Yao Xinyu,Shu Yang,Xu Lei,Wei Lijuan,Cui Minhe,Li Li,Zhang Peng,Fang Tianqi
Colistin is recognized as the “last line of defense” for the treatment of carbapenemase-producing “super-resistant” bacteria. However, the treatment of clinical bacterial infections has become more challenging due to the widespread prevalence of the novel resistance gene mcr-1 in multidrug-resistant pathogens. Currently, the use of natural compounds as novel adjuvants to colistin treatment is a safe, feasible, and promising approach compared to the high cost and unpredictability of developing novel antimicrobial drugs. Here, we identified a potential MCR-1 inhibitor, ursodeoxycholic acid, that may be used to treat infections caused by MCR-1-positive drug-resistant bacteria. In this study, checkerboard minimum inhibitory concentration assays demonstrated that ursodeoxycholic acid could reduce the MICs of colistin-resistant strains 4–64 times. Furthermore, a time-kill curve analysis, combined with disk diffusion testing and live/dead bacterial staining, demonstrated that ursodeoxycholic acid could effectively enhance the antibacterial activity of colistin, and when the concentration of ursodeoxycholic acid was lower than 512 μg/ml, it did not affect the normal growth of bacteria; thus, ursodeoxycholic acid imparts less selective pressure on bacteria and did not easily induce the emergence of drug resistance. In addition, through potential target prediction, molecular docking, RT-PCR analysis, membrane permeability detection, and scanning electron microscopy analysis, we demonstrated that ursodeoxycholic acid can form a complex with MCR-1, suggesting that UDCA may affect the activity of MCR-1. In addition, ursodeoxycholic acid combined with colistin was able to alter the electronegativity and permeability of the bacterial membrane, thereby disrupting the structural integrity of the bacterial membranes and significantly enhancing membrane damage–associated colistin activity. In summary, our findings indicate that the colistin/ursodeoxycholic acid combination may be a promising alternative approach for treating MCR-1-positive bacterial infections. Graphical Abstract
Bacterial drug resistance is becoming an increasingly serious problem, and the development of antibacterial synergists is urgently needed. Combining existing antibiotics with promising nonantibiotic agents is one strategy that has been shown to be effective at overcoming the widespread emergence of antibiotic-resistant pathogens. In this study, we investigated the antibacterial activities and mechanism of naringenin (NG) combined with amikacin (AMK) against multidrug-resistantEscherichia coli(E. coli). We first measured the fractional inhibitory concentration (FIC) of NG combined with antibiotics via the checkerboard method. The results indicated that the combination of NG and AMK had a synergistic effect onE. coliATCC 25922 andE. coliC7F3. In addition, this synergistic effect was verified by time-kill assays. Moreover, scanning electron microscopy (SEM) was used to observe cell morphology. The results showed that the cell wall ofE. coliwas destroyed. Furthermore, we assessed the leakage of alkaline phosphatase (AKP), K+, and protein. The extracellular AKP activity increased after the combinational group of 1/2MIC NG and 1/2MIC AMK, suggesting an impairment in cell wall permeability. An increase in the leakage of intracellular K+and protein indicated an increase in cell inner membrane permeability. These results revealed that NG and AMK inhibitedE. coliby damaging cell walls and membranes. In addition, PI uptake rapidly increased after treatment with NG and AMK. Confocal laser scanning microscopy (CLSM) revealed that NG caused cell wall and cell membrane damage inE. coli. In summary, our results provide a new strategy for responding to the development ofE. colidrug resistance.
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