Lipidomic Analysis of the Outer Membrane Vesicles from Paired Polymyxin-Susceptible and -Resistant Klebsiella pneumoniae Clinical Isolates

Abstract

Gram-negative bacteria produce outer membrane vesicles (OMVs) as delivery vehicles for nefarious bacterial cargo such as virulence factors, which are antibiotic resistance determinants. This study aimed to investigate the impact of polymyxin B treatment on the OMV lipidome from paired polymyxin-susceptible and -resistant Klebsiella pneumoniae isolates. K. pneumoniae ATCC 700721 was employed as a reference strain in addition to two clinical strains, K. pneumoniae FADDI-KP069 and K. pneumoniae BM3. Polymyxin B treatment of the polymyxin-susceptible strains resulted in a marked reduction in the glycerophospholipid, fatty acid, lysoglycerophosphate and sphingolipid content of their OMVs. Conversely, the polymyxin-resistant strains expressed OMVs richer in all of these lipid species, both intrinsically and increasingly under polymyxin treatment. The average diameter of the OMVs derived from the K. pneumoniae ATCC 700721 polymyxin-susceptible isolate, measured by dynamic light scattering measurements, was ~90.6 nm, whereas the average diameter of the OMVs isolated from the paired polymyxin-resistant isolate was ~141 nm. Polymyxin B treatment (2 mg/L) of the K. pneumoniae ATCC 700721 cells resulted in the production of OMVs with a larger average particle size in both the susceptible (average diameter ~124 nm) and resistant (average diameter ~154 nm) strains. In light of the above, we hypothesize that outer membrane remodelling associated with polymyxin resistance in K. pneumoniae may involve fortifying the membrane structure with increased glycerophospholipids, fatty acids, lysoglycerophosphates and sphingolipids. Putatively, these changes serve to make the outer membrane and OMVs more impervious to polymyxin attack.

Cracking Open Bacterial Membrane Vesicles

“…The authors hypothesized that these cells may use OMV formation as a way to selectively remove environmentally disadvantageous LPS species from the outer membrane under certain conditions. Another study showed that the size and lipid composition of Klebsiella pneumoniae OMVs was altered after polymyxin treatment, suggesting that the lipid composition of OMVs reflects the outer membrane remodeling associated with cell envelope stress induced by polymyxin (Jasim et al, 2018). In contrast, several studies have suggested a mechanism in which certain proteins determine the MV composition.…”

Fitness of Outer Membrane Vesicles From Komagataeibacter intermedius Is Altered Under the Impact of Simulated Mars-like Stressors Outside the International Space Station

“…The core lipids of K. intermedius, which serve as the framework for fully mature membrane lipids, are PLs, triglycerides, FAs, and sterols. Typical membrane parameters adversely affected by environmental challenges are permeability and fluidity, which, in turn, affect the function and mobility of membrane proteins, diffusion of nutrients, and energy sources (Rowlett et al, 2017;Siliakus et al, 2017;Jasim et al, 2018). In our study, the most striking changes were recorded in the membranes of OMVs from the UV-exposed K. intermedius, compared to the OMVs from K. intermedius/iKMC, and this correlated with increased synthesis of lipids, especially, PLs, free FAs, and sterols, which could cause alteration in membrane fluidity.…”

Outer Membrane Lipid Secretion and the Innate Immune Response to Gram-Negative Bacteria

“…Bacteria form vesicles in broth culture, on solid media, in biofilms, and during intracellular and extracellular survival as part of pathogenic and mutualistic relationships with eukaryotes (166)(167)(168). Certain conditions favor blebbing, such as elevated temperature, interactions with quorum-sensing quinolones, antibiotic exposure, encounters with bacteriophage endolysins, and nutrient deprivation (169)(170)(171)(172)(173)(174). Their existence was described half of a century ago, yet we still do not firmly grasp how Gram-negative bacteria control OMV formation and regulate the secretion of lipids into their environment.…”