Probiotic Escherichia coli Nissle 1917-derived outer membrane vesicles enhance immunomodulation and antimicrobial activity in RAW264.7 macrophages

Effect of the probiotic Escherichia coli Nissle 1917 on serum levels of NADPH oxidase-2 and lipopolysaccharide in patients with Alzheimer's disease

BackgroundIntestinal bacteria-derived molecules, such as lipopolysaccharide (LPS) produced by Gram-negative bacteria, can translocate into the bloodstream through the gut wall, contributing to inflammation and neurodegeneration via oxidative stress mechanisms. NADPH oxidase-2 activation and superoxide anion production play a key role in this process, particularly in conditions like Alzheimer's disease (AD), where gut permeability is often altered. This study hypothesized that modulating gut microbiota with the probiotic Escherichia coli Nissle 1917 (ECN) could mitigate LPS translocation and its associated inflammatory effects.ObjectiveTo evaluate the effect of daily ECN administration on serum LPS levels in elderly AD patients.MethodsA randomized, double-blind, placebo-controlled trial was conducted with 40 mild AD patients, with 39 completing the study (20 ECN, 19 placebo). Participants received ECN (2.5-25 × 10^9 CFU/capsule) or placebo for six weeks. The serum activity of soluble NOX2-dp (sNOX2-dp), hydrogen peroxide (H2O2) production, tumor necrosis factor (TNF)-α levels and LPS was evaluated, while serum zonulin levels were measured to assess gut permeability.ResultsThe ECN group showed significant reductions in sNOX2-dp (-21%), H2O2 (-27%), TNF-α (-18%), LPS (-15%), and zonulin (-35%), along with improved Mini-Mental State Examination (MMSE) scores. No significant changes were seen in the placebo group. Mixed ANOVA showed significant time-by-treatment interactions for zonulin (p = 0.04) and MMSE (p < 0.001). Changes in LPS correlated with changes in zonulin (Rs = 0.408, p = 0.011).ConclusionsECN may strengthen gut barrier function, reduce endotoxemia, and attenuate inflammation in AD, though larger studies are needed to confirm these findings.

The biological activity and potential of probiotics-derived extracellular vesicles as postbiotics in modulating microbiota-host communication

Probiotics such as Lactobacillus and Bifidobacterium spp. have been shown to be critical for maintaining host homeostasis. In recent years, key compounds of postbiotics derived from probiotic metabolism and cellular secretion have been identified for their role in maintaining organ immunity and regulating intestinal inflammation. In particular, probiotic-derived extracellular vesicles (PEVs) can act as postbiotics, maintaining almost the same functional activity as probiotics. They also have strong biocompatibility and loading capacity to carry exogenous or parental active molecules to reach distal organs to play their roles. This provides a new direction for understanding the intrinsic microbiota-host communication mechanism. However, most current studies on PEVs are limited to their functional effects/benefits, and their specific physicochemical properties, composition, intrinsic mechanisms for maintaining host homeostasis, and possible threats remain to be explored. Here, we review and summarize the unique physicochemical properties of PEVs and their bioactivities and mechanisms in mediating microbiota-host communication, and elucidate the limitations of the current research on PEVs and their potential application as postbiotics.

Separation and Characterization of Heterogeneity Among Various Sizes of Outer Membrane Vesicles Derived from the Probiotic Escherichia coli Nissle 1917

Outer membrane vesicles (OMVs) are extracellular vesicles secreted by Gram-negative bacteria with diameters of 20-250 nm. OMVs contain various biologically active substances from their parent bacteria, such as proteins, lipids, and nucleic acids. Escherichia coli Nissle 1917 (EcN) is a Gram-negative probiotic that resides in the human intestine. EcN-derived OMVs are pivotal in modulating intestinal immune responses. However, few studies have addressed the heterogeneity of EcN-derived OMVs in terms of size, significantly limiting the research on their clinical applications. Currently, there are a lack of feasible methods for obtaining EcN-derived OMVs of different sizes. To address this knowledge gap, we developed a membrane filtration method to isolate EcN-derived OMVs of varying sizes. In this study, we first used gradient filtration to isolate high-purity EcN-derived OMVs and conducted a proteomic analysis. Subsequently, we used membrane filtration to separate the EcN-derived OMVs by size. We successfully obtained EcN-derived OMVs of three specific sizes: <50 nm, 50-100 nm, and 100-300 nm. We then performed proteomic analyses of these EcN-derived OMVs and compared their protein profiles. Finally, we compared the ability of each EcN-derived OMV type to induce RAW264.7 macrophages to secrete the pro-inflammatory factor interleukin (IL)-1β and the anti-inflammatory factor IL-10. The EcN-derived OMVs contained 646 different proteins overall; those of different sizes contained different protein types. Among them, the EcN-derived OMVs in the <50 nm group contained significantly fewer proteins (262 different types in total) than those in the 50-100 nm (1603 types) and 100-300 nm (1568 types) groups. Furthermore, the <50 nm group had fewer membrane proteins (40) than the 50-100 nm (215) and 100-300 nm (209) groups. We also found that RAW264.7 macrophages secreted different concentrations of IL-1β and IL-10 following co-incubation with the three EcN-derived OMV types. The 50-100 nm EcN-derived OMV group showed a stronger effect in terms of inducing inflammatory cytokine secretion compared to the other two groups. This study provides direct experimental evidence that EcN-derived OMVs of different sizes exhibit heterogeneous properties.

Linking microbial communities to rheumatoid arthritis: focus on gut, oral microbiome and their extracellular vesicles

Rheumatoid arthritis (RA) is a severe, chronic autoimmune disease affecting approximately 1% of the global population. Research has demonstrated that microorganisms play a crucial role in the onset and progression of RA. This indicates that the disruption of immune homeostasis may originate from mucosal sites, such as the gut and oral cavity. In the intestines of patients in the preclinical stage of RA, an increased abundance of Prevotella species with a strong association to the disease was observed. In the oral cavity, infections by Porphyromonas gingivalis and Aggregatibacter actinomycetemcomitans can mediate the production of anti-citrullinated protein antibodies (ACPAs), potentially contributing to RA pathogenesis. Nevertheless, no single bacterial species has been consistently identified as the primary driver of RA. This review will discuss the connection between gut and oral bacteria in the development of arthritis. Additionally, it explores the role of bacterial extracellular vesicles (bEVs) in inducing inflammation and their potential pathogenic roles in RA.

The Therapeutic Potential of Exosome Therapy in Sepsis Management: Addressing Complications and Improving Outcomes"

Infection occurs when pathogens penetrate tissues, reproduce, and trigger a host response to both the infectious agents and their toxins. A diverse array of pathogens, including viruses and bacteria, can cause infections. The host's immune system employs several mechanisms to combat these infections, typically involving an innate inflammatory response. Inflammation is a complex biological reaction that can affect various parts of the body and is a key component of the response to harmful stimuli. Sepsis arises when the body's response to infection leads to widespread damage to tissues and organs, potentially resulting in severe outcomes or death. The initial phase of sepsis involves immune system suppression. Early identification and targeted management are crucial for improving sepsis outcomes. Common treatment approaches include antibiotics, intravenous fluids, blood cultures, and monitoring urine output. This study explores the potential of exosome therapy in enhancing the management and alleviation of sepsis symptoms.

Bifidobacterium longum NSP001-derived extracellular vesicles ameliorate ulcerative colitis by modulating T cell responses in gut microbiota-(in)dependent manners

Recent studies have shown that intestinal commensal bacteria-derived vesicles may have potential effects in alleviating ulcerative colitis (UC). Although Bifidobacterium longum is widely used to prevent colitis, the potential role of B. longum-derived extracellular vesicles has yet to be explored. Here, we extracted B. longum NSP001-derived extracellular vesicles (NEVs) and investigated the regulatory roles of NEVs in colitis. Our results demonstrated that NEVs alleviate UC by improving intestinal barrier, modulating immune cell differentiation, and promoting the production of SCFAs. NEVs' improvement of inflammation in pseudo-germ-free mice implies that the anti-inflammatory effect of NEVs does not exclusively depend on the regulation of gut microbiota. In conclusion, we suggest that B. longum NSP001 improves UC through the secretion of NEVs. In addition, the study emphasizes the critical role of NEVs in maintaining host immune homeostasis via suppressing STAT3 pathway, thereby highlighting their potential as a novel postbiotic to alleviate UC.

Pathogenic and therapeutic roles of extracellular vesicles in sepsis

Sepsis is a systemic injury resulting in vascular dysfunction, which can lead to multiple organ dysfunction, even shock and death. Extracellular vesicles (EVs) released by mammalian cells and bacteria have been shown to play important roles in intercellular communication and progression of various diseases. In past decades, the functional role of EVs in sepsis and its complications has been well explored. EVs are one of the paracrine components of cells. By delivering bioactive materials, EVs can promote immune responses, particularly the development of inflammation. In addition, EVs can serve as beneficial tools for delivering therapeutic cargos. In this review, we discuss the dual role of EVs in the progression and treatment of sepsis, exploring their intricate involvement in both inflammation and tissue repair processes. Specifically, the remarkable role of engineered strategies based on EVs in the treatment of sepsis is highlighted. The engineering EVs-mediated drug delivery and release strategies offer broad prospects for the effective treatment of sepsis. EVs-based approaches provide a novel avenue for diagnosing sepsis and offer opportunities for more precise intervention.

Characterization of Extracellular Vesicles from Streptococcus thermophilus 065 and Their Potential to Modulate the Immune Response

Bacteria can release membrane-derived nanoparticles made of lipid bilayers, so-called extracellular vesicles (EVs), which can carry diverse cargo and are important for microbe-microbe and microbe-host interactions. Here, we studied the production of EVs by Streptococcus thermophilus 065, the protein composition of the EVs, and how the produced EVs impact the immune response in vitro. Cultures of S. thermophilus grown for 6 h at 40 °C in M17 broth with 2% lactose reached high biomass yields and a high level of EVs quantified by lipophilic fluorescent dye staining. Proteome analysis of the isolated EVs revealed a high abundance of membrane-associated binding proteins of ABC transporters, ribosomal proteins, and glycolytic enzymes. In addition, phage proteins were found to be present in the EVs, which suggests a low-level expression of prophage genes during growth most likely supporting the release of EVs without causing cell lysis. The role of prophage activation was confirmed in an experiment with the addition of mitomycin C resulting in the expression of phage proteins including holin and endolysin causing a drop in culture OD and concomitant EV release. Subsequent in vitro immune assays using non-activated and activated human peripheral blood mononuclear cells (PBMCs) showed immune regulation in both cases upon exposure to S. thermophilus EVs and producer cells. This study shows the capacity of S. thermophilus EVs to act as immune modulators and opens the possibility for their use as postbiotics.

Probiotic bacteria-released extracellular vesicles enhance macrophage phagocytosis in polymicrobial sepsis by activating the FPR1/2 pathway

BACKGROUND

Sepsis-induced organ failure and high mortality are largely ascribed to the failure of bacterial clearance from the infected tissues. Recently, probiotic bacteria-released extracellular vesicles (BEVs) have been implicated as critical mediators of intercellular communication which are widely involved in the regulation of the inflammatory response. However, their functional role in macrophage phagocytosis during sepsis has never been explored.

METHODS

BEVs were collected from three different strains of probiotics including Lactiplantibacillus plantarum WCFS1 (LP WCFS1), Lactobacillus rhamnosus Gorbach-Goldin (LGG), and Escherichia coli Nissle 1917 (EcN), or from LGG cultured under three pH conditions (pH5-acid, pH6.5-standard, pH8-akaline) through differential centrifugation, filtration, and ultracentrifugation of their culture supernatants. In vitro phagocytosis was measured in Raw264.7 cells and bone marrow-derived macrophages using pHrodo red E. coli BioParticles. The in vivo therapeutic effects of BEVs were tested using a feces-injection-in-peritoneum (FIP) model of polymicrobial sepsis.

RESULTS

LGG-derived EVs (BEVLGG) were the best among these three probiotics BEVs in stimulating macrophages to take up bacteria. Furthermore, BEVLGG collected from pH8 culture condition (BEVpH8) exhibited the strongest capacity of phagocytosis, compared with BEVpH5 and BEVpH6.5. Treatment of septic mice with BEVpH8 significantly prolonged animal survival; increased bacterial clearance from the blood, peritoneal lavage fluid, and multiple organs; and decreased serum levels of pro-inflammatory cytokines/chemokines, as well as reduced multiple organ injuries, in comparison with control-treated septic mice. Mechanistically, RNA-seq and bioinformatic analysis identified that the FPR1/2 signaling was remarkably activated, along with its downstream pathways (PI3K-Akt-MARCO and NADPH-ROS) in BEVpH8-treated macrophages, compared with control cells. Accordingly, pre-addition of Boc2, a specific antagonist of FPR1/FPR2, to macrophages significantly attenuated BEVpH8-mediated phagocytosis, compared to controls.

CONCLUSIONS

This study demonstrates that LGG-derived BEVs may have therapeutic effects against sepsis-induced organ injury and mortality through enhancing FPR1/2-mediated macrophage phagocytosis.

Microscopic messengers: microbiota-derived bacterial extracellular vesicles in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a persistent and complex condition accomplished by inflammation of the gastrointestinal system, encompassing Crohn's disease (CD) and ulcerative colitis (UC). This condition is caused by the combination of genetic predispositions, environmental triggers, and dysregulated immunological responses, which complicates diagnosis and treatment. The latest developments in gastroenterology have revealed the critical significance of the gut microbiota in the pathogenesis of IBD. Extracellular vesicles (EVs) are a type of microbial component that potentially regulate intestinal inflammation. The impact of microbiota-derived bacterial EVs (bEVs) on intestinal inflammation is mediated through several methods. They can intensify inflammation or stimulate defensive responses by delivering immunomodulatory cargo. Improved comprehension could enhance inventive diagnostic and treatment strategies for IBD. This study aimed to explore the relationship between microbiota-derived bEVs and the complex nature of IBD. We performed a thorough analysis of the formation, composition, mechanisms of action, diagnostic possibilities, therapeutic implications, and future prospects of these microbiota-derived bEVs.

Role of probiotic extracellular vesicles in inter-kingdom communication and current technical limitations in advancing their therapeutic utility

Diverse functions of probiotic extracellular vesicles (EVs) have been extensively studied over the past decade, proposing their role in inter-kingdom communication. Studies have explored their therapeutic role in pathophysiological processes ranging from cancer, immunoregulation, and ulcerative colitis to stress-induced depression. These studies have highlighted the significant and novel potential of probiotic EVs for therapeutic applications, offering immense promise in addressing several unmet clinical needs. Additionally, probiotic EVs are being explored as vehicles for targeted delivery approaches. However, the realization of clinical utility of probiotic EVs is hindered by several knowledge gaps, pitfalls, limitations, and challenges, which impede their wider acceptance by the scientific community. Among these, limited knowledge of EV biogenesis, markers and regulators in bacteria, variations in cargo due to culture conditions or EV isolation method, and lack of proper understanding of gut uptake and demonstration of in vivo effect are some important issues. This review aims to summarize the diverse roles of probiotic EVs in health and disease conditions. More importantly, it discusses the significant knowledge gaps and limitations that stand in the way of the therapeutic utility of probiotic EVs. Furthermore, the importance of addressing these gaps and limitations with technical advances such as rigorous omics has been discussed.

Immunomodulatory Effects of Probiotic-Derived Extracellular Vesicles: Opportunities and Challenges

Probiotics are known to modulate host immune responses in the course of many diseases. Recently, bacterial extracellular vesicles (EVs), which contain bioactive proteins, lipids, nucleic acids, and metabolites released by bacteria, have been identified as potentially important mediators of bacteria-bacterium and bacteria-host interactions. With the deepening of research, it has been found that probiotic-derived EVs play a significant role in regulating host immune function and, thus, exerting health-promoting effects. Nevertheless, current research is in its early stages, and there remains a long way to go to bridge the gap between basic research and clinical practice. In this review, we describe the fundamental aspects of probiotic-derived EVs, including their biogenesis, cargo sorting mechanism, and transport capabilities. We further discussed the potential mechanisms of probiotic-derived EVs in regulating the host's gut microbiota and immune responses. Finally, we speculate about the potential of probiotic-derived EVs as new postbiotics for applications in functional food, disease treatment substitutes, and immune regulatory adjuvants.

Proteomic Analysis of Caco-2 Cells Disrupted by EcN 1917-Derived OMVs Reveals Molecular Information on Bacteria-Mediated Cancer Cell Migration

Escherichia coli Nissle 1917 (EcN 1917) exhibits distinct tumor-targeting activity, and early studies demonstrated that outer membrane vesicles (OMVs) mediate bacteria-host interactions. To decipher the molecular mechanism underlying the interaction between EcN 1917 and host cells via OMV-mediated communication, we investigated the phenotypic changes in Caco-2 cells perturbed by EcN 1917-derived OMVs and constructed proteomic maps of the EcN 1917-derived OMV components and OMV-perturbed host cells. Our findings revealed that the size of the EcN 1917-derived OMV proteome increased 4-fold. Treatment with EcN 1917-derived OMVs altered the proteomic and phosphoproteomic profiles of host cells. Importantly, for the first time, we found that treatment with EcN 1917-derived OMVs inhibited cancer cell migration by suppressing the expression of ANXA9. In addition, phosphoproteomic data suggested that the ErbB pathway may be involved in OMV-mediated cell migration. Taken together, our study provides valuable data for further investigations of OMV-mediated bacteria-host interactions and offers great insights into the underlying mechanism of probiotic-assisted colorectal cancer therapy.

Efficient Isolation of Outer Membrane Vesicles (OMVs) Secreted by Gram-Negative Bacteria via a Novel Gradient Filtration Method

Bacterial extracellular vesicles (bEVs) secreted by Gram-negative bacteria are referred to as outer membrane vesicles (OMVs) because they originate in the outer membrane. OMVs are membrane-coated vesicles 20-250 nm in size. They contain lipopolysaccharide (LPS), peptidoglycan, proteins, lipids, nucleic acids, and other substances derived from their parent bacteria and participate in the transmission of information to host cells. OMVs have broad prospects in terms of potential application in the fields of adjuvants, vaccines, and drug delivery vehicles. Currently, there remains a lack of efficient and convenient methods to isolate OMVs, which greatly limits OMV-related research. In this study, we developed a fast, convenient, and low-cost gradient filtration method to separate OMVs that can achieve industrial-scale production while maintaining the biological activity of the isolated OMVs. We compared the gradient filtration method with traditional ultracentrifugation to isolate OMVs from probiotic Escherichia coli Nissle 1917 (EcN) bacteria. Then, we used RAW264.7 macrophages as an in vitro model to study the influence on the immune function of EcN-derived OMVs obtained through the gradient filtration method. Our results indicated that EcN-derived OMVs were efficiently isolated using our gradient filtration method. The level of OMV enrichment obtained via our gradient filtration method was about twice as efficient as that achieved through traditional ultracentrifugation. The EcN-derived OMVs enriched through the gradient filtration method were successfully taken up by RAW264.7 macrophages and induced them to secrete pro-inflammatory cytokines such as tumor necrosis factor α (TNF-α) and interleukins (ILs) 6 and 1β, as well as anti-inflammatory cytokine IL-10. Furthermore, EcN-derived OMVs induced more anti-inflammatory response (i.e., IL-10) than pro-inflammatory response (i.e., TNF-α, IL-6, and IL-1β). These results were consistent with those reported in the literature. The related literature reported that EcN-derived OMVs obtained through ultracentrifugation could induce stronger anti-inflammatory responses than pro-inflammatory responses in RAW264.7 macrophages. Our simple and novel separation method may therefore have promising prospects in terms of applications involving the study of OMVs.

Influences of bacterial extracellular vesicles on macrophage immune functions

Bacterial extracellular vesicles (EVs) are crucial mediators of information transfer between bacteria and host cells. Macrophages, as key effector cells in the innate immune system, have garnered widespread attention for their interactions with bacterial EVs. Increasing evidence indicates that bacterial EVs can be internalized by macrophages through multiple pathways, thereby influencing their immune functions. These functions include inflammatory responses, antimicrobial activity, antigen presentation, and programmed cell death. Therefore, this review summarizes current research on the interactions between bacterial EVs and macrophages. This will aid in the deeper understanding of immune modulation mediated by pathogenic microorganisms and provide a basis for developing novel antibacterial therapeutic strategies.

Unveiling clinical applications of bacterial extracellular vesicles as natural nanomaterials in disease diagnosis and therapeutics

Bacterial extracellular vesicles (BEVs) are naturally occurring bioactive membrane-bound nanoparticles released by both gram-negative and gram-positive bacterial species, exhibiting a multifaceted role in mediating host-microbe interactions across various physiological conditions. Increasing evidence supports BEVs as essential mediators of cell-to-cell communicaiton, influencing bacterial pathogenicity, disease mechanisms, and modulating the host immune response. However, the extent to which these BEV-mediated actions can be leveraged to predict disease onset, guide treatment strategies, and determine clinical outcomes remains uncertain, particularly in terms of their clinical translation potentials. This review briefly describes BEV biogenesis and their internalisation by recipient cells and summarises methods for isolation and characterization, essential for understanding their composition and cargo. Further, it discusses the potential of biofluid-associated BEVs as biomarkers for various diseases, spanning both cancer and non-cancerous conditions. Following this, we outline the ongoing human clinical trials of using BEVs for vaccine development. In addition to disease diagnostics, this review explores the emerging research of using natural or engineered BEVs as smart nanomaterials for applications in anti-cancer therapy and bone regeneration. This discussion extends to key factors for unlocking the clinical potential of BEVs, such as standardization of BEV isolation and characterisation, as well as other hurdles in translating these findings to the clinical setting. We propose that addressing these hurdles through collaborative research efforts and well-designed clinical trials holds the key to fully harnessing the clinical potential of BEVs. As this field advances, this review suggests that BEV-based nanomedicine has the potential to revolutionize disease management, paving the way for innovative diagnosis, therapeutics, and personalized medicine approaches. STATEMENT OF SIGNIFICANCE: Extracellular vesicles (EVs) from both host cells and bacteria serve as multifunctional biomaterials and are emerging in the fields of biomedicine, bioengineering, and biomaterials. However, the majority of current studies focus on host-derived EVs, leaving a gap in comprehensive research on bacteria-derived EVs (BEVs). Although BEVs offer an attractive option as nanomaterials for drug delivery systems, their unique nanostructure and easy-to-modify functions make them a potential method for disease diagnosis and treatment as well as vaccine development. Our work among the pioneering studies investigating the potential of BEVs as natural nanobiomaterials plays a crucial role in both understanding the development of diseases and therapeutic interventions.

The activation impact of lactobacillus-derived extracellular vesicles on lipopolysaccharide-induced microglial cell

Perioperative neurocognitive dysfunction (PND) emerges as a common postoperative complication among elderly patients. Currently, the mechanism of PND remains unclear, but there exists a tendency to believe that inflammation plays a significant role in PND. Alterations in the abundance of intestinal microbiota can increase the permeability of the intestinal mucosal barrier and incite extraintestinal inflammatory responses. Metabolites from these microbiota can be absorbed by the intestinal mucosa into the bloodstream, exerting influence upon the central nervous system (CNS). Lactobacillus (Lac), serving as an intestinal probiotic bacterium, possesses the capacity to modulate emotional behavior and cognitive functions. Extracellular vesicles (EVs) are recognized as novel therapeutic carriers for targeted delivery to regulate physiology and pathogenesis. While the mechanism governing the primary function of Lac-EVs in the CNS remains uncertain. Therefore, we established an in vitro neuroinflammation model to induce PND and then treated the mice with Lac-EVs to observe the effect of these EVs on neuroinflammation, particularly on microglial (MG) polarization. Our research unveils that Lac-EVs reduced inflammation induced by LPS in microglia and the activation of related proteins, including the mRNA expression of M1 labeled protein (iNOS). Moreover, the mRNA expression of M2-labeled protein (Arg1) increased. In addition, flow cytometry revealed that the ratio of M1/M2 microglia also changed significantly. Therefore, Lac-EVs promoted the differentiation of M2 microglia by inducing the preferential expression of specific markers related to M2 macrophages and inflammation. In terms of inflammatory cytokine expression, Lac-EVs decreased the secretion of proinflammatory cytokines (IL-1β and IL-6) and increased IL-10 production after lipopolysaccharide (LPS) stimulation. Therefore, Lac-EVs induce the activation of M2 microglial cells without inducing cellular harm in vitro, and they demonstrate anti-inflammatory effects against lipopolysaccharide-induced neuroinflammation. This finding suggested that it is an effective anti-inflammatory strategy for alleviating inflammation-driven PNDs.

BACTERIAL EXTRACELLULAR VESICLES IN THE REGULATION OF INFLAMMATORY RESPONSE AND HOST-MICROBE INTERACTIONS

ABSTRACT

Extracellular vesicles (EVs) are a new revelation in cross-kingdom communication, with increasing evidence showing the diverse roles of bacterial EVs (BEVs) in mammalian cells and host-microbe interactions. Bacterial EVs include outer membrane vesicles released by gram-negative bacteria and membrane vesicles generated from gram-positive bacteria. Recently, BEVs have drawn attention for their potential as biomarkers and therapeutic tools because they are nano-sized and can deliver bacterial cargo into host cells. Importantly, exposure to BEVs significantly affects various physiological and pathological responses in mammalian cells. Herein, we provide a comprehensive overview of the various effects of BEVs on host cells (i.e., immune cells, endothelial cells, and epithelial cells) and inflammatory/infectious diseases. First, the biogenesis and purification methods of BEVs are summarized. Next, the mechanisms and pathways identified by BEVs that stimulate either proinflammatory or anti-inflammatory responses are highlighted. In addition, we discuss the mechanisms by which BEVs regulate host-microbe interactions and their effects on the immune system. Finally, this review focuses on the contribution of BEVs to the pathogenesis of sepsis/septic shock and their therapeutic potential for the treatment of sepsis.

The Networked Interaction between Probiotics and Intestine in Health and Disease: A Promising Success Story

Probiotics are known to promote human health either precautionary in healthy individuals or therapeutically in patients suffering from certain ailments. Although this knowledge was empirical in past tomes, modern science has already verified it and expanded it to new limits. These microorganisms can be found in nature in various foods such as dairy products or in supplements formulated for clinical or preventive use. The current review examines the different mechanisms of action of the probiotic strains and how they interact with the organism of the host. Emphasis is put on the clinical therapeutic use of these beneficial microorganisms in various clinical conditions of the human gastrointestinal tract. Diseases of the gastrointestinal tract and particularly any malfunction and inflammation of the intestines seriously compromise the health of the whole organism. The interaction between the probiotic strains and the host's microbiota can alleviate the clinical signs and symptoms while in some cases, in due course, it can intervene in the underlying pathology. Various safety issues of the use of probiotics are also discussed.

Benefits and concerns of probiotics: an overview of the potential genotoxicity of the colibactin-producing Escherichia coli Nissle 1917 strain

Recently, the mounting integration of probiotics into human health strategies has gathered considerable attention. Although the benefits of probiotics have been widely recognized in patients with gastrointestinal disorders, immune system modulation, and chronic-degenerative diseases, there is a growing need to evaluate their potential risks. In this context, new concerns have arisen regarding the safety of probiotics as some strains may have adverse effects in humans. Among these strains, Escherichia coli Nissle 1917 (EcN) exhibited traits of concern due to a pathogenic locus in its genome that produces potentially genotoxic metabolites. As the use of probiotics for therapeutic purposes is increasing, the effects of potentially harmful probiotics must be carefully evaluated. To this end, in this narrative review article, we reported the findings of the most relevant in vitro and in vivo studies investigating the expanding applications of probiotics and their impact on human well-being addressing concerns arising from the presence of antibiotic resistance and pathogenic elements, with a focus on the polyketide synthase (pks) pathogenic island of EcN. In this context, the literature data here discussed encourages a thorough profiling of probiotics to identify potential harmful elements as done for EcN where potential genotoxic effects of colibactin, a secondary metabolite, were observed. Specifically, while some studies suggest EcN is safe for gastrointestinal health, conflicting findings highlight the need for further research to clarify its safety and optimize its use in therapy. Overall, the data here presented suggest that a comprehensive assessment of the evolving landscape of probiotics is essential to make evidence-based decisions and ensure their correct use in humans.

Bacterial membrane vesicles in the pathogenesis and treatment of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic and debilitating condition of relapsing and remitting inflammation in the gastrointestinal tract. Conventional therapeutic approaches for IBD have shown limited efficacy and detrimental side effects, leading to the quest for novel and effective treatment options for the disease. Bacterial membrane vesicles (MVs) are nanosized lipid particles secreted by lysis or blebbing processes from both Gram-negative and Gram-positive bacteria. These vesicles, known to carry bioactive components, are facsimiles of the parent bacterium and have been implicated in the onset and progression, as well as in the amelioration of IBD. This review discusses the overview of MVs and their impact in the pathogenesis, diagnosis, and treatment of IBD. We further discuss the technical challenges facing this research area and possible research questions addressing these challenges. We summarize recent advances in the diverse relationship between IBD and MVs, and the application of this knowledge as a viable and potent therapeutic strategy for IBD.

Effect of Extracelluar Vesicles Derived from Akkermansia muciniphila on Intestinal Barrier in Colitis Mice

Inflammatory bowel disease (IBD) is a chronic and recurrent disease. It has been observed that the incidence and prevalence of IBD are increasing, which consequently raises the risk of developing colon cancer. Recently, the regulation of the intestinal barrier by probiotics has become an effective treatment for colitis. Akkermansia muciniphila-derived extracellular vesicles (Akk EVs) are nano-vesicles that contain multiple bioactive macromolecules with the potential to modulate the intestinal barrier. In this study, we used ultrafiltration in conjunction with high-speed centrifugation to extract Akk EVs. A lipopolysaccharide (LPS)-induced RAW264.7 cell model was established to assess the anti-inflammatory effects of Akk EVs. It was found that Akk EVs were able to be absorbed by RAW264.7 cells and significantly reduce the expression of nitric oxide (NO), TNF-α, and IL-1β (p < 0.05). We explored the preventative effects on colitis and the regulating effects on the intestinal barrier using a mouse colitis model caused by dextran sulfate sodium (DSS). The findings demonstrated that Akk EVs effectively prevented colitis symptoms and reduced colonic tissue injury. Additionally, Akk EVs significantly enhanced the effectiveness of the intestinal barrier by elevating the expression of MUC2 (0.53 ± 0.07), improving mucus integrity, and reducing intestinal permeability (p < 0.05). Moreover, Akk EVs increased the proportion of the beneficial bacteria Firmicutes (33.01 ± 0.09%) and downregulated the proportion of the harmful bacteria Proteobacteria (0.32 ± 0.27%). These findings suggest that Akk EVs possess the ability to regulate immune responses, protect intestinal barriers, and modulate the gut microbiota. The research presents a potential intervention approach for Akk EVs to prevent colitis.

High performance anion exchange chromatography purification of probiotic bacterial extracellular vesicles enhances purity and anti-inflammatory efficacy

Bacterial extracellular vesicles (BEVs), including outer membrane vesicles, have emerged as a promising new class of vaccines and therapeutics to treat cancer and inflammatory diseases, among other applications. However, clinical translation of BEVs is hindered by a current lack of scalable and efficient purification methods. Here, we address downstream BEV biomanufacturing limitations by developing a method for orthogonal size- and charge-based BEV enrichment using tangential flow filtration (TFF) in tandem with high performance anion exchange chromatography (HPAEC). The data show that size-based separation coisolated protein contaminants, whereas size-based TFF with charged-based HPAEC dramatically improved purity of BEVs produced by probiotic Gram-negative Escherichia coli and Gram-positive lactic acid bacteria (LAB). Escherichia coli BEV purity was quantified using established biochemical markers while improved LAB BEV purity was assessed via observed potentiation of anti-inflammatory bioactivity. Overall, this work establishes orthogonal TFF + HPAEC as a scalable and efficient method for BEV purification that holds promise for future large-scale biomanufacturing of therapeutic BEV products.

Extracellular vesicles of the probiotic bacteria E. coli O83 activate innate immunity and prevent allergy in mice

BACKGROUND

E. coli O83 (Colinfant Newborn) is a Gram-negative (G-) probiotic bacterium used in the clinic. When administered orally, it reduces allergic sensitisation but not allergic asthma. Intranasal administration offers a non-invasive and convenient delivery method. This route bypasses the gastrointestinal tract and provides direct access to the airways, which are the target of asthma prevention. G- bacteria such as E. coli O83 release outer membrane vesicles (OMVs) to communicate with the environment. Here we investigate whether intranasally administered E. coli O83 OMVs (EcO83-OMVs) can reduce allergic airway inflammation in mice.

METHODS

EcO83-OMVs were isolated by ultracentrifugation and characterised their number, morphology (shape and size), composition (proteins and lipopolysaccharide; LPS), recognition by innate receptors (using transfected HEK293 cells) and immunomodulatory potential (in naïve splenocytes and bone marrow-derived dendritic cells; BMDCs). Their allergy-preventive effect was investigated in a mouse model of ovalbumin-induced allergic airway inflammation.

RESULTS

EcO83-OMVs are spherical nanoparticles with a size of about 110 nm. They contain LPS and protein cargo. We identified a total of 1120 proteins, 136 of which were enriched in OMVs compared to parent bacteria. Proteins from the flagellum dominated. OMVs activated the pattern recognition receptors TLR2/4/5 as well as NOD1 and NOD2. EcO83-OMVs induced the production of pro- and anti-inflammatory cytokines in splenocytes and BMDCs. Intranasal administration of EcO83-OMVs inhibited airway hyperresponsiveness, and decreased airway eosinophilia, Th2 cytokine production and mucus secretion.

CONCLUSIONS

We demonstrate for the first time that intranasally administered OMVs from probiotic G- bacteria have an anti-allergic effect. Our study highlights the advantages of OMVs as a safe platform for the prophylactic treatment of allergy. Video Abstract.

Engineering Escherichia coli Nissle 1917 as a microbial chassis for therapeutic and industrial applications

Genetically engineered microbes, especially Escherichia coli, have been widely used in the biosynthesis of proteins and metabolites for medical and industrial applications. As a traditional probiotic with a well-established safety record, E. coli Nissle 1917 (EcN) has recently emerged as a microbial chassis for generating living therapeutics, drug delivery vehicles, and microbial platforms for industrial production. Despite the availability of genetic tools for engineering laboratory E. coli K-12 and B strains, new genetic engineering systems are still greatly needed to expand the application range of EcN. In this review, we have summarized the latest progress in the development of genetic engineering systems in EcN, as well as their applications in the biosynthesis and delivery of valuable small molecules and biomacromolecules of medical and/or industrial interest, followed by a glimpse of how this rapidly growing field will evolve in the future.

Probiotic Escherichia coli Nissle 1917-derived outer membrane vesicles modulate the intestinal microbiome and host gut-liver metabolome in obese and diabetic mice

Introduction

Obesity and diabetes are common chronic metabolic disorders which can cause an imbalance of the intestinal flora and gut-liver metabolism. Several studies have shown that probiotics, including Escherichia coli Nissle 1917 (EcN), promote microbial balance and metabolic health. However, there are no studies on how EcN outer membrane vesicles (EcN-OMVs) influence the intestinal microflora and affect the metabolic disorders of obesity and diabetes.

Methods

In this study, we evaluated the effects of EcN-OMVs on high-fat diet (HFD)-induced obesity and HFD + streptozotocin (STZ)-induced diabetes.

Results

EcN-OMVs could reduce body weight, decrease blood glucose, and increase plasma insulin in obese mice. Similarly, EcN-OMVs treatment could modify the ratio of Firmicutes/Bacteroidetes in the gut, elevate intestinal short-chain fatty acid (SCFA)-producing flora, and influence the SCFA content of the intestine. Furthermore, the intestinal metabolites ornithine and fumaric acid, hepatic ω-6 unsaturated fatty acids, and SCFAs were significantly increased after administering EcN-OMVs.

Discussion

Overall, this study showed that EcN-OMVs might act as post-biotic agents that could modulate gut-liver metabolism and ameliorate the pathophysiology of obesity and diabetes.

Inhibition of bacterial swimming by heparin binding of flagellin FliC from Escherichia coli strain Nissle 1917

Escherichia coli Nissle1917 (EcN) is a non-pathogenic probiotic strain widely used to maintain gut health, treat gastrointestinal disorders, and modulate the gut microbiome due to its anti-inflammatory and competitive exclusion effects against pathogenic bacteria. Heparin, abundant on intestinal mucosal surfaces, is a highly sulfated glycosaminoglycan primarily produced by mast cells. Currently, the interaction between EcN surface protein and heparin has remained elusive. In this study, the flagellin FliC responsible for EcN's movement was separated and characterized as a heparin binding protein by mass spectrometry (MS) analysis. The recombinant FliC protein, expressed by plasmid pET28a( +)-fliC, was further prepared to confirm the interaction between FliC and heparin. The results showed that heparin-Sepharose's ability to bind FliC was 48-fold higher than its ability to bind the negative control, bovine serum albumin (BSA). Neither the knockout of gene fliC nor the addition of heparin affects the growth of EcN, but both significantly inhibit the swimming of EcN. Adding 10 mg/ml heparin reduced the swimming diameter of the wild type and the complemented strain to 29-41% of the original, but that did not affect the swimming ability of the knockout strains. These results demonstrate that heparin interacts with EcN flagellin FliC and inhibits bacteria swimming. Exploring this interaction could improve our understanding of the relationship between hosts and microorganisms and provide a potential basis for disease treatment.

The use of a multicellular in vitro model to investigate uptake and migration of bacterial extracellular vesicles derived from the human gut commensal Bacteroides thetaiotaomicron

Bacterial extracellular vesicles (BEVs) are increasingly seen as key signalling mediators between the gut microbiota and the host. Recent studies have provided evidence of BEVs ability to transmigrate across cellular barriers to elicit responses in other tissues, such as the central nervous system (CNS). Here we use a combination of single-, two- and three-cell culture systems to demonstrate the transmigration of Bacteroides thetaiotaomicron derived BEVs (Bt-BEVs) across gut epithelium and blood brain barrier (BBB) endothelium, and their subsequent acquisition and downstream effects in neuronal cells. Bt-BEVs were shown to traffic to the CNS in vivo after intravenous administration to mice, and in multi-cell in vitro culture systems to transmigrate across gut epithelial and BBB endothelial cell barriers, where they were acquired by both microglia and immature neuronal cells. No significant activation/inflammatory effects were induced in non-differentiated neurons, in contrast to that observed in microglia cells, although this was notably less than that induced by lipopolysaccharide (LPS). Overall, our findings provide evidence for transmigration of Bt-BEVs across gut-epithelial and BBB endothelial cell barriers in vivo and in vitro, and their downstream responses in neural cells. This study sheds light onto how commensal bacteria-derived BEV transport across the gut-brain axis and can be exploited for the development of targeted drug delivery.

Diet, commensal microbiota-derived extracellular vesicles, and host immunity

The gut microbiota has co-evolved with its host, and commensal bacteria can influence both the host's immune development and function. Recently, a role has emerged for bacterial extracellular vesicles (BEVs) as potent immune modulators. BEVs are nanosized membrane vesicles produced by all bacteria, possessing the membrane characteristics of the originating bacterium and carrying an internal cargo that may include nucleic acid, proteins, lipids, and metabolites. Thus, BEVs possess multiple avenues for regulating immune processes, and have been implicated in allergic, autoimmune, and metabolic diseases. BEVs are biodistributed locally in the gut, and also systemically, and thus have the potential to affect both the local and systemic immune responses. The production of gut microbiota-derived BEVs is regulated by host factors such as diet and antibiotic usage. Specifically, all aspects of nutrition, including macronutrients (protein, carbohydrates, and fat), micronutrients (vitamins and minerals), and food additives (the antimicrobial sodium benzoate), can regulate BEV production. This review summarizes current knowledge of the powerful links between nutrition, antibiotics, gut microbiota-derived BEV, and their effects on immunity and disease development. It highlights the potential of targeting or utilizing gut microbiota-derived BEV as a therapeutic intervention.

The Two Faces of Bacterial Membrane Vesicles: Pathophysiological Roles and Therapeutic Opportunities

Bacterial membrane vesicles (MVs) are nanosized lipid particles secreted by lysis or blebbing mechanisms from Gram-negative and -positive bacteria. It is becoming increasingly evident that MVs can promote antimicrobial resistance but also provide versatile opportunities for therapeutic exploitation. As non-living facsimiles of parent bacteria, MVs can carry multiple bioactive molecules such as proteins, lipids, nucleic acids, and metabolites, which enable them to participate in intra- and interspecific communication. Although energetically costly, the release of MVs seems beneficial for bacterial fitness, especially for pathogens. In this review, we briefly discuss the current understanding of diverse MV biogenesis routes affecting MV cargo. We comprehensively highlight the physiological functions of MVs derived from human pathogens covering in vivo adaptation, colonization fitness, and effector delivery. Emphasis is given to recent findings suggesting a vicious cycle of MV biogenesis, pathophysiological function, and antibiotic therapy. We also summarize potential therapeutical applications, such as immunotherapy, vaccination, targeted delivery, and antimicrobial potency, including their experimental validation. This comparative overview identifies common and unique strategies for MV modification used along diverse applications. Thus, the review summarizes timely aspects of MV biology in a so far unprecedented combination ranging from beneficial function for bacterial pathogen survival to future medical applications.

Harnessing the potential of probiotics in the treatment of alcoholic liver disorders

In the current scenario, prolonged consumption of alcohol across the globe is upsurging an appreciable number of patients with the risk of alcohol-associated liver diseases. According to the recent report, the gut-liver axis is crucial in the progression of alcohol-induced liver diseases, including steatosis, steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Despite several factors associated with alcoholic liver diseases, the complexity of the gut microflora and its great interaction with the liver have become a fascinating area for researchers due to the high exposure of the liver to free radicals, bacterial endotoxins, lipopolysaccharides, inflammatory markers, etc. Undoubtedly, alcohol-induced gut microbiota imbalance stimulates dysbiosis, disrupts the intestinal barrier function, and trigger immune as well as inflammatory responses which further aggravate hepatic injury. Since currently available drugs to mitigate liver disorders have significant side effects, hence, probiotics have been widely researched to alleviate alcohol-associated liver diseases and to improve liver health. A broad range of probiotic bacteria like Lactobacillus, Bifidobacteria, Escherichia coli, Sacchromyces, and Lactococcus are used to reduce or halt the progression of alcohol-associated liver diseases. Several underlying mechanisms, including alteration of the gut microbiome, modulation of intestinal barrier function and immune response, reduction in the level of endotoxins, and bacterial translocation, have been implicated through which probiotics can effectively suppress the occurrence of alcohol-induced liver disorders. This review addresses the therapeutic applications of probiotics in the treatment of alcohol-associated liver diseases. Novel insights into the mechanisms by which probiotics prevent alcohol-associated liver diseases have also been elaborated.

Outer Membrane Vesicles (OMVs) as Biomedical Tools and Their Relevance as Immune-Modulating Agents against H. pylori Infections: Current Status and Future Prospects

Outer membrane vesicles (OMVs) are lipid-membrane-bounded nanoparticles that are released from Gram-negative bacteria via vesiculation of the outer membrane. They have vital roles in different biological processes and recently, they have received increasing attention as possible candidates for a broad variety of biomedical applications. In particular, OMVs have several characteristics that enable them to be promising candidates for immune modulation against pathogens, such as their ability to induce the host immune responses given their resemblance to the parental bacterial cell. Helicobacter pylori (H. pylori) is a common Gram-negative bacterium that infects half of the world's population and causes several gastrointestinal diseases such as peptic ulcer, gastritis, gastric lymphoma, and gastric carcinoma. The current H. pylori treatment/prevention regimens are poorly effective and have limited success. This review explores the current status and future prospects of OMVs in biomedicine with a special focus on their use as a potential candidate in immune modulation against H. pylori and its associated diseases. The emerging strategies that can be used to design OMVs as viable immunogenic candidates are discussed.

Extracellular Vesicles of Probiotics: Shedding Light on the Biological Activity and Future Applications

For many decades, the proper functioning of the human body has become a leading scientific topic. In the course of numerous experiments, a striking impact of probiotics on the human body has been documented, including maintaining the physiological balance of endogenous microorganisms, regulating the functioning of the immune system, enhancing the digestive properties of the host, and preventing or alleviating the course of many diseases. Recent research, especially from the last decade, shows that this health-benefiting activity of probiotics is largely conditioned by the production of extracellular vesicles. Although the importance of extracellular vesicles in the virulence of many live-threatening pathogens is widely described in the literature, much less is known with respect to the health-promoting effect of extracellular vesicles secreted by non-pathogenic microorganisms, including probiotics. Based on this, in the current review article, we decided to collect the latest literature data on the health-inducing properties of extracellular vesicles secreted by probiotics. The characteristics of probiotics' extracellular vesicles will be extended by the description of their physicochemical properties and the proteome in connection with the biological activities exhibited by these structures.

Desulfovibrio fairfieldensis-Derived Outer Membrane Vesicles Damage Epithelial Barrier and Induce Inflammation and Pyroptosis in Macrophages

Sulfate-reducing bacteria Desulfovibrio fairfieldensis is an opportunistic pathogen that widely exists in the human intestine and can cause severe infectious diseases. However, the mechanisms contributing to its pathogenesis remain of great interest. In this study, we aim to investigate the outer membrane vesicles (OMVs) secreted by D. fairfieldensis and their pathogenic effect. The OMVs separated by ultracentrifugation were spherical and displayed a characteristic bilayer lipid structure observed by transmission electron microscopy, with an average hydrodynamic diameter of 75 nm measurement using the particle size analyzer. We identified 1496 and 916 proteins from D. fairfieldensis and its OMVs using label-free non-target quantitative proteomics, respectively. The 560 co-expressed proteins could participate in bacterial life activities by function prediction. The translocation protein TolB, which participates in OMVs biogenesis and transporting toxins was highly expressed in OMVs. The OMVs inhibited the expression of tight junction proteins OCCLUDIN and ZO-1 in human colonic epithelial cells (Caco-2). The OMVs decreased the cell viability of monocyte macrophages (THP-1-Mφ) and activated various inflammatory factors secretion, including interferon-γ (IFN-γ), tumor necrosis factor (TNF-α), and many interleukins. Further, we found the OMVs induced the expression of cleaved-gasdermin D, caspase-1, and c-IL-1β and caused pyroptosis in THP-1-Mφ cells. Taken together, these data reveal that the D. fairfieldensis OMVs can damage the intestinal epithelial barrier and activate intrinsic inflammation.

Extracellular vesicle-mediated regulation of macrophage polarization in bacterial infections

Extracellular vesicles (EVs) are nanoscale membrane-enveloped vesicles secreted by prokaryotic and eukaryotic cells, which are commonly defined as membrane vesicles (MVs) and exosomes, respectively. They play critical roles in the bacteria-bacteria and bacteria-host interactions. In infectious diseases caused by bacteria, as the first line of defense against pathogens, the macrophage polarization mode commonly determines the success or failure of the host's response to pathogen aggression. M1-type macrophages secrete pro-inflammatory factors that support microbicidal activity, while alternative M2-type macrophages secrete anti-inflammatory factors that perform an antimicrobial immune response but partially allow pathogens to replicate and survive intracellularly. Membrane vesicles (MVs) released from bacteria as a distinctive secretion system can carry various components, including bacterial effectors, nucleic acids, or lipids to modulate macrophage polarization in host-pathogen interaction. Similar to MVs, bacteria-infected macrophages can secrete exosomes containing a variety of components to manipulate the phenotypic polarization of "bystander" macrophages nearby or long distance to differentiate into type M1 or M2 to regulate the course of inflammation. Exosomes can also repair tissue damage associated with the infection by upregulating the levels of anti-inflammatory factors, downregulating the pro-inflammatory factors, and regulating cellular biological behaviors. The study of the mechanisms by which EVs modulate macrophage polarization has opened new frontiers in delineating the molecular machinery involved in bacterial pathogenesis and challenges in providing new strategies for diagnosis and therapy.

Engineering probiotic-derived outer membrane vesicles as functional vaccine carriers to enhance immunity against SARS-CoV-2

Because of the continued emergence of SARS-CoV-2 variants, there has been considerable interest in how to display multivalent antigens efficiently. Bacterial outer membrane vesicles (OMVs) can serve as an attractive vaccine delivery system because of their self-adjuvant properties and the ability to be decorated with antigens. Here we set up a bivalent antigen display platform based on engineered OMVs using mCherry and GFP and demonstrated that two different antigens of SARS-CoV-2 could be presented simultaneously in the lumen and on the surface of OMVs. Comparing immunogenicity, ClyA-NG06 fusion and the receptor-binding domain (RBD) of the spike protein in the OMV lumen elicited a stronger humoral response in mice than OMVs presenting either the ClyA-NG06 fusion or RBD alone. Taken together, we provided an efficient approach to display SARS-CoV-2 antigens in the lumen and on the surface of the same OMV and highlighted the potential of OMVs as general multi-antigen carriers.

Membrane Vesicles Derived from Gut Microbiota and Probiotics: Cutting-Edge Therapeutic Approaches for Multidrug-Resistant Superbugs Linked to Neurological Anomalies

Multidrug-resistant (MDR) superbugs can breach the blood-brain barrier (BBB), leading to a continuous barrage of pro-inflammatory modulators and induction of severe infection-related pathologies, including meningitis and brain abscess. Both broad-spectrum or species-specific antibiotics (β-lactamase inhibitors, polymyxins, vancomycin, meropenem, plazomicin, and sarecycline) and biocompatible poly (lactic-co-glycolic acid) (PLGA) nanoparticles have been used to treat these infections. However, new therapeutic platforms with a broad impact that do not exert off-target deleterious effects are needed. Membrane vesicles or extracellular vesicles (EVs) are lipid bilayer-enclosed particles with therapeutic potential owing to their ability to circumvent BBB constraints. Bacteria-derived EVs (bEVs) from gut microbiota are efficient transporters that can penetrate the central nervous system. In fact, bEVs can be remodeled via surface modification and CRISPR/Cas editing and, thus, represent a novel platform for conferring protection against infections breaching the BBB. Here, we discuss the latest scientific research related to gut microbiota- and probiotic-derived bEVs, and their therapeutic modifications, in terms of regulating neurotransmitters and inhibiting quorum sensing, for the treatment of neurodegenerative diseases, such as Parkinson's and Alzheimer's diseases. We also emphasize the benefits of probiotic-derived bEVs to human health and propose a novel direction for the development of innovative heterologous expression systems to combat BBB-crossing pathogens.

Reductions in bacterial viability stimulate the production of Extra-intestinal Pathogenic Escherichia coli (ExPEC) cytoplasm-carrying Extracellular Vesicles (EVs)

Extra-intestinal Pathogenic Escherichia coli (ExPEC) is defined as an extra-intestinal foodborne pathogen, and several dominant sequence types (STs) ExPEC isolates are highly virulent, with zoonotic potential. Bacteria extracellular vesicles (EVs) carry specific subsets of molecular cargo, which affect various biological processes in bacteria and host. The mechanisms of EVs formation in ExPEC remains to be elucidated. Here, the purified EVs of ExPEC strains of different STs were isolated with ultracentrifugation processes. A comparative analysis of the strain proteomes showed that cytoplasmic proteins accounted for a relatively high proportion of the proteins among ExPEC EVs. The proportion of cytoplasm-carrying vesicles in ExPEC EVs was calculated with a simple green fluorescent protein (GFP) expression method. The RecA/LexA-dependent SOS response is a critical mediator of generation of cytoplasm-carrying EVs. The SOS response activates the expression of prophage-associated endolysins, Epel1, Epel2.1, and Epel2.2, which triggered cell lysis, increasing the production of ExPEC cytoplasm-carrying EVs. The repressor LexA controlled directly the expression of these endolysins by binding to the SOS boxes in the endolysin promoter regions. Reducing bacterial viability stimulated the production of ExPEC EVs, especially cytoplasm-carrying EVs. The imbalance in cell division caused by exposure to H₂O₂, the deletion of ftsK genes, or t⁶A synthesis defects activated the RecA/LexA-dependent SOS response, inducing the expression of endolysins, and thus increasing the proportion of cytoplasm-carrying EVs in the total ExPEC EVs. Antibiotics, which decreased bacterial viability, also increase the production of ExPEC cytoplasm-carrying EVs through the SOS response. Changes in the proportion of cytoplasm-carrying EVs affected the total DNA content of ExPEC EVs. When macrophages are exposed to a higher proportion of cytoplasm-carrying vesicles, ExPEC EVs were more cytotoxic to macrophages, accompanied with more-severe mitochondrial disruption and a higher level of induced intrinsic apoptosis. In summary, we offered comprehensive insight into the proteome analysis of ExPEC EVs. This study demonstrated the novel formation mechanisms of E. coli cytoplasm-carrying EVs.

Bacteria can release extracellular vesicles (EVs) into the extracellular environment. Bacterial EVs are primarily composed of protein, DNA, RNA, lipopolysaccharide (LPS), and diverse metabolite molecules. The molecular cargoes of EVs are critical for the interaction between microbes and their hosts, and affected various host biological processes. However, the mechanisms underlying the biogenesis of bacterial EVs had not been fully clarified in extra-intestinal pathogenic Escherichia coli (ExPEC). In this study, we demonstrated ExPEC EVs contained at least three types of vesicles, including outer membrane vesicles (OMVs), outer-inner membrane vesicles (OIMVs), and explosive outer membrane vesicles (EOMVs). Our results systematically identified important factors affecting the production of ExPEC cytoplasm-carrying EVs, especially EOMVs. A reduction in bacterial viability activated the RecA/LexA-dependent SOS response, inducing the expression of endolysins, which increased the production of ExPEC cytoplasm-carrying EVs. This increase in the proportion of cytoplasm-carrying EVs increased the cytotoxicity of EVs. It was noteworthy that antibiotics increased the production of ExPEC EVs, especially the numbers of cytoplasm-carrying EVs, which in turn increased EV cytotoxicity, suggesting that the treatment of infections of multidrug-resistant strains infection with antibiotics might cause greater host damage. Our study should improve the prevention and treatment of ExPEC infections.

Strategies for the Identification and Assessment of Bacterial Strains with Specific Probiotic Traits

Early in the 1900s, it was proposed that health could be improved and senility delayed by manipulating gut microbiota with the host-friendly bacteria found in yogurt. Later, in 1990, the medical community reconsidered this idea and today probiotics represent a developed area of research with a billion-dollar global industry. As a result, in recent decades, increased attention has been paid to the isolation and characterization of novel probiotic bacteria from fermented foods and dairy products. Most of the identified probiotic strains belong to the lactic acid bacteria group and the genus Bifidobacterium. However, current molecular-based knowledge has allowed the identification and culture of obligatory anaerobic commensal bacteria from the human gut, such as Akkermansia spp. and Faecalibacterium spp., among other human symbionts. We are aware that the identification of new strains of these species does not guarantee their probiotic effects and that each effect must be proved through in vitro and in vivo preclinical studies before clinical trials (before even considering it as a probiotic strain). In most cases, the identification and characterization of new probiotic strain candidates may lack the appropriate set of in vitro experiments allowing the next assessment steps. Here, we address some innovative strategies reported in the literature as alternatives to classical characterization: (i) identification of alternatives using whole-metagenome shotgun sequencing, metabolomics, and multi-omics analysis; and (ii) probiotic characterization based on molecular effectors and/or traits to target specific diseases (i.e., inflammatory bowel diseases, colorectal cancer, allergies, among others).

Supplementation of Labneh with Passion Fruit Peel Enhanced Survival of E. coli Nissle 1917 during Simulated Gastrointestinal Digestion and Adhesion to Caco-2 Cells

Passion fruit peel powder (PFPP) was used to supplement the probiotic labneh to increase the activity of Escherichia coli Nissle 1917 (EcN) during production and storage. Labneh was manufactured with PFPP (0.5% and 1%) and analyzed at 0, 7, and 15 days of cold storage for postacidification and sensory properties and viability of EcN, survival of EcN to simulated gastrointestinal tract stress, and adhesion potential of EcN to Caco-2 cells. Acidification kinetics during fermentation showed that supplementation with PFPP reduced the time needed to decrease pH and reach the maximum acidification rate. PFPP addition contributed to postacidification of labneh during storage. PFPP had a beneficial effect (p < 0.05) on counts of EcN in labneh during different storage periods. Consumer preference expectations for labneh enriched with PFPP (0.5% and 1%) were higher than those for the control. PFPP provided a significant protective action for EcN during simulated gastrointestinal transit and had a positive effect on EcN adhesion to Caco-2 cells in vitro, although this decreased during storage with labneh. Labneh supplementation with PFPP can be recommended because of the positive effect on EcN viability and the high nutritional value, which may increase the appeal of the product to consumers.

Probiotics, Their Extracellular Vesicles and Infectious Diseases

Probiotics have been shown to be effective against infectious diseases in clinical trials, with either intestinal or extraintestinal health benefits. Even though probiotic effects are strain-specific, some "widespread effects" include: pathogen inhibition, enhancement of barrier integrity and regulation of immune responses. The mechanisms involved in the health benefits of probiotics are not completely understood, but these effects can be mediated, at least in part, by probiotic-derived extracellular vesicles (EVs). However, to date, there are no clinical trials examining probiotic-derived EVs health benefits against infectious diseases. There is still a long way to go to bridge the gap between basic research and clinical practice. This review attempts to summarize the current knowledge about EVs released by probiotic bacteria to understand their possible role in the prevention and/or treatment of infectious diseases. A better understanding of the mechanisms whereby EVs package their cargo and the process involved in communication with host cells (inter-kingdom communication), would allow further advances in this field. In addition, we comment on the potential use and missing knowledge of EVs as therapeutic agents (postbiotics) against infectious diseases. Future research on probiotic-derived EVs is needed to open new avenues for the encapsulation of bioactives inside EVs from GRAS (Generally Regarded as Safe) bacteria. This could be a scientific novelty with applications in functional foods and pharmaceutical industries.

The Outer Membrane Vesicles of Salmonella enterica Serovar Typhimurium Activate Chicken Immune Cells through Lipopolysaccharides and Membrane Proteins

Salmonella is a common pathogen which can secrete outer membrane vesicles (OMVs). However, the effect of OMVs from Salmonella enterica Serovar Typhimurium (S. Typhimurium) of poultry origin on cells of the chicken innate immune system is not well known. In this study, S. Typhimurium OMVs were first isolated from three different poultry strains of Salmonella, Salmonella CVCC542, SALA, and SALB. In order to investigate the effect of OMVs on the maturation of monocytes into macrophages, both bone marrow-derived (BMD) monocytes and macrophage cell line HD11 cells were used. OMVs promoted the formation of monocyte dendrites in both types of cells, enabled BMD cells to become larger, and stimulated expression of LPS-induced TNF-αfactor (LITAF), IL-6, and inducible nitric oxide synthase (iNOS) genes in HD11 cells. These results demonstrated the capability of OMVs to promote the development of chicken monocytes into macrophages and the maturation of macrophages. In order to study the effect of OMVs on the phagocytosis of macrophages, chicken spleen-derived monocytes and HD11 cells were used. Phagocytosis of FITC-Salmonella and FITC-dextran by these two types of cells was enhanced after stimulation with OMVs. To determine which components in OMVs were responsible for the above observed results, OMVs were treated with proteinase K(PK) or polymyxin B (PMB). Both treatments reduced the phagocytosis of FITC-Salmonella by HD11 cells and chicken spleen mononuclear cells and reduced the secretion of IL-1β, LITAF, and IL-6 cytokines. These results demonstrated that Salmonella OMVs activated chicken macrophages and spleen mononuclear cells and the activation was achieved mainly through lipopolysaccharides and membrane proteins.

Native and Engineered Probiotics: Promising Agents against Related Systemic and Intestinal Diseases

Intestinal homeostasis is a dynamic balance involving the interaction between the host intestinal mucosa, immune barrier, intestinal microecology, nutrients, and metabolites. Once homeostasis is out of balance, it will increase the risk of intestinal diseases and is also closely associated with some systemic diseases. Probiotics (Escherichia coli Nissle 1917, Akkermansia muciniphila, Clostridium butyricum, lactic acid bacteria and Bifidobacterium spp.), maintaining the gut homeostasis through direct interaction with the intestine, can also exist as a specific agent to prevent, alleviate, or cure intestinal-related diseases. With genetic engineering technology advancing, probiotics can also show targeted therapeutic properties. The aims of this review are to summarize the roles of potential native and engineered probiotics in oncology, inflammatory bowel disease, and obesity, discussing the therapeutic applications of these probiotics.

The seven constitutive respiratory defense barriers against SARS-CoV-2 infection

Before eliciting an adaptive immune response, SARS-CoV-2 must overcome seven constitutive respiratory defense barriers. The first is the mucus covering the respiratory tract's luminal surface, which entraps inhaled particles, including infectious agents, and eliminates them by mucociliary clearance. The second barrier comprises various components present in the airway lining fluid, the surfactants. Besides providing low surface tension that allows efficient gas exchange at the alveoli, surfactants inhibit the invasion of epithelial cells by respiratory viruses, enhance pathogen uptake by phagocytes, and regulate immune cells' functions. The respiratory tract microbiota constitutes the third defense barrier against SARS-CoV-2. It activates the innate and adaptive immune cells and elicits anti-infectious molecules such as secretory IgA antibodies, defensins, and interferons. The fourth defense barrier comprises the antimicrobial peptides defensins, and lactoferrin. They show direct antiviral activity, inhibit viral fusion, and modulate the innate and adaptive immune responses. Secretory IgA antibodies, the fifth defense barrier, besides protecting the local microbiota against noxious agents, also inhibit SARS-CoV-2 cell invasion. If the virus overcomes this barrier, it reaches its target, the respiratory epithelial cells. However, these cells also act as a defense barrier, the sixth one, since they hinder the virus' access to receptors and produce antiviral and immunomodulatory molecules such as interferons, lactoferrin, and defensins. Finally, the sensing of the virus by the cells of innate immunity, the last constitutive defense barrier, elicits a cascade of signals that activate adaptive immune cells and may inhibit the development of productive infection. The subject of the present essay is discussing these mechanisms.

Francisella tularensis Outer Membrane Vesicles Participate in the Early Phase of Interaction With Macrophages

Francisella tularensis is known to release unusually shaped tubular outer membrane vesicles (OMV) containing a number of previously identified virulence factors and immunomodulatory proteins. In this study, we present that OMV isolated from the F. tularensis subsp. holarctica strain FSC200 enter readily into primary bone marrow-derived macrophages (BMDM) and seem to reside in structures resembling late endosomes in the later intervals. The isolated OMV enter BMDM generally via macropinocytosis and clathrin-dependent endocytosis, with a minor role played by lipid raft-dependent endocytosis. OMVs proved to be non-toxic and had no negative impact on the viability of BMDM. Unlike the parent bacterium itself, isolated OMV induced massive and dose-dependent proinflammatory responses in BMDM. Using transmission electron microscopy, we also evaluated OMV release from the bacterial surface during several stages of the interaction of Francisella with BMDM. During adherence and the early phase of the uptake of bacteria, we observed numerous tubular OMV-like protrusions bulging from the bacteria in close proximity to the macrophage plasma membrane. This suggests a possible role of OMV in the entry of bacteria into host cells. On the contrary, the OMV release from the bacterial surface during its cytosolic phase was negligible. We propose that OMV play some role in the extracellular phase of the interaction of Francisella with the host and that they are involved in the entry mechanism of the bacteria into macrophages.

Bacterial extracellular vesicles: Understanding biology promotes applications as nanopharmaceuticals

Extracellular vesicle (EV)-mediated communication between proximal and distant cells is a highly conserved characteristic in all of the life domains, including bacteria. These vesicles that contain a variety of biomolecules, such as proteins, lipids, nucleic acids, and small-molecule metabolites play a key role in the biology of bacteria. They are one of the key underlying mechanisms behind harmful or beneficial effects of many pathogenic, symbiont, and probiotic bacteria. These nanoscale EVs mediate extensive crosstalk with mammalian cells and deliver their cargos to the host. They are stable in physiological condition, can encapsulate diverse biomolecules and nanoparticles, and their surface could be engineered with available technologies. Based on favorable characteristics of bacterial vesicles, they can be harnessed for designing a diverse range of therapeutics and diagnostics for treatment of disorders including tumors and resistant infections. However, technical limitations for their production, purification, and characterization must be addressed in future studies.

The impact of ExHp-CD (outer membrane vesicles) released from Helicobacter pylori SS1 on macrophage RAW 264.7 cells and their immunogenic potential

Bacterial-derived extracellular vesicles could play a major role in attenuating and treating diseases. They play a major anti-infection role by modulating immune responses against pathogens and preventing infection by inhibiting pathogen localization and proliferation. In this study, outer membrane vesicles (ExHp-CD) released by Helicobacter pylori SS1 (H. pylori) and total antigens isolated from H. pylori SS1 (AgHp) were evaluated for their immunogenic potential and their effect on macrophage RAW 264.7 cells. Results demonstrated that both ExHp-CD and AgHp induced T helper 2 (Th2) immune response, which was reported to be important in immune protection against H. pylori infections. Both ExHp-CD and AgHp produced high levels of IL-10 and IL-4, while no significant levels of IL-12 p70 or IFN-γ were detected. However, ExHp-CD showed a better effect on macrophage RAW 264.7 cells compared to AgHp. Macrophage RAW 264.7 cells stimulated with 5, and 10 μg/mL of ExHp-CD showed an increased ratio of CD206 (M2 phenotype marker) and a decreased ratio of CD86 (M1 phenotype marker). Moreover, results suggested that the immunogenic effect that ExHp-CD possesses was attributed to their cargo of Epimerase_2 domain-containing protein (Epi_2D), Probable malate:quinone oxidoreductase (Pro_mqo), and Probable cytosol aminopeptidase (Pro_ca). Results demonstrated that ExHp-CD possesses an immunological activity to induce Th2 immune response against H. pylori infection with results comparable to AgHp. However, ExHp-CD showed higher efficacy regarding safety, biocompatibility, lack of toxicity, and hemocompatibility. Thus, it could serve as an immunogenic candidate with more desired characteristics.