Synergistic antimicrobial efficacy of glabrol and colistin through micelle-based co-delivery against multidrug-resistant bacterial pathogens

Background: Widespread bacterial infection and the spread of multidrug resistance (MDR) exhibit increasing threats to the public and thus require new antibacterial strategies. Coupled with the current slow pace of antibiotic development, the use of antibiotic adjuvants to revitalize existing antibiotics offers great potential.

Purpose: We aim to explore the synergistic antimicrobial mechanism of glabrol (GLA) and colistin (COL) while developing an innovative multifunctional micelle-based drug delivery system to enhance therapeutic efficacy.

Methods: The synergy between GLA and COL was assessed through a combination of high-throughput screening and checkerboard analysis techniques. Moreover, we performed fluorescence-based assays to investigate the underlying mechanisms of action of the GLA and COL combination. We also developed a multifunctional drug delivery platform that integrates GLA and COL into co-loaded composite micelles, aimed at improving antibacterial efficacy against peritoneal sepsis and chronic bacterial wound infections caused by diverse microbial pathogens.

Results: We have discovered that natural flavonoids found in plants act synergistically with colistin against MDR bacterial infections, effectively improving its efficacy through a co-delivery strategy. The combination therapy consisting of GLA and COL exhibits enhanced antibacterial efficacy and is capable of clearing 99% of MDR Gram-positive and Gram-negative bacteria in 4 h. Mechanistic studies showed that COL increases the outer membrane permeability, which promotes the adhesion of GLA to the inner membrane, disrupting bacterial metabolism, and ultimately leading to bacterial death. Furthermore, a novel pH-responsive hydrogel system was developed and dispersed with GLA and COL co-loaded composite micelles to mitigate the selective pressure of antibiotics with fewer side effects. Lastly, such a system showed high efficacy in two animal models.

Conclusion: Our findings provide a potential therapeutic option using a co-delivery system functionalized with combination therapy, to address the prevalent infections caused by complex bacterial infections and even MDR bacterial infections.