Biocompatible bacteria-derived vesicles show inherent antimicrobial activity

Abstract

Up to 25,000 people die each year from resistant infections in Europe alone, with increasing incidence. It is estimated that a continued rise in bacterial resistance by 2050 would lead up to 10 million annual deaths worldwide, exceeding the incidence of cancer deaths. Although the design of new antibiotics is still one way to tackle the problem, pharmaceutical companies investigate far less into new drugs than 30 years ago. Incorporation of antibiotics into nanoparticle drug carriers ("nanoantibiotics") is currently investigated as a promising strategy to make existing antibiotics regain antimicrobial strength and overcome certain types of microbial drug resistance. Many of these synthetic systems enhance the antimicrobial effect of drugs by protecting antibiotics from degradation and reducing their side effects. Nevertheless, they often cannot selectively target pathogenic bacteria and -due to their synthetic origin -may induce side-effects themselves.In this work, we present the characterisation of naturally derived outer membrane vesicles (OMVs) as biocompatible and inherently antibiotic drug carriers. We isolated OMVs from two representative strains of myxobacteria, Cystobacter velatus Cbv34 and Sorangiineae species strain SBSr073, a bacterial order with the ability of lysing other bacterial strains and currently investigated as sources of new secondary metabolites. We investigated the myxobacterias' inherent antibacterial properties after isolation by differential centrifugation and purification by size-exclusion chromatography. OMVs have an average size range of 145-194 nm. We characterised their morphology by electron cryomicroscopy and found that OMVs are biocompatible with epithelial cells and differentiated macrophages. They showed a low endotoxin activity comparable to those of control samples, indicating a low acute inflammatory potential. In addition, OMVs showed inherent stability under different storage conditions, including 4 °C, -20 °C, -80 °C and freeze-drying. OMV uptake in Gram-negative model bacterium Escherichia coli (E. coli) showed similar to better incorporation than liposome controls, indicating the OMVs may interact with model bacteria via membrane fusion.Bacterial uptake correlated with antimicrobial activity of OMVs as measured by growth inhibition of E. coli. OMVs from Cbv34 inhibited growth of E. coli to a comparable extent as the clinically established antibiotic gentamicin. Liquid-chromatography coupled mass spectrometry analyses revealed the presence of cystobactamids in OMVs, inhibitors of bacterial topoisomerase currently studied to treat different Gram-negative and Gram-positive pathogens. This work, may serve as an important basis for further evaluation of OMVs derived from myxobacteria as novel therapeutic delivery systems against bacterial infections.

Natural and engineered bacterial outer membrane vesicles

“…However, limited by the unclear mechanism and the general bactericidal ability, this interesting phenomenon has not been studied thoroughly. Perhaps through the genetic engineering, OMVs can obtain amplified and controlled bactericidal ability, and the relative mechanism will be understood eventually in the future (Li et al 1998;Schulz et al 2018).…”

Mastering the Tools: Natural versus Artificial Vesicles in Nanomedicine

“…In particular, myxobacteria-derived OMVs retain an intrinsic antimicrobial activity, associated with the presence of cystobactamids, which are naturally occurring inside bacterial vesicles. [88] Additionally, bioengineered OMVs have been exploited as siRNAs delivery vehicles able to specifically kill cancer cells. [89] Plant-derived EVs (PEVs) are a time-and cost-efficient alternative to animal-derived EVs, with the additional benefit of increasing the total amount of vesicles that can be isolated per cell.…”

Myxobacteria-Derived Outer Membrane Vesicles: Potential Applicability Against Intracellular Infections

“…The remaining volume was used as an inoculum for the next passage of the myxobacterial culture. Growth curves of the cultures were established as described in a previous study [33].…”

“…Cryogenic transmission electron microscopy (cryo-TEM) was performed on OMVs pellets after ultracentrifugation and purified fractions as previously described [33]. Three to four microliters of the sample were dropped onto a holey carbon grid (type S147-4, Plano, Wetzlar, Germany) and plotted for 2 s before plunging into liquid ethane at T= −165 • C using a Gatan (Pleasanton, CA, USA) CP3 cryo plunger.…”

“…OMVs derived from myxobacteria have been shown to be involved in intercolony communication but also as predatory weapons against other bacteria [32]. We recently reported on myxobacterial OMVs with inherent antimicrobial properties due to their cystobactamid cargo [33]. Cystobactmids are topoisomerase inhibitors that have potent antibacterial activity [34].…”