Gram-negative and Gram-positive bacterial extracellular vesicles

Kill the Real with the Fake: Eliminate Intracellular Staphylococcus aureus Using Nanoparticle Coated with Its Extracellular Vesicle Membrane as Active-Targeting Drug Carrier

Staphylococcus aureus bacteremia is one of the most serious bacterial infections worldwide. Most complications of S. aureus bacteremia arise because the pathogen can survive inside host phagocytes, especially macrophages, which makes elimination of intracellular S. aureus key to clinical success. Unfortunately, most antibiotics have poor cellular penetration capacity, which necessitates intracellular delivery of antibiotics. We herein use nanoparticle coated with membrane of extracellular vesicle secreted by S. aureus (i.e., NP@EV) as active-targeting antibiotic carrier, with counterparts coated with PEGylated lipid bilayer (i.e., NP@Lipo; PEG = poly(ethylene glycol)) or with membrane of outer membrane vesicle secreted by Escherichia coli (i.e., NP@OMV) included as controls. NP@EV is internalized at higher efficiency by S. aureus-infected macrophage than by naïve counterpart, whereas NP@Lipo and NP@OMV are not; instead, NP@OMV, but neither NP@EV nor NP@Lipo, is internalized at higher efficiency by E. coli-infected macrophage than by naïve counterpart. Moreover, when injected intravenously into mouse models, NP@EV, but neither NP@OMV nor NP@Lipo, exhibits significantly higher accumulations within four major organs (kidney, lung, spleen, and heart) bearing metastatic S. aureus infections than within healthy counterparts. These observations suggest that EV membrane coating of NP@EV endows the particle with active targeting capacity both in vitro and in vivo. As a result, when preloaded with antibiotics and intravenously administered to alleviate metastatic infection in S. aureus bacteremia-bearing mouse model, NP@EV confers its cargoes with strikingly improved efficacy; in doing so, NP@EV is significantly more efficient than both NP@Lipo and NP@OMV in kidney and lung-which bear the highest metastatic bacterial burden and represent most common sites for S. aureus infection, respectively. Such an active-targeting delivery platform may have implications in promoting clinical success on intracellular pathogen-associated complications.

Extracellular Vesicle-Mimetic Ghost Nanovesicles for Delivering Anti-Inflammatory Drugs to Mitigate Gram-Negative Bacterial Outer Membrane Vesicle-Induced Systemic Inflammatory Response Syndrome

Sepsis is one of the major causes of death in hospital patients and is represented by systemic inflammatory response syndrome (SIRS) associated with infection. Gram-negative bacteria including Escherichia coli can provoke sepsis by stimulating the immune systems. Outer membrane vesicles (OMVs), nanosized vesicular structures derived from Gram-negative bacteria, contain several pathogen-associated molecular patterns, and are demonstrated to mediate SIRS. Here, extracellular vesicle-mimetic ghost nanovesicles loaded with dexamethasone, an anti-inflammatory drug, are developed using alkaline solution, sonication, and buoyant density gradient ultracentrifugation. These ghost nanovesicles have comparable physical features with naturally released extracellular vesicles but have 200-fold higher production yields than extracellular vesicles. Importantly, these ghost nanovesicles are devoid of potentially unwanted luminal cargos, including cytosolic proteins and nucleic acids. By maintaining the same topology as the parental cells, these dexamethasone-loaded ghost nanovesicles derived from human U937 monocytes reduce the release of interleukin-8 from OMV-treated endothelial cells in vitro, and mitigate the symptoms of OMV-induced SIRS in vivo. This study sheds light on using extracellular vesicle-mimetic ghost nanovesicles to deliver therapeutics to treat diseases such as bacterial sepsis.

Delivery of genome editing tools by bacterial extracellular vesicles

Here we propose to use bacterial cells as factories that generate EVs harboring both the RNP complex (or any other CRISPR-mediated tool) and a specific ligand molecule. The ligand would allow specific binding of EVs to cells with the matching receptors, adding a level of specificity to the delivery, hence stimulating precise genome editing.

Mycoplasmas are no exception to extracellular vesicles release: Revisiting old concepts

Release of extracellular vesicles (EV) by Gram-negative and positive bacteria is being frequently reported. EV are nano-sized, membrane-derived, non-self-replicating, spherical structures shed into the extracellular environment that could play a role in bacteria-host interactions. Evidence of EV production in bacteria belonging to the class Mollicutes, which are wall-less, is mainly restricted to the genus Acholeplasma and is scanty for the Mycoplasma genus that comprises major human and animal pathogens. Here EV release by six Mycoplasma (sub)species of clinical importance was investigated. EV were obtained under nutritional stress conditions, purified by ultracentrifugation and observed by electron microscopy. The membrane proteins of EV from three different species were further identified by mass spectrometry as a preliminary approach to determining their potential role in host-pathogen interactions. EV were shown to be released by all six (sub)species although their quantities and sizes (30-220 nm) were very variable. EV purification was complicated by the minute size of viable mycoplasmal cells. The proteins of EV-membranes from three (sub)species included major components of host-pathogen interactions, suggesting that EV could contribute to make the host-pathogen interplay more complex. The process behind EV release has yet to be deciphered, although several observations demonstrated their active release from the plasma membrane of living cells. This work shed new light on old concepts of "elementary bodies" and "not-cell bound antigens".

Comparative exoproteome profiling of an invasive and a commensal Staphylococcus haemolyticus isolate

Staphylococcus haemolyticus is a skin commensal emerging as an opportunistic pathogen. Nosocomial isolates of S. haemolyticus are the most antibiotic resistant members of the coagulase negative staphylococci (CoNS), but information about other S. haemolyticus virulence factors is scarce. Bacterial membrane vesicles (MVs) are one mediator of virulence by enabling secretion and long distance delivery of bacterial effector molecules while protecting the cargo from proteolytic degradation from the environment. We wanted to determine if the MV protein cargo of S. haemolyticus is strain specific and enriched in certain MV associated proteins compared to the totalsecretome. The present study shows that both clinical and commensal S. haemolyticus isolates produce membrane vesicles. The MV cargo of both strains was enriched in proteins involved in adhesion and acquisition of iron. The MV cargo of the clinical strain was further enriched in antimicrobial resistance proteins. Data are available via ProteomeXchange with identifier PXD010389. BIOLOGICAL SIGNIFICANCE: Clinical isolates of Staphylococcus haemolyticus are usually multidrug resistant, their main virulence factor is formation of biofilms, both factors leading to infections that are difficult to treat. We show that both clinical and commensal S. haemolyticus isolates produce membrane vesicles. Identification of staphylococcal membrane vesicles can potentially be used in novel approaches to combat staphylococcal infections, such as development of vaccines.

Calcite formation induced by Ensifer adhaerens, Microbacterium testaceum, Paeniglutamicibacter kerguelensis, Pseudomonas protegens and Rheinheimera texasensis

A wide range of bacterial species are able to induce calcium carbonate precipitation. Using our own laboratory-preserved strains, we have newly discovered that Ensifer sp. MY11e, Microbacterium sp. TMd9a1, Paeniglutamicibacter sp. MSa1a, Pseudomonas sp. GTc3, and Rheinheimera sp. ATWe6 can induce the formation of calcite crystals on an agar medium. Type strains of their closely related species (Ensifer adhaerens, Microbacterium testaceum, Paeniglutamicibacter kerguelensis, Pseudomonas protegens, and Rheinheimera texasensis) could also induce calcite formation. Although the initial pH value of the agar medium was 6.1, the pH of the agar media containing calcite, induced by cultivation of the 10 bacterial strains, increased to 8.0-8.4. The ammonification (oxidative deamination) of amino acids may been responsible for this increase in pH. The crystals formed both on and around the bacterial colonies. Furthermore, when these strains (excepting two Microbacterium strains) were cultivated on a cellulose acetate membrane filter (0.20 μm pore size) resting on the surface of the agar medium (i.e., in the membrane filter culture method), the crystals formed on the agar medium separate from the bacterial cells. These results indicate that the bacterial cells did not necessarily become nucleation sites for these crystals. We also investigated whether the studied strains could be applied to the biocementation of sand, and found that only two Ensifer strains were able to form large sand lumps.

Extracellular Vesicles in Joint Disease and Therapy

The use of extracellular vesicles (EVs) as a potential therapy is currently explored for different disease areas. When it comes to the treatment of joint diseases this approach is still in its infancy. As in joint diseases both inflammation and the associated articular tissue destruction are important factors, both the immune-suppressive and the regenerative properties of EVs are potentially advantageous characteristics for future therapy. There is, however, only limited knowledge on the basic features, such as numerical profile and function, of EVs in joint articular tissues in general and their linking medium, the synovial fluid, in particular. Further insight is urgently needed in order to appreciate the full potential of EVs and to exploit these in EV-mediated therapies. Physiologic joint homeostasis is a prerequisite for proper functioning of joints and we postulate that EVs play a key role in the regulation of joint homeostasis and hence can have an important function in re-establishing disturbed joint homeostasis, and, in parallel, in the regeneration of articular tissues. In this mini-review EVs in the joint are explained from a historical perspective in both health and disease, including the potential niche for EVs in articular tissue regeneration. Furthermore, the translational potential of equine models for human joint biology is discussed. Finally, the use of MSC-derived EVs that is recently gaining ground is highlighted and recommendations are given for further EV research in this field.

Helicobacter pylori outer membrane vesicles involvement in the infection development and Helicobacter pylori-related diseases

Helicobacter pylori - (H. pylori) play a role in the pathogenesis of gastritis, gastric and duodenal ulcers as well as gastric cancer. A possible involvement of outer membrane vesicles (OMVs) produced by H. pylori in the distribution of bacterial antigens through the gastric epithelial barrier and their role in the development of local and systemic host inflammatory and immune responses has been suggested. OMVs contain various biologically active compounds, which internalize into host cells affecting signaling pathways and promoting apoptosis of gastric epithelial and immunocompetent cells. OMVs-associated H. pylori virulence factors may strengthen or downregulate the immune responses leading to disease development. This review describes the biological importance of H. pylori OMVs and their role in the course of H. pylori infections, as well as H. pylori related local and systemic effects.

The implementation of omics technologies in cancer microbiome research

Whilst the interplay between host genetics and the environment plays a pivotal role in the aetiopathogenesis of cancer, there are other key contributors of importance as well. One such factor of central and growing interest is the contribution of the microbiota to cancer. Even though the field is only a few years old, investigation of the 'cancer microbiome' has already led to major advances in knowledge of the basic biology of cancer risk and progression, opened novel avenues for biomarkers and diagnostics, and given a better understanding of mechanisms underlying response to therapy. Recent developments in microbial DNA sequencing techniques (and the bioinformatics required for analysis of these datasets) have allowed much more in-depth profiling of the structure of microbial communities than was previously possible. However, for more complete assessment of the functional implications of microbial changes, there is a growing recognition of the importance of the integration of microbial profiling with other omics modalities, with metabonomics (metabolite profiling) and proteomics (protein profiling) both gaining particular recent attention. In this review, we give an overview of some of the key scientific techniques being used to unravel the role of the cancer microbiome. We have aimed to highlight practical aspects related to sample collection and preparation, choice of the modality of analysis, and examples of where different omics technologies have been complementary to each other to highlight the significance of the cancer microbiome.

Lactobacillus plantarum-derived Extracellular Vesicles Protect Atopic Dermatitis Induced by Staphylococcus aureus-derived Extracellular Vesicles

PURPOSE

The microbial environment is an important factor that contributes to the pathogenesis of atopic dermatitis (AD). Recently, it was revealed that not only bacteria itself but also extracellular vesicles (EVs) secreted from bacteria affect the allergic inflammation process. However, almost all research carried out so far was related to local microorganisms, not the systemic microbial distribution. We aimed to compare the bacterial EV composition between AD patients and healthy subjects and to experimentally find out the beneficial effect of some bacterial EV composition.

METHODS

Twenty-seven AD patients and 6 healthy control subjects were enrolled. After urine and serum were obtained, EVs were prepared from samples. Metagenomic analysis of 16s ribosomal DNA extracted from the EVs was performed, and bacteria showing the greatest difference between controls and patients were identified. In vitro and in vivo therapeutic effects of significant bacterial EV were evaluated with keratinocytes and with Staphylococcus aureus-induced mouse AD models, respectively.

RESULTS

The proportions of Lactococcus, Leuconostoc and Lactobacillus EVs were significantly higher and those of Alicyclobacillus and Propionibacterium were lower in the control group than in the AD patient group. Therefore, lactic acid bacteria were considered to be important ones that contribute to the difference between the patient and control groups. In vitro, interleukin (IL)-6 from keratinocytes and macrophages decreased and cell viability was restored with Lactobacillus plantarum-derived EV treatment prior to S. aureus EV treatment. In S. aureus-induced mouse AD models, L. plantarum-derived EV administration reduced epidermal thickening and the IL-4 level.

CONCLUSIONS

We suggested the protective role of lactic acid bacteria in AD based on metagenomic analysis. Experimental findings further suggest that L. plantarum-derived EV could help prevent skin inflammation.

Staphylococcus aureus Extracellular Vesicles Elicit an Immunostimulatory Response in vivo on the Murine Mammary Gland

Staphylococcus aureus is a major pathogen responsible for bovine mastitis, the most common and costly disease affecting dairy cattle. S. aureus naturally releases extracellular vesicles (EVs) during its growth. EVs play an important role in the bacteria-bacteria and bacteria-host interactions and are notably considered as nanocarriers that deliver virulence factors to the host tissues. Whether EVs play a role in a mastitis context is still unknown. In this work, we showed that S. aureus Newbould 305 (N305), a bovine mastitis isolate, has the ability to generate EVs in vitro with a designated protein content. Purified S. aureus N305-secreted EVs were not cytotoxic when tested in vitro on MAC-T and PS, two bovine mammary epithelial cell lines. However, they induced the gene expression of inflammatory cytokines at levels similar to those induced by live S. aureus N305. The in vivo immune response to purified S. aureus N305-secreted EVs was tested in a mouse model for bovine mastitis and their immunogenic effect was compared to that of live S. aureus N305, heat-killed S. aureus N305 and to S. aureus lipoteichoic acid (LTA). Clinical and histopathological signs were evaluated and pro-inflammatory and chemotactic cytokine levels were measured in the mammary gland 24 h post-inoculation. Live S. aureus induced a significantly stronger inflammatory response than that of any other condition tested. Nevertheless, S. aureus N305-secreted EVs induced a dose-dependent neutrophil recruitment and the production of a selected set of pro-inflammatory mediators as well as chemokines. This immune response elicited by intramammary S. aureus N305-secreted EVs was comparable to that of heat-killed S. aureus N305 and, partly, by LTA. These results demonstrated that S. aureus N305-secreted EVs induce a mild inflammatory response distinct from the live pathogen after intramammary injection. Overall, our combined in vitro and in vivo data suggest that EVs are worth to be investigated to better understand the S. aureus pathogenesis and are relevant tools to develop strategies against bovine S. aureus mastitis.

Gram-Positive Bacterial Extracellular Vesicles and Their Impact on Health and Disease

During recent years it has become increasingly clear that the release of extracellular vesicles (EVs) is a feature inherent to all cellular life forms. These lipid bilayer-enclosed particles are secreted by members of all domains of life: Eukarya, Bacteria and Archaea, being similar in size, general composition, and potency as a functional entity. Noticeably, the recent discovery of EVs derived from bacteria belonging to the Gram-positive phyla Actinobacteria and Firmicutes has added a new layer of complexity to our understanding of bacterial physiology, host interactions, and pathogenesis. Being nano-sized structures, Gram-positive EVs carry a large diversity of cargo compounds, including nucleic acids, viral particles, enzymes, and effector proteins. The diversity in cargo molecules may point to roles of EVs in bacterial competition, survival, material exchange, host immune evasion and modulation, as well as infection and invasion. Consequently, the impact of Gram-positive EVs on health and disease are being revealed gradually. These findings have opened up new leads for the development of medical advances, including strategies for vaccination and anti-bacterial treatment. The rapidly advancing research into Gram-positive EVs is currently in a crucial phase, therefore this review aims to give an overview of the groundwork that has been laid at present and to discuss implications and future challenges of this new research field.

Drug Repositioning to Alleviate Systemic Inflammatory Response Syndrome Caused by Gram-Negative Bacterial Outer Membrane Vesicles

Sepsis is characterized by systemic inflammatory response syndrome (SIRS) accompanied with infection. Gram-negative bacteria can evoke sepsis by activating the host immune system, such as the release of IL-6 and TNF-α, through their virulence factors. Outer membrane vesicles (OMVs), nanosized bilayered proteolipids derived from Gram-negative bacteria, harbor various virulence factors and are shown to induce SIRS. Here, drugs are repositioned to alleviate SIRS caused by Gram-negative bacterial OMVs. Using novel OMV-based drug screening systems, a total of 178 commercially available drugs are primarily screened, and a total of 18 repositioned drug candidates are found to effectively block IL-6 and TNF-α production from OMV-stimulated macrophages. After excluding the compounds which are previously known to intervene sepsis or which show cytotoxicity to macrophages, the compounds which show dose-dependency in inhibiting the release of IL-6 and TNF-α by the OMV-stimulated macrophages in vitro and which reduce OMV-induced SIRS in vivo are selected. Salbutamol, a β2 adrenergic receptor agonist, is selected as a novel candidate to alleviate OMV-induced SIRS. This study sheds light on using Gram-negative bacterial OMVs in exploring novel candidate compounds to alleviate inflammatory diseases including sepsis.

Extracellular Vesicles as Markers and Mediators in Sepsis

Sepsis is defined as life-threatening organ dysfunction caused by a dysregulated host response to infection. It remains a highly lethal condition in which current tools for early diagnosis and therapeutic decision-making are far from ideal. Extracellular vesicles (EVs), 30 nm to several micrometers in size, are released from cells upon activation and apoptosis and express membrane epitopes specific for their parental cells. Since their discovery two decades ago, their role as biomarkers and mediators in various diseases has been intensively studied. However, their potential importance in the sepsis syndrome has gained attention only recently. Sepsis and EVs are both complex fields in which standardization has long been overdue. In this review, several topics are discussed. First, we review current studies on EVs in septic patients with emphasis on their variable quality and clinical utility. Second, we discuss the diagnostic and therapeutic potential of EVs as well as their role as facilitators of cell communication via micro RNA and the relevance of micro-organism-derived EVs. Third, we give an overview over the potential beneficial but also detrimental roles of EVs in sepsis. Finally, we focus on the role of EVs in selected intensive care scenarios such as coagulopathy, mechanical ventilation and blood transfusion. Overall, the prospect for EV use in septic patients is bright, ranging from rapid and precise (point-of-care) diagnostics, prevention of harmful iatrogenic interventions, to using EVs as guides of individualized therapy. Before the above is achieved, however, the EV research field requires reliable standardization of the current methods and development of new analytical procedures that can close the existing technological gaps.

A novel extracellular vesicle-associated endodeoxyribonuclease helps Streptococcus pneumoniae evade neutrophil extracellular traps and is required for full virulence

Streptococcus pneumoniae (pneumococcus) is a major bacterial pathogen that causes pneumonia and septicemia in humans. Pneumococci are cleared from the host primarily by antibody dependent opsonophagocytosis by phagocytes like neutrophils. Neutrophils release neutrophil extracellular traps (NETs) on contacting pneumococci. NETs immobilize pneumococci and restrict its dissemination in the host. One of the strategies utilized by pneumococci to evade the host immune response involves use of DNase(s) to degrade NETs. We screened the secretome of autolysin deficient S. pneumoniae to identify novel DNase(s). Zymogram analysis revealed 3 bands indicative of DNase activity. Mass spectrometric analysis led to the identification of TatD as a potential extracellular DNase. Recombinant TatD showed nucleotide sequence-independent endodeoxyribonuclease activity. TatD was associated with extracellular vesicles. Pneumococcal secretome degraded NETs from human neutrophils. Extracellular vesicle fraction from tatD deficient strain showed little NET degrading activity. Recombinant TatD efficiently degraded NETs. tatD deficient pneumococci showed lower bacterial load in lungs, blood and spleen in a murine sepsis model compared to wildtype strain, and showed less severe lung pathology and compromised virulence. This study provides insights into the role of a novel extracellular DNase in evasion of the innate immune system.

Comparative lipidomic profiling of the human commensal bacterium Propionibacterium acnes and its extracellular vesicles

Propionibacterium acnes is a lipophilic commensal bacterium mainly found on the skin and in the gastrointestinal tract. Pathophysiological effects of P. acnes have recently been reported not only in acne progression but in various diseases. As an emerging mode of bacterial communication, extracellular vesicles (EVs) have been demonstrated to conduct critical pathophysiological functions. To provide information on P. acnes lipid composition for the first time, we conducted a comparative lipidomic analysis of P. acnes and P. acnes EVs and identified 214 lipids with high confidence using triplicated liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analyses. P. acnes EVs contained substantially more PCs, DGs, PAs, PEs, LPAs, LPCs, and MGs than P. acnes, and contained fewer PSs, SO1Ps, SA1Ps, LPGs, LPIs, and LPSs. Distinctively, P. acnes EVs possessed a markedly reduced amount of TG. These findings will provide useful clues for understanding the biological and pathophysiological mechanisms of P. acnes and for clinical applications such as vaccine development, diagnostics and therapeutics.

Release of Staphylococcus aureus extracellular vesicles and their application as a vaccine platform

Secretion of extracellular vesicles (EVs), a process common to eukaryotes, archae, and bacteria, represents a secretory pathway that allows cell-free intercellular communication. Microbial EVs package diverse proteins and influence the host-pathogen interaction, but the mechanisms underlying EV production in Gram-positive bacteria are poorly understood. Here we show that EVs purified from community-associated methicillin-resistant Staphylococcus aureus package cytosolic, surface, and secreted proteins, including cytolysins. Staphylococcal alpha-type phenol-soluble modulins promote EV biogenesis by disrupting the cytoplasmic membrane; whereas, peptidoglycan cross-linking and autolysin activity modulate EV production by altering the permeability of the cell wall. We demonstrate that EVs purified from a S. aureus mutant that is genetically engineered to express detoxified cytolysins are immunogenic in mice, elicit cytolysin-neutralizing antibodies, and protect the animals in a lethal sepsis model. Our study reveals mechanisms underlying S. aureus EV production and highlights the usefulness of EVs as a S. aureus vaccine platform.

Extracellular vesicles (EVs) influence host-pathogen interactions, but EV biogenesis in gram-positive bacteria remains elusive. Here authors characterize EVs from Staphylococcus aureus and show that phenol-soluble modulins and autolysins promote EV biogenesis by disrupting the membrane and cell wall.

Immunomodulatory Effects of Pneumococcal Extracellular Vesicles on Cellular and Humoral Host Defenses

Gram-positive bacteria, including the major respiratory pathogen Streptococcus pneumoniae, were recently shown to produce extracellular vesicles (EVs) that likely originate from the plasma membrane and are released into the extracellular environment. EVs may function as cargo for many bacterial proteins, however, their involvement in cellular processes and their interactions with the innate immune system are poorly understood. Here, EVs from pneumococci were characterized and their immunomodulatory effects investigated. Pneumococcal EVs were protruding from the bacterial surface and released into the medium as 25 to 250 nm lipid stained vesicles containing a large number of cytosolic, membrane, and surface-associated proteins. The cytosolic pore-forming toxin pneumolysin was significantly enriched in EVs compared to a total bacterial lysate but was not required for EV formation. Pneumococcal EVs were internalized into A549 lung epithelial cells and human monocyte-derived dendritic cells and induced proinflammatory cytokine responses irrespective of pneumolysin content. EVs from encapsulated pneumococci were recognized by serum proteins, resulting in C3b deposition and formation of C5b-9 membrane attack complexes as well as factor H recruitment, depending on the presence of the choline binding protein PspC. Addition of EVs to human serum decreased opsonophagocytic killing of encapsulated pneumococci. Our data suggest that EVs may act in an immunomodulatory manner by allowing delivery of vesicle-associated proteins and other macromolecules into host cells. In addition, EVs expose targets for complement factors in serum, promoting pneumococcal evasion of humoral host defense.

Streptococcus pneumoniae is a major contributor to morbidity and mortality worldwide, being the major cause of milder respiratory tract infections such as otitis and sinusitis and of severe infections such as community-acquired pneumonia, with or without septicemia, and meningitis. More knowledge is needed on how pneumococci interact with the host, deliver virulence factors, and activate immune defenses. Here we show that pneumococci form extracellular vesicles that emanate from the plasma membrane and contain virulence properties, including enrichment of pneumolysin. We found that pneumococcal vesicles can be internalized into epithelial and dendritic cells and bind complement proteins, thereby promoting pneumococcal evasion of complement-mediated opsonophagocytosis. They also induce pneumolysin-independent proinflammatory responses. We suggest that these vesicles can function as a mechanism for delivery of pneumococcal proteins and other immunomodulatory components into host cells and help pneumococci to avoid complement deposition and phagocytosis-mediated killing, thereby possibly contributing to the symptoms found in pneumococcal infections.

Versatile effects of bacterium-released membrane vesicles on mammalian cells and infectious/inflammatory diseases

Gram-negative bacterium-released outer-membrane vesicles (OMVs) and Gram-positive bacterium-released membrane vesicles (MVs) share significant similarities with mammalian cell-derived MVs (eg, microvesicles and exosomes) in terms of structure and their biological activities. Recent studies have revealed that bacterial OMVs/MVs could (1) interact with immune cells to regulate inflammatory responses, (2) transport virulence factors (eg, enzymes, DNA and small RNAs) to host cells and result in cell injury, (3) enhance barrier function by stimulating the expression of tight junction proteins in intestinal epithelial cells, (4) upregulate the expression of endothelial cell adhesion molecules, and (5) serve as natural nanocarriers for immunogenic antigens, enzyme support and drug delivery. In addition, OMVs/MVs can enter the systemic circulation and induce a variety of immunological and metabolic responses. This review highlights the recent advances in the understanding of OMV/MV biogenesis and their compositional remodeling. In addition, interactions between OMVs/MVs and various types of mammalian cells (ie, immune cells, epithelial cells, and endothelial cells) and their pathological/preventive effects on infectious/inflammatory diseases are summarized. Finally, methods for engineering OMVs/MVs and their therapeutic potential are discussed.

Safe Staphylococcal Platform for the Development of Multivalent Nanoscale Vesicles against Viral Infections

Many viruses often have closely related yet antigenically distinct serotypes. An ideal vaccine against viral infections should induce a multivalent and protective immune response against all serotypes. Inspired by bacterial membrane vesicles (MVs) that carry different protein components, we constructed an agr locus deletion mutant of the Staphylococcus aureus strain (RN4220-Δagr) to reduce potential toxicity. Nanoscale vesicles derived from this strain (^ΔagrMVs) carry at least four major components that can deliver heterologous antigens. These components were each fused with a triple FLAG tag, and the tagged proteins could be incorporated into the ^ΔagrMVs. The presentation levels were (3.43 ± 0.73)%, (5.07 ± 0.82)%, (2.64 ± 0.61)%, and (2.89 ± 0.74)% of the total ^ΔagrMV proteins for Mntc-FLAG, PdhB-FLAG, PdhA-FLAG, and Eno-FLAG, respectively. With two DENV envelope E domain III proteins (EDIIIconA and EDIIIconB) as models, the DENV EDIIIconA and EDIIIconB delivered by two staphylococcal components were stably embedded in the ^ΔagrMVs. Administration of such engineered ^ΔagrMVs in mice induced antibodies against all four DENV serotypes. Sera from immunized mice protected Vero cells and suckling mice from a lethal challenge of DENV-2. This study will open up new insights into the preparation of multivalent nanosized viral vaccines against viral infections.

Molecular Paths Linking Metabolic Diseases, Gut Microbiota Dysbiosis and Enterobacteria Infections

Alterations of both ecology and functions of gut microbiota are conspicuous traits of several inflammatory pathologies, notably metabolic diseases such as obesity and type 2 diabetes. Moreover, the proliferation of enterobacteria, subdominant members of the intestinal microbial ecosystem, has been shown to be favored by Western diet, the strongest inducer of both metabolic diseases and gut microbiota dysbiosis. The inner interdependence between the host and the gut microbiota is based on a plethora of molecular mechanisms by which host and intestinal microbes modify each other. Among these mechanisms are as follows: (i) the well-known metabolic impact of short chain fatty acids, produced by microbial fermentation of complex carbohydrates from plants; (ii) a mutual modulation of miRNAs expression, both on the eukaryotic (host) and prokaryotic (gut microbes) side; (iii) the production by enterobacteria of virulence factors such as the genotoxin colibactin, shown to alter the integrity of host genome and induce a senescence-like phenotype in vitro; (iv) the microbial excretion of outer-membrane vesicles, which, in addition to other functions, may act as a carrier for multiple molecules such as toxins to be delivered to target cells. In this review, I describe the major molecular mechanisms by which gut microbes exert their metabolic impact at a multi-organ level (the gut barrier being in the front line) and support the emerging triad of metabolic diseases, gut microbiota dysbiosis and enterobacteria infections.

New Technologies for Analysis of Extracellular Vesicles

Extracellular vesicles (EVs) are diverse, nanoscale membrane vesicles actively released by cells. Similar-sized vesicles can be further classified (e.g., exosomes, microvesicles) based on their biogenesis, size, and biophysical properties. Although initially thought to be cellular debris, and thus under-appreciated, EVs are now increasingly recognized as important vehicles of intercellular communication and circulating biomarkers for disease diagnoses and prognosis. Despite their clinical potential, the lack of sensitive preparatory and analytical technologies for EVs poses a barrier to clinical translation. New analytical platforms including molecular ones are thus actively being developed to address these challenges. Recent advances in the field are expected to have far-reaching impact in both basic and translational studies. This article aims to present a comprehensive and critical overview of emerging analytical technologies for EV detection and their clinical applications.

Rapid naked-eye detection of Gram-positive bacteria by vancomycin-based nano-aggregation

Development of a rapid, point-of-care assay for diagnosing bacterial infections is crucial for subsequent treatment of the patient and preventing the overuse of antibiotics. Herein, we describe a rapid, one-step colorimetric assay based on the formation of nano-aggregates using nanobeads targeting Gram-positive bacteria. Vancomycin was immobilized onto blue-colored polymeric nanobeads to induce specific and multivalent binding with the Gram-positive bacterial cell wall and subsequent agglomeration. Without any pre-processing steps, the addition of various types of Gram-positive pathogens to the nanobeads resulted in the formation of blue precipitates, which could be observed with the naked eye in ∼30 min. We also utilized a porous filter system for the assay, which allowed discrimination of Gram-positive targets with higher selectivity, and demonstrated feasibility as a simple diagnostic assay with minimal technical components. We anticipate that the nanobead aggregation assay can be potentially applied as a rapid and simple sensing platform, which can be easily miniaturized and enable point-of-care diagnosis of Gram-positive infections.

A rapid, colorimetric assay based on aggregation of nanobeads functionalized with vancomycin is developed for naked-eye detection of Gram-positive bacteria.

Structure, function and regulation of Pseudomonas aeruginosa porins

Pseudomonas aeruginosa is a Gram-negative bacterium belonging to the γ-proteobacteria. Like other members of the Pseudomonas genus, it is known for its metabolic versatility and its ability to colonize a wide range of ecological niches, such as rhizosphere, water environments and animal hosts, including humans where it can cause severe infections. Another particularity of P. aeruginosa is its high intrinsic resistance to antiseptics and antibiotics, which is partly due to its low outer membrane permeability. In contrast to Enterobacteria, pseudomonads do not possess general diffusion porins in their outer membrane, but rather express specific channel proteins for the uptake of different nutrients. The major outer membrane 'porin', OprF, has been extensively investigated, and displays structural, adhesion and signaling functions while its role in the diffusion of nutrients is still under discussion. Other porins include OprB and OprB2 for the diffusion of glucose, the two small outer membrane proteins OprG and OprH, and the two porins involved in phosphate/pyrophosphate uptake, OprP and OprO. The remaining nineteen porins belong to the so-called OprD (Occ) family, which is further split into two subfamilies termed OccD (8 members) and OccK (11 members). In the past years, a large amount of information concerning the structure, function and regulation of these porins has been published, justifying why an updated review is timely.

Mannheimia haemolytica A2 secretes different proteases into the culture medium and in outer membrane vesicles

Respiratory diseases in ruminants have a significantly negative impact on the worldwide economy. The bacterium Mannheimia haemolytica is involved in pneumonic infections in bovine and ovine. In gram-negative bacteria, six secretion systems related to the colonization process and host tissue damage have been reported. In addition, in the last two decades, the production of outer membrane vesicles has been studied as a different bacterial strategy to release virulence factors, such as exotoxins, lipopolysaccharides, and proteases. However, in M. haemolytica serotype A2, protease secretion and release in vesicles have not been reported as virulence mechanisms. The aim of this work was to identify proteases released into the culture supernatant and in vesicles of M. haemolytica A2. Our results showed evident differences in the molecular mass and activity of proteases present in culture supernatants and outer membrane vesicles based on zymography assays. The biochemical characterization of M. haemolytica proteases revealed that the main types were cysteine and metalloproteases. A specific metalloprotease of 100 kDa was active in the culture supernatants, but it was not active and was found in low quantities in vesicles. Proteases could be an important virulence factor during the infectious pneumonic process led by M. haemolytica.

Tiny but mighty: bacterial membrane vesicles in food biotechnological applications

Membrane vesicle (MV) production is observed in all domains of life. Evidence of MV production accumulated in recent years among bacterial species involved in fermentation processes. These studies revealed MV composition, biological functions and properties, which made us recognize the potential of MVs in food applications as delivery vehicles of various compounds to other bacteria or the human host. Moreover, MV producing strains can deliver benefits as probiotics or starters in fermentation processes. Next to the natural production of MVs, we also highlight possible methods for artificial generation of bacterial MVs and cargo loading to enhance their applicability. We believe that a more in-depth understanding of bacterial MVs opens new avenues for their exploitation in biotechnological applications.

Bacterial outer membrane vesicles suppress tumor by interferon-γ-mediated antitumor response

Gram-negative bacteria actively secrete outer membrane vesicles, spherical nano-meter-sized proteolipids enriched with outer membrane proteins, to the surroundings. Outer membrane vesicles have gained wide interests as non-living complex vaccines or delivery vehicles. However, no study has used outer membrane vesicles in treating cancer thus far. Here we investigate the potential of bacterial outer membrane vesicles as therapeutic agents to treat cancer via immunotherapy. Our results show remarkable capability of bacterial outer membrane vesicles to effectively induce long-term antitumor immune responses that can fully eradicate established tumors without notable adverse effects. Moreover, systematically administered bacterial outer membrane vesicles specifically target and accumulate in the tumor tissue, and subsequently induce the production of antitumor cytokines CXCL10 and interferon-γ. This antitumor effect is interferon-γ dependent, as interferon-γ-deficient mice could not induce such outer membrane vesicle-mediated immune response. Together, our results herein demonstrate the potential of bacterial outer membrane vesicles as effective immunotherapeutic agent that can treat various cancers without apparent adverse effects.

Bacterial outer membrane vesicles (OMVs) contain immunogens but no study has yet examined their potential in treating cancer. Here, the authors demonstrate that OMVs can suppress established tumours and prevent tumour metastasis by an interferon-γ mediated antitumor response.

A Metagenomic Analysis Provides a Culture-Independent Pathogen Detection for Atopic Dermatitis

PURPOSE

Atopic dermatitis (AD) is an inflammatory skin disease, significantly affecting the quality of life. Using AD as a model system, we tested a successive identification of AD-associated microbes, followed by a culture-independent serum detection of the identified microbe.

METHODS

A total of 43 genomic DNA preparations from washing fluid of the cubital fossa of 6 healthy controls, skin lesions of 27 AD patients, 10 of which later received treatment (post-treatment), were subjected to high-throughput pyrosequencing on a Roche 454 GS-FLX platform.

RESULTS

Microbial diversity was decreased in AD, and was restored following treatment. AD was characterized by the domination of Staphylococcus, Pseudomonas, and Streptococcus, whereas Alcaligenaceae (f), Sediminibacterium, and Lactococcus were characteristic of healthy skin. An enzyme-linked immunosorbent assay (ELISA) showed that serum could be used as a source for the detection of Staphylococcus aureus extracellular vesicles (EVs). S. aureus EV-specific immunoglobulin G (IgG) and immunoglobulin E (IgE) were quantified in the serum.

CONCLUSIONS

A metagenomic analysis together with a serum detection of pathogen-specific EVs provides a model for successive identification and diagnosis of pathogens of AD.

Genetic cargo and bacterial species set the rate of vesicle-mediated horizontal gene transfer

Most bacteria release extracellular vesicles (EVs). Recent studies have found these vesicles are capable of gene delivery, however the consequences of vesicle-mediated transfer on the patterns and rates of gene flow within microbial communities remains unclear. Previous studies have not determined the impact of both the genetic cargo and the donor and recipient species on the rate of vesicle-mediated gene exchange. This report examines the potential for EVs as a mechanism of gene transfer within heterogeneous microbial populations. EVs were harvested from three species of Gram-negative microbes carrying different plasmids. The dynamics of gene transfer into recipient species was measured. This study demonstrates that vesicles enable gene exchange between five species of Gram-negative bacteria, and that the identity of the genetic cargo, donor strain, and recipient strain all influence gene transfer rates. Each species released and acquired vesicles containing genetic material to a variable degree, and the transfer rate did not correlate with the relatedness of the donor and recipient species. The results suggest that EVs may be a general mechanism to exchange non-specialized genetic cargo between bacterial species.

Overexpression of MicA induces production of OmpC-enriched outer membrane vesicles that protect against Salmonella challenge

Outer membrane vesicles (OMVs) derived from bacteria are promising candidates for subunit vaccines. Stresses that modulate the composition of outer membrane proteins (OMPs) are important for OMV synthesis. Small RNAs (sRNAs) expressed in response to stress regulate OMPs, although the mechanism underlying sRNA-mediated OMV biogenesis and its utility for developing vaccine platforms remains to be elucidated. Here, we characterized the role of a sRNA, MicA, which regulates OmpA, a major OMP involved in both production of OMVs and reactive immunity against Salmonella challenge. A Salmonella strain overexpressing MicA generated more OMVs than a control strain. In addition, OmpC was the major component of MicA-derived OMV proteins. MicA-derived OMVs induced Th1- and Th17-type immune responses in vitro and reduced Salmonella-mediated lethality in a mouse model. Thus, OmpA-regulatory sRNA-derived OMVs may facilitate production of Salmonella-protective vaccines.

Dendritic Cell Sensing of Hydrophobic Di- and Triacylated Lipopeptides Self-Assembled within Synthetic Virus-like Particles

Dendritic cells (DCs) play critical roles in developing immune defenses. One important aspect is interaction with pathogen-associated molecular patterns (PAMPs)/danger-associated molecular patterns, including di- and triacylated lipopeptides. Isolated or synthetic lipopeptides are potent vaccine adjuvants, interacting with cell surface TLR2 heterodimers. In contrast, deep embedment within bacteria cell walls would impair lipopeptide interaction with cell surface TLR2, requiring degradation for PAMP recognition. Accordingly, DC processing in the absence of surface TLR2 ligation was defined using synthetic virus-like particles (SVLPs) carrying hydrophobic TLR2 PAMPs within di- and triacylated lipopeptide cores (P2Cys-SVLPs and P3Cys-SVLPs) compared with SVLPs lacking immunomodulatory lipopeptides. DCs rapidly and efficiently internalized SVLPs, which was dominated by slow endocytic processing via macropinocytosis, although some caveolar endocytosis was implicated. This delivered SVLPs primarily into macropinosomes often interacting with EEA-1⁺ early endosomes. Although endoplasmic reticulum association was occasionally noted, association with recycling/sorting structures was not observed. Involvement of LysoTracker⁺ structures slowly increased with time, with SVLPs present in such structures ultimately dominating. Only SVLPs carrying di- and triacylated lipopeptide cores induced DC activation and maturation independently of surface TLR2 ligation. Intracellular recognition of SVLP TLR2 ligands was confirmed by observing SVLPs' association with internal TLR2, which had similar kinetics to SVLP association with LysoTracker. This related to inflammatory cytokine induction by SVLP⁺ DCs, with adaptive immune response activation ex vivo/in vivo. Importantly, particular DCs, not monocytes, recognized intracellular exposure of the TLR2 PAMPs carried by di- and triacylated SVLP cores, which indicates subset-distinct recognition of functional internal TLR2 ligands. Thus, vaccines carrying hydrophobic TLR2 ligands would interact with particular DCs for efficient induction of specific immunity in the absence of additional adjuvant.

The Therapeutic Benefit of Bacterial Membrane Vesicles

The therapeutic potential of extracellular vesicles from eukaryotes has gained strong interest in recent years. However, research into the therapeutic application of their bacterial counterparts, known as bacterial membrane vesicles, is only just beginning to be appreciated. Membrane vesicles (MVs) from both Gram-positive and Gram-negative bacteria offer significant advantages in therapeutic development, including large-scale, cost effective production and ease of molecular manipulation to display foreign antigens. The nanoparticle size of MVs enables their dissemination through numerous tissue types, and their natural immunogenicity and self-adjuvanting capability can be harnessed to induce both cell-mediated and humoral immunity in vaccine design. Moreover, the ability to target MVs to specific tissues through the display of surface receptors raises their potential use as targeted MV-based anti-cancer therapy. This review discusses recent advances in MV research with particular emphasis on exciting new possibilities for the application of MVs in therapeutic design.

Mechanisms for Pseudoalteromonas piscicida-Induced Killing of Vibrios and Other Bacterial Pathogens

Pseudoalteromonas piscicida is a Gram-negative gammaproteobacterium found in the marine environment. Three strains of pigmented P. piscicida were isolated from seawater and partially characterized by inhibition studies, electron microscopy, and analysis for proteolytic enzymes. Growth inhibition and death occurred around colonies of P. piscicida on lawns of the naturally occurring marine pathogens Vibrio vulnificus, Vibrio parahaemolyticus, Vibrio cholerae, Photobacterium damselae, and Shewanella algae Inhibition also occurred on lawns of Staphylococcus aureus but not on Escherichia coli O157:H7 or Salmonella enterica serovar Typhimurium. Inhibition was not pH associated, but it may have been related to the secretion of a cysteine protease with strong activity, as detected with a synthetic fluorogenic substrate. This diffusible enzyme was secreted from all three P. piscicida strains. Direct overlay of the Pseudoalteromonas colonies with synthetic fluorogenic substrates demonstrated the activity of two aminopeptidase Bs, a trypsin-like serine protease, and enzymes reactive against substrates for cathepsin G-like and caspase 1-like proteases. In seawater cultures, scanning electron microscopy revealed numerous vesicles tethered to the outer surface of P. piscicida and a novel mechanism of direct transfer of these vesicles to V. parahaemolyticus Vesicles digested holes in V. parahaemolyticus cells, while the P. piscicida congregated around the vibrios in a predatory fashion. This transfer of vesicles and vesicle-associated digestion of holes were not observed in other bacteria, suggesting that vesicle binding may be mediated by host-specific receptors. In conclusion, we show two mechanisms by which P. piscicida inhibits and/or kills competing bacteria, involving the secretion of antimicrobial substances and the direct transfer of digestive vesicles to competing bacteria.IMPORTANCEPseudoalteromonas species are widespread in nature and reduce competing microflora by the production of antimicrobial compounds. We isolated three strains of P. piscicida and characterized secreted and cell-associated proteolytic enzymes, which may have antimicrobial properties. We identified a second method by which P. piscicida kills V. parahaemolyticus It involves the direct transfer of apparently lytic vesicles from the surface of the Pseudoalteromonas strains to the surface of Vibrio cells, with subsequent digestion of holes in the Vibrio cell walls. Enzymes associated with these vesicles are likely responsible for the digestion of holes in the cell walls. Pseudoalteromonas piscicida has potential applications in aquaculture and food safety, in control of the formation of biofilms in the environment, and in food processing. These findings may facilitate the probiotic use of P. piscicida to inactivate pathogens and may lead to the isolation of enzymes and other antimicrobial compounds of pharmacological value.

Helicobacter pylori-derived extracellular vesicles increased in the gastric juices of gastric adenocarcinoma patients and induced inflammation mainly via specific targeting of gastric epithelial cells

Evidence indicates that Helicobacter pylori is the causative agent of chronic gastritis and perhaps gastric malignancy. Extracellular vesicles (EVs) play an important role in the evolutional process of malignancy due to their genetic material cargo. We aimed to evaluate the clinical significance and biological mechanism of H. pylori EVs on the pathogenesis of gastric malignancy. We performed 16S rDNA-based metagenomic analysis of gastric juices either from endoscopic or surgical patients. From each sample of gastric juices, the bacteria and EVs were isolated. We evaluated the role of H. pylori EVs on the development of gastric inflammation in vitro and in vivo. IVIS spectrum and confocal microscopy were used to examine the distribution of EVs. The metagenomic analyses of the bacteria and EVs showed that Helicobacter and Streptococcus are the two major bacterial genera, and they were significantly increased in abundance in gastric cancer (GC) patients. H. pylori EVs are spherical and contain CagA and VacA. They can induce the production of tumor necrosis factor-α, interleukin (IL)-6 and IL-1β by macrophages, and IL-8 by gastric epithelial cells. Also, EVs induce the expression of interferon gamma, IL-17 and EV-specific immunoglobulin Gs in vivo in mice. EVs were shown to infiltrate and remain in the mouse stomach for an extended time. H. pylori EVs, which are abundant in the gastric juices of GC patients, can induce inflammation and possibly cancer in the stomach, mainly via the production of inflammatory mediators from gastric epithelial cells after selective uptake by the cells.

Achieving the Promise of Therapeutic Extracellular Vesicles: The Devil is in Details of Therapeutic Loading

Extracellular vesicles (EVs) represent a class of cell secreted organelles which naturally contain biomolecular cargo such as miRNA, mRNA and proteins. EVs mediate intercellular communication, enabling the transfer of functional nucleic acids from the cell of origin to the recipient cells. In addition, EVs make an attractive delivery vehicle for therapeutics owing to their increased stability in circulation, biocompatibility, low immunogenicity and toxicity profiles. EVs can also be engineered to display targeting moieties on their surfaces which enables targeting to desired tissues, organs or cells. While much has been learned on the role of EVs as cell communicators, the field of therapeutic EV application is currently under development. Critical to the future success of EV delivery system is the description of methods by which therapeutics can be successfully and efficiently loaded within the EVs. Two methods of loading of EVs with therapeutic cargo exist, endogenous and exogenous loading. We have therefore focused this review on describing the various published approaches for loading EVs with therapeutics.

Urinary extracellular vesicles. A promising shortcut to novel biomarker discoveries

Proteomic and genomic techniques have reached full maturity and are providing unforeseen details for the comprehensive understanding of disease pathologies at a fraction of previous costs. However, for kidney diseases, many gaps in such information remain to inhibit major advances in the prevention, treatment and diagnostics of these devastating diseases, which have enormous global impact. The discovery of ubiquitous extracellular vesicles (EV) in all bodily fluids is rapidly increasing the fundamental knowledge of disease mechanisms and the ways in which cells communicate with distant locations in processes of cancer spread, immunological regulation, barrier functions and general modulation of cellular activity. In this review, we describe some of the most prominent research streams and findings utilizing urinary extracellular vesicles as highly versatile and dynamic tools with their extraordinary protein and small regulatory RNA species. While being a highly promising approach, the relatively young field of EV research suffers from a lack of adherence to strict standardization and carefully scrutinized methods for obtaining fully reproducible results. With the appropriate guidelines and standardization achieved, urine is foreseen as forming a unique, robust and easy route for determining accurate and personalized disease signatures and as providing highly useful early biomarkers of the disease pathology of the kidney and beyond.

Analysis and Characterization of Proteins Associated with Outer Membrane Vesicles Secreted by Cronobacter spp

Little is known about secretion of outer membrane vesicles (OMVs) by Cronobacter. In this study, OMVs isolated from Cronobacter sakazakii, Cronobacter turicensis, and Cronobacter malonaticus were examined by electron microscopy (EM) and their associated outer membrane proteins (OMP) and genes were analyzed by SDS-PAGE, protein sequencing, BLAST, PCR, and DNA microarray. EM of stained cells revealed that the OMVs are secreted as pleomorphic micro-vesicles which cascade from the cell's surface. SDS-PAGE analysis identified protein bands with molecular weights of 18 kDa to >100 kDa which had homologies to OMPs such as GroEL; OmpA, C, E, F, and X; MipA proteins; conjugative plasmid transfer protein; and an outer membrane auto-transporter protein (OMATP). PCR analyses showed that most of the OMP genes were present in all seven Cronobacter species while a few genes (OMATP gene, groEL, ompC, mipA, ctp, and ompX) were absent in some phylogenetically-related species. Microarray analysis demonstrated sequence divergence among the OMP genes that was not captured by PCR. These results support previous findings that OmpA and OmpX may be involved in virulence of Cronobacter, and are packaged within secreted OMVs. These results also suggest that other OMV-packaged OMPs may be involved in roles such as stress response, cell wall and plasmid maintenance, and extracellular transport.

Emergent properties of extracellular vesicles: a holistic approach to decode the complexity of intercellular communication networks

Holistic approaches to decode emergent properties of extracellular vesicles either at a single vesicle level or at a systems level.

Bacterial RNA as a signal to eukaryotic cells as part of the infection process

The discovery of regulatory RNA has identified an underappreciated area for microbial subversion of the host. There is increasing evidence that RNA can be delivered from bacteria to host cells associated with membrane vesicles or by direct release from intracellular bacteria. Once inside the host cell, RNA can act by activating sequence-independent receptors of the innate immune system, where recent findings suggest this can be more than simple pathogen detection, and may contribute to the subversion of immune responses. Sequence specific effects are also being proposed, with examples from nematode, plant and human models providing support for the proposition that bacteria-to-human RNA signaling and the subversion of host gene expression may occur.

Extracellular vesicle mimetics: Novel alternatives to extracellular vesicle-based theranostics, drug delivery, and vaccines

Extracellular vesicles are nano-sized spherical bilayered proteolipids encasing various components. Cells of all domains of life actively release these vesicles to the surroundings including various biological fluids. These extracellular vesicles are known to play pivotal roles in numerous pathophysiological functions. Extracellular vesicles have distinct characteristics, like high biocompatibility, safety, and nano-sized diameters that allow efficient drug loading capacity and long blood circulation half-life. These characteristics of extracellular vesicles have engrossed many scientists to harness them as new tools for novel delivery systems. This review will highlight the current state of the arts and problems of such extracellular vesicle-based theranostics, drug delivery and vaccines, and introduce "extracellular vesicle mimetics" as the novel alternative of extracellular vesicles. We hope to provide insights into the potential of extracellular vesicle mimetics as superior substitute to the natural extracellular vesicles that can be applied to theranostics, drug delivery, and vaccines against various diseases.

Interspecies Communication between Pathogens and Immune Cells via Bacterial Membrane Vesicles

The production of extracellular vesicles is a universal mechanism for intercellular communication that is conserved across kingdoms. Prokaryotes secrete 50–250 nm membrane vesicles (MVs) in a manner that is regulated by environmental stress and is thought to promote survival. Since many types of host-derived stress are encountered during infection, this implies an important role for MV secretion in bacterial pathogenesis. Accordingly, MVs produced by gram-positive and gram-negative pathogens contain toxins, virulence factors, and other molecules that promote survival in the host. However, recent studies have also shown that bacterial MVs are enriched for molecules that stimulate innate and adaptive immune responses. As an example, MVs may serve multiple, important roles in regulating the host response to Mycobacterium tuberculosis (Mtb), an intracellular pathogen that infects lung macrophages and resides within modified phagosomes. Previously, we demonstrated that Mtb secretes MVs during infection that may modulate infected and uninfected immune cells. Our present data demonstrates that Mtb MVs inhibit the functions of macrophages and T cells, but promote Major Histocompatibility Complex (MHC) class II antigen presentation by dendritic cells. We conclude that bacterial MVs serve dual and opposing roles in the activation of and defense against host immune responses to Mtb and other bacterial pathogens. We also propose that MV secretion is a central mechanism for interspecies communication between bacteria and host cells during infection.

Extracellular Vesicles in Chronic Obstructive Pulmonary Disease

Chronic obstructive pulmonary disease (COPD) is characterized by the progression of irreversible airflow limitation and is a leading cause of morbidity and mortality worldwide. Although several crucial mechanisms of COPD pathogenesis have been studied, the precise mechanism remains unknown. Extracellular vesicles (EVs), including exosomes, microvesicles, and apoptotic bodies, are released from almost all cell types and are recognized as novel cell–cell communication tools. They have been shown to carry and transfer a wide variety of molecules, such as microRNAs, messenger RNAs, and proteins, which are involved in physiological functions and the pathology of various diseases. Recently, EVs have attracted considerable attention in pulmonary research. In this review, we summarize the recent findings of EV-mediated COPD pathogenesis. We also discuss the potential clinical usefulness of EVs as biomarkers and therapeutic agents for the treatment of COPD.