hydrophila *