Synergistic Antibacterial Effects of Polygonatum sibiricum Red. with Oxytetracycline on Vibrio parahaemolyticus

In this paper, Polygonatum sibiricum Red. and 8 kinds of aquatic antibiotics were used to inhibit Vibrio parahaemolyticus, the main pathogen of acute hepatopancreas necrosis disease (AHPND) in shrimp culture. The minimum inhibitory concentration (MIC) of P.sibiricum Red. and antibiotics were determined by chessboard method. The effects of Polygonatum on the membrane conductivity, membrane potential and survival rate of bacteria were studied. The effects of Polygonatum sibiricum Red. on the expression of efflux pump related genes were studied by RT-PCR. The results showed that the combination of P. sibiricum Red. and oxytetracycline had the best synergistic antibacterial effect with the optimum combination of 1/8 MIC P. sibiricum Red.+1/4 MIC oxytetracycline and the FIC of 0.38. The synergy turned into additive or even irrelevant effects in the presence of CCCP. Conductivity, membrane potential and propidium iodide staining proved that P. sibiricum Red. could destroy the cell membrane of V. parahaemolyticus, improving its permeability, leading to the depolarization of the cell membrane and the disappearance of proton gradient on both sides of the membrane. P. sibiricum Red. significantly inhibited the expression of five outer membrane proteins, five reverse synergistic transporters and 11 RND efflux transporters of V.parahaemolyticus, of which vpa0096 (OmpW) was down-regulated by 497.51 times, while vp0425 (TolC), vp2072 (Na⁺/H⁺), vp2665 (Na⁺/Ca²⁺ exchanger), vp1092, vp0911, vp1178, vpa0344, and vpa0809 were down-regulated by 27.03, 73.53, 55.56, 100.00, 35.71, 37.74, 49.02, and 56.18 times, respectively. P. sibiricum Red. reduced the activities of malate dehydrogenase (MDH) and succinate dehydrogenase (SDH) of TCA cycle, thereby inhibiting the TCA cycle of V.parahaemolyticus. Oxytetracycline is one of the substrates of vp0425 (TolC). Polygonatum sibiricum Red. is a natural efflux pump inhibitor, which can keep oxytetracycline in cells and improve the antibacterial effect of oxytetracycline. The synergistic effect of Polygonatum sibiricum Red. and oxytetracycline on vibriosis in aquaculture can greatly reduce the concentration of oxytetracycline, residual risk and the emergence of drug-resistant Vibrio, thus promoting the healthy development of aquaculture.