Antibacterial mechanism of IBG against MDR bacteria. (A) Dynamic curves of the outer membrane probed with NPN in E. coli ATCC 25922 treated with IBG (10 μg/mL), colistin (0.12 μg/mL), and both together. The fluorescence was detected with excitation and emission wavelengths of 350 nm and 420 nm. (B) The ΔpH after treatment with different concentrations of IBG (from 0 to 10× MIC) was determined in S. aureus ATCC 29213. The means for three biological replicates are shown, and error bars represent the SD. (C) Levels of intracellular ATP in S. aureus ATCC 29213 after treatment of IBG. Nonparametric one-way analysis of variance (ANOVA) was used to calculate P values (*, P < 0.05; **, P < 0.01). (D) Accumulation of ROS in E. coli ATCC 25922 treated with IBG with or without 0.12 μg/mL colistin. (E) IBG inhibits the transcript level of mcr-1 in E. coli SHP45 determined by qRT-PCR. All data are means and SD, and significance was determined by nonparametric one-way ANOVA (**, P < 0.01). (F) Scheme of mechanisms of action of IBG in Gram-positive and Gram-negative bacteria.