Lipid A in outer membrane vesicles shields bacteria from polymyxins

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Drug Resistance

Background:

• Multidrug-resistant bacteria, particularly Klebsiella pneumoniae, present a significant global health threat.
• Polymyxins are last-resort antibiotics crucial for treating infections caused by resistant Gram-negative bacteria.
• Outer membrane vesicles (OMVs) are increasingly recognized for their role in bacterial communication and virulence.

Purpose of the Study:

• To investigate the role of OMVs in Klebsiella pneumoniae's resistance to polymyxin antibiotics.
• To elucidate the mechanisms by which OMVs confer protection against polymyxins.
• To explore the potential of OMVs as therapeutic targets or decoys in combating antibiotic resistance.

Main Methods:

• Comparative analysis of OMVs from polymyxin B (PB)-stressed and unstressed Klebsiella pneumoniae.
• Ex vivo and in vivo validation using precision cut lung slices (PCLS) and Galleria mellonella models.
• In vitro studies with artificial vesicles to confirm lipid A-dependent protection.
• Analysis of OMV lipid composition and binding capacity to PB.

Main Results:

• OMVs from PB-stressed K. pneumoniae exhibited enhanced protective efficacy against polymyxins due to increased vesiculation.
• OMVs acted as decoys, binding to PB and preventing its interaction with bacterial cells.
• Changes in OMV lipid composition, specifically reduced lipid A per vesicle but increased total vesicles, contributed to altered PB binding and protection.
• Artificial vesicles mimicked OMV protection, confirming the lipid A-dependent mechanism.

Conclusions:

• OMVs serve as a critical defense mechanism for K. pneumoniae against polymyxin antibiotics.
• The increased production and altered lipid composition of OMVs under antibiotic stress enhance bacterial survival.
• Targeting OMV-mediated antibiotic resistance presents a promising strategy for developing novel therapies against multidrug-resistant infections.