Long-Distance Delivery of Bacterial Virulence Factors by Pseudomonas aeruginosa Outer Membrane Vesicles

Abstract

Bacteria use a variety of secreted virulence factors to manipulate host cells, thereby causing significant morbidity and mortality. We report a mechanism for the long-distance delivery of multiple bacterial virulence factors, simultaneously and directly into the host cell cytoplasm, thus obviating the need for direct interaction of the pathogen with the host cell to cause cytotoxicity. We show that outer membrane–derived vesicles (OMV) secreted by the opportunistic human pathogen Pseudomonas aeruginosa deliver multiple virulence factors, including β-lactamase, alkaline phosphatase, hemolytic phospholipase C, and Cif, directly into the host cytoplasm via fusion of OMV with lipid rafts in the host plasma membrane. These virulence factors enter the cytoplasm of the host cell via N-WASP–mediated actin trafficking, where they rapidly distribute to specific subcellular locations to affect host cell biology. We propose that secreted virulence factors are not released individually as naked proteins into the surrounding milieu where they may randomly contact the surface of the host cell, but instead bacterial derived OMV deliver multiple virulence factors simultaneously and directly into the host cell cytoplasm in a coordinated manner.

Identification of a Novel Francisella tularensis Factor Required for Intramacrophage Survival and Subversion of Innate Immune Response

“…The support for our hypothesis comes from a recent report demonstrating that Francisella produces outer membrane vesicles that may serve as a "vesicle-mediated secretion" system to deliver bacterial proteins in the extracellular milieu (68). Outer membrane vesicles are spherical fragments of bacterial outer membrane that are produced continuously without the concomitant bacterial lysis by several Gram-negative bacteria to mediate inflammatory response and virulence in vivo (49,69). Interestingly, proteome characterization of outer membrane vesicles from F. novicida revealed the presence of FTN_0346, an ortholog of FTT0831c/FTL_0325 proteins of F. tularensis LVS and SchuS4, respectively (68).…”

Aggregatibacter actinomycetemcomitans Outer Membrane Vesicles Are Internalized in Human Host Cells and Trigger NOD1- and NOD2-Dependent NF-κB Activation

“…Control treatment corresponded to PBS which had been preincubated with PKH26 in the same manner as the OMVs. Where applicable, vesicles were incubated with cells in the presence of the inhibiting agent filipin III (Sigma-Aldrich) at a final concentration of 10 g/ml as in earlier studies (7,8,50). The inhibitor monensin (Sigma-Aldrich) was used at a final concentration of 2 M or 10 M. To estimate the effect of these inhibitors on cell viability, a neutral red uptake assay was carried out as described previously (51).…”

Role of extracellular membrane vesicles in the pathogenesis of various diseases, including cancer, renal diseases, atherosclerosis, and arthritis

“…51 Recently, it was shown that MVs of P. aeruginosa upon contact with the host plasma membrane lipid rafts, release virulence factors such as b-lactamase, ALP, hemolytic phospholipase C, and cystic fibrosis transmembrane factors (CiF) into the cytoplasm of the host cell. 101 Furuta et al 102 consider MVs of Porphyromonas gingivalis as 'targeted transport vehicles' that facilitate entry of virulence factors such as gingipains, which degrade host membrane proteins such as transferrin receptor, paxillin, and focal adhesion kinase, ultimately leading to cellular disruption. The shedding and release of such microvesicles in dental plaque accelerates inflammation in the surrounding host tissue through the release of proinflammatory mediators, thus leading to periodontitis.…”