Vesiculation from Pseudomonas aeruginosa under SOS

In Vitro/Vivo Mechanisms of Antibacterial Peptide NZ2114 against Staphylococcus pseudintermedius and Its Biofilms

Staphylococcus pseudintermedius is an opportunistic pathogen commonly found in canines, and has garnered escalating interest due to its potential for zoonotic transmission and increasing antimicrobial resistance. However, the excessive use of antibiotics and the characteristic of S. pseudintermedius forming biofilms make treatment challenging. In this study, the in vivo and in vitro antimicrobial activity and mechanisms of action of NZ2114, a plectasin-derived peptide, against S. pseudintermedius were investigated. NZ2114 exhibited potent antibacterial activity towards S. pseudintermedius (minimum inhibitory concentration, MIC = 0.23 μM) with a lower probability of inducing drug-resistant mutations and efficient bactericidal action, which was superior to those of mopirucin (MIC = 0.25-0.5 μM) and lincomycin (MIC = 4.34-69.41 μM). The results of electron microscopy and flow cytometry showed that NZ2114 disrupted S. pseudintermedius' cell membrane, resulting in cellular content leakage, cytoplasmic membrane shrinkage, and, eventually, cell death. The intracellular ROS activity and Alamar Blue detection showed that NZ2114 interferes with intracellular metabolic processes. In addition, NZ2114 effectively inhibits biofilm formation, and confocal laser scanning microscopy further revealed its antibacterial and anti-biofilm activity (biofilm thickness reduced to 6.90-17.70 μm). The in vivo therapy of NZ2114 in a mouse pyoderma model showed that it was better than lincomycin in effectively decreasing the number of skin bacteria, alleviating histological damage, and reducing the skin damage area. These results demonstrated that NZ2114 may be a promising antibacterial candidate against S. pseudintermedius infections.

Exploiting phage-antibiotic synergies to disrupt Pseudomonas aeruginosa PAO1 biofilms in the context of orthopedic infections

IMPORTANCE

Biofilm-related infections are among the most difficult-to-treat infections in all fields of medicine due to their antibiotic tolerance and persistent character. In the field of orthopedics, these biofilms often lead to therapeutic failure of medical implantable devices and urgently need novel treatment strategies. This forthcoming article aims to explore the dynamic interplay between newly isolated bacteriophages and routinely used antibiotics and clearly indicates synergetic patterns when used as a dual treatment modality. Biofilms were drastically more reduced when both active agents were combined, thereby providing additional evidence that phage-antibiotic combinations lead to synergism and could potentially improve clinical outcome for affected patients.

OprF functions as a latch to direct Outer Membrane Vesicle release in Pseudomonas aeruginosa

Bacterial Outer Membrane Vesicles (OMVs) contribute to virulence, competition, immune avoidance and communication. This has led to great interest in how they are formed. To date, investigation has focused almost exclusively on what controls the initiation of OMV biogenesis. Regardless of the mechanism of initiation, all species face a similar challenge before an OMV can be released: How does the OM detach from the underlying peptidoglycan (PG) in regions that will ultimately bulge and then vesiculate? The OmpA family of OM proteins (OprF in P. aeruginosa) is widely conserved and unusually abundant in OMVs across species considering their major role in PG attachment. OmpA homologs also have the interesting ability to adopt both PG-bound (two-domain) and PG-released (one-domain) conformations. Using targeted deletion of the PG-binding domain we showed that loss of cell wall association, and not general membrane destabilization, is responsible for hypervesiculation in OprF-modified strains. We therefore propose that OprF functions as a 'latch', capable of releasing PG in regions destined to become OMVs. To test this hypothesis, we developed a protocol to assess OprF conformation in live cells and purified OMVs. While >90% of OprF proteins exist in the two-domain conformation in the OM of cells, we show that the majority of OprF in OMVs is present in the one-domain conformation. With this work, we take some of the first steps in characterizing late-stage OMV biogenesis and identify a family of proteins whose critical role can be explained by their unique ability to fold into two distinct conformations.

Peptide MSI-1 inhibited MCR-1 and regulated outer membrane vesicles to combat immune evasion of Escherichia coli

Polymyxin resistance is conferred by MCR-1 (mobile colistin resistance 1)-induced lipopolysaccharide (LPS) modification of G- bacteria. However, the peptide MSI-1 exerts potent antimicrobial activity against mcr-1-carrying bacteria. To further investigate the potential role of MCR-1 in improving bacterial virulence and facilitating immune evasion, and the immunomodulatory effect of peptide MSI-1, we first explored outer membrane vesicle (OMV) alterations of mcr-1-carrying bacteria in the presence and absence of sub-MIC MSI-1, and host immune activation during bacterial infection and OMV stimulation. Our results demonstrated that LPS remodelling induced by MCR-1 negatively affected OMV formation and protein cargo by E. coli. In addition, MCR-1 diminished LPS-stimulated pyroptosis but facilitated mitochondrial dysfunction, further aggravating apoptosis in macrophages induced by OMVs of E. coli. Similarly, TLR4-mediated NF-κB activation was markedly alleviated once LPS was modified by MCR-1. However, peptide MSI-1 at the sub-MIC level inhibited the expression of MCR-1, further partly rescuing OMV alteration and attenuation of immune responses in the presence of MCR-1 during both infection and OMV stimulation, which can be exploited for anti-infective therapy.

Plasmid-mediated virulence in Chlamydia

Chlamydia trachomatis infection of ocular conjunctiva can lead to blindness, while infection of the female genital tract can lead to chronic pelvic pain, ectopic pregnancy, and/or infertility. Conjunctival and fallopian tube inflammation and the resulting disease sequelae are attributed to immune responses induced by chlamydial infection at these mucosal sites. The conserved chlamydial plasmid has been implicated in enhancing infection, via improved host cell entry and exit, and accelerating innate inflammatory responses that lead to tissue damage. The chlamydial plasmid encodes eight open reading frames, three of which have been associated with virulence: a secreted protein, Pgp3, and putative transcriptional regulators, Pgp4 and Pgp5. Although Pgp3 is an important plasmid-encoded virulence factor, recent studies suggest that chlamydial plasmid-mediated virulence extends beyond the expression of Pgp3. In this review, we discuss studies of genital, ocular, and gastrointestinal infection with C. trachomatis or C. muridarum that shed light on the role of the plasmid in disease development, and the potential for tissue and species-specific differences in plasmid-mediated pathogenesis. We also review evidence that plasmid-associated inflammation can be independent of bacterial burden. The functions of each of the plasmid-encoded proteins and potential molecular mechanisms for their role(s) in chlamydial virulence are discussed. Although the understanding of plasmid-associated virulence has expanded within the last decade, many questions related to how and to what extent the plasmid influences chlamydial infectivity and inflammation remain unknown, particularly with respect to human infections. Elucidating the answers to these questions could improve our understanding of how chlamydia augment infection and inflammation to cause disease.

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.

Correlation between bacterial extracellular vesicles and antibiotics: A potentially antibacterial strategy

Bacterial extracellular vesicles (BEVs) are proteoliposome nanoparticles that are secreted by both Gram-negative (G^-) and Gram-positive (G⁺) bacteria. BEVs have significant roles in various physiological processes of bacteria, including driving inflammatory responses, regulating bacterial pathogenesis, and promoting bacterial survival in diverse environments. Recently, there has been increasing interest in the use of BEVs as a potential solution to antibiotic resistance. BEVs have shown great promise as a new approach to antibiotics, as well as a drug-delivery tool in antimicrobial strategies. In this review, we provide a summary of recent scientific advances in BEVs and antibiotics, including BEV biogenesis, ability to kill bacteria, potential for delivering antibiotics, and their role in the development of vaccines or as immune adjuvants. We propose that BEVs provide a novel antimicrobial strategy that would be beneficial against the increasing threat of antibiotic resistance.

Exosomes: from biology to immunotherapy in infectious diseases

Exosomes are extracellular vesicles derived from the endosomal compartment, which are released by all kinds of eukaryotic and prokaryotic organisms. These vesicles contain a variety of biomolecules that differ both in quantity and type depending on the origin and cellular state. Exosomes are internalized by recipient cells, delivering their content and thus contributing to cell-cell communication in health and disease. During infections exosomes may exert a dual role, on one hand, they can transmit pathogen-related molecules mediating further infection and damage, and on the other hand, they can protect the host by activating the immune response and reducing pathogen spread. Selective packaging of pathogenic components may mediate these effects. Recently, quantitative analysis of samples by omics technologies has allowed a deep characterization of the proteins, lipids, RNA, and metabolite cargoes of exosomes. Knowledge about the content of these vesicles may facilitate their therapeutic application. Furthermore, as exosomes have been detected in almost all biological fluids, pathogenic or host-derived components can be identified in liquid biopsies, making them suitable for diagnosis and prognosis. This review attempts to organize the recent findings on exosome composition and function during viral, bacterial, fungal, and protozoan infections, and their contribution to host defense or to pathogen spread. Moreover, we summarize the current perspectives and future directions regarding the potential application of exosomes for prophylactic and therapeutic purposes.

The role of bacterial membrane vesicles in antibiotic resistance

Bacterial survival during antibiotic exposure is a complex and multifaceted phenomenon. On top of antibiotic resistance genes, biofilm formation, and persister tolerance, bacterial membrane vesicles (MVs) provide a layer of protection that has been largely overlooked. MVs are spherical nanoparticles composed of lipid membranes and are common to Gram-positive and Gram-negative bacteria. Although the importance of MVs in bacterial pathogenesis and virulence factor transport has been firmly established, a growing body of work now identifies MVs as key contributors to bacterial survival during antibiotic exposure. Herein, we highlight the ability of MVs to reduce antibiotic efficacy and transmit resistance elements. We also discuss the potential of targeting MV production as an unconventional therapeutic approach.

Production and purification of bacterial membrane vesicles for biotechnology applications: Challenges and opportunities

Bacterial membrane vesicles (BMVs) are bi-layered nanostructures derived from Gram-negative and Gram-positive bacteria. Among other pathophysiological roles, BMVs are critical messengers in intercellular communication. As a result, BMVs are emerging as a promising technology for the development of numerous therapeutic applications. Despite the remarkable progress in unveiling BMV biology and functions in recent years, their successful isolation and purification have been limited. Several challenges related to vesicle purity, yield, and scalability severely hamper the further development of BMVs for biotechnology and clinical applications. This review focuses on the current technologies and methodologies used in BMV production and purification, such as ultracentrifugation, density-gradient centrifugation, size-exclusion chromatography, ultrafiltration, and precipitation. We also discuss the current challenges related to BMV isolation, large-scale production, storage, and stability that limit their application. More importantly, the present work explains the most recent strategies proposed for overcoming those challenges. Finally, we summarize the ongoing applications of BMVs in the biotechnological field.

Spontaneous Prophage Induction Contributes to the Production of Membrane Vesicles by the Gram-Positive Bacterium Lacticaseibacillus casei BL23

The formation of membrane vesicles (MVs) by Gram-positive bacteria has gained increasing attention over the last decade. Recently, models of vesicle formation have been proposed and involve the digestion of the cell wall by prophage-encoded or stress-induced peptidoglycan (PG) hydrolases and the inhibition of PG synthesis by β-lactam antibiotics. The impact of these mechanisms on vesicle formation is largely dependent on the strain and growth conditions. To date, no information on the production of vesicles by the lactobacilli family has been reported. Here, we aimed to characterize the MVs released by the Gram-positive bacteria Lacticaseibacillus casei BL23 and also investigated the mechanisms involved in vesicle formation. Using electron microscopy, we established that the size of the majority of L. casei BL23 vesicles ranged from 50 to 100 nm. Furthermore, we showed that the vesicles were released consistently throughout the growth of the bacteria in standard culture conditions. The protein composition of the vesicles released in the supernatant was identified and a significant number of prophage proteins was detected. Moreover, using a mutant strain harboring a defective PLE2 prophage, we were able to show that the spontaneous and mitomycin-triggered induction of the prophage PLE2 contribute to the production of MVs by L. casei BL23. Finally, we also demonstrated the influence of prophages on the membrane integrity of bacteria. Overall, our results suggest a key role of the prophage PLE2 in the production of MVs by L. casei BL23 in the absence or presence of genotoxic stress.

Research Progress on Bacterial Membrane Vesicles and Antibiotic Resistance

As a result of antibiotic overuse, bacterial antibiotic resistance has become a severe threat to worldwide public health. The development of more effective antimicrobial therapies and alternative antibiotic strategies is urgently required. The role played by bacterial membrane vesicles (BMVs) in antibiotic resistance has become a current focus of research. BMVs are nanoparticles derived from the membrane components of Gram-negative and Gram-positive bacteria and contain diverse components originating from the cell envelope and cytoplasm. Antibiotic stress stimulates the secretion of BMVs. BMVs promote and mediate antibiotic resistance by multiple mechanisms. BMVs have been investigated as conceptually new antibiotics and drug-delivery vehicles. In this article, we outline the research related to BMVs and antibiotic resistance as a reference for the intentional use of BMVs to combat antibiotic resistance.

Outer Membrane Vesicles as Molecular Biomarkers for Gram-negative Sepsis: Taking Advantage of Nature's Perfect Packages

Sepsis is an often life-threatening response to infection, occurring when host pro-inflammatory immune responses become abnormally elevated and dysregulated. To diagnose sepsis, the patient must have a confirmed or predicted infection, as well as other symptoms associated with the pathophysiology of sepsis. However, a recent study found that a specific causal organism could not be determined in the majority (70.1%) of sepsis cases, likely due to aggressive antibiotics or localized infections. The timing of a patient's sepsis diagnosis is often predictive of their clinical outcome, underlining the need for a more definitive molecular diagnostic test. Here, we outline the advantages and challenges to using bacterial outer membrane vesicles (OMVs), nanoscale spherical buds derived from the outer membrane of Gram-negative bacteria, as a diagnostic biomarker for Gram-negative sepsis. Advantages include OMV abundance, their robustness in the presence of antibiotics, and their unique features derived from their parent cell that could allow for differentiation between bacterial species. Challenges include the rigorous purification methods required to isolate OMVs from complex biofluids and the additional need to separate OMVs from similarly-sized extracellular vesicles, which can share physical properties with OMVs.

Airway acidification impaired host defense against Pseudomonas aeruginosa infection by promoting type 1 interferon β response

Airway microenvironment played an important role in the progression of chronic respiratory disease. Here we showed that standardized pondus hydrogenii (pH) of exhaled breath condensate (EBC) of bronchiectasis patients was significantly lower than that of controls and was significantly correlated with bronchiectasis severity index (BSI) scores and disease prognosis. EBC pH was lower in severe patients than that in mild and moderate patients. Besides, acidic microenvironment deteriorated Pseudomonas aeruginosa (P. aeruginosa) pulmonary infection in mice models. Mechanistically, acidic microenvironment increased P. aeruginosa outer membrane vesicles (PA_OMVs) released and boosted it induced the activation of interferon regulatory factor3 (IRF3)-interferonβ (IFN-β) signalling pathway, ultimately compromised the anti-bacteria immunity. Targeted knockout of IRF3 or type 1 interferon receptor (IFNAR1) alleviated lung damage and lethality of mice after P. aeruginosa infection that aggravated by acidic microenvironment. Together, these findings identified airway acidification impaired host resistance to P. aeruginosa infection by enhancing it induced the activation of IRF3-IFN-β signalling pathway. Standardized EBC pH may be a useful biomarker of disease severity and a potential therapeutic target for the refractory P. aeruginosa infection. The study also provided one more reference parameter for drug selection and new drug discovery for bronchiectasis.

Engineered bacterial membrane vesicles are promising carriers for vaccine design and tumor immunotherapy

Bacterial membrane vesicles (BMVs) have emerged as novel and promising platforms for the development of vaccines and immunotherapeutic strategies against infectious and noninfectious diseases. The rich microbe-associated molecular patterns (MAMPs) and nanoscale membrane vesicle structure of BMVs make them highly immunogenic. In addition, BMVs can be endowed with more functions via genetic and chemical modifications. This article reviews the immunological characteristics and effects of BMVs, techniques for BMV production and modification, and the applications of BMVs as vaccines or vaccine carriers. In summary, given their versatile characteristics and immunomodulatory properties, BMVs can be used for clinical vaccine or immunotherapy applications.

The Q225P Mutation in SigB Promotes Membrane Vesicle Formation in Staphylococcus aureus

Both Gram-positive and Gram-negative bacteria release nano-sized lipid bilayered particles, known as membrane vesicles (MVs), into external environments. Although MVs play a variety of roles in bacterial physiology and pathogenesis, the mechanisms underlying MV formation in Gram-positive microorganisms such as Staphylococcus aureus remain obscure. Bacterial MV production can be induced in response to stress conditions, and the alternative sigma factor B (SigB) functions as a central regulator of the stress response in Gram-positive bacteria. In a previous study, we demonstrated that the SigB(Q225P) substitution mutation in S. aureus promotes biofilm formation. Here, we report that the SigB(Q225P) mutation also increases MV production in this important pathogen. LacZ reporter assays and electrophoretic mobility shift assays showed that the Q225P substitution reduces SigB binding to the promoter region of the thermonuclease gene (nuc), resulting in a significant reduction in Nuc expression. Deletion of nuc markedly enhances S. aureus MV generation, possibly due to the accumulation of nucleic acids. These results are not only important for understanding MV biogenesis in S. aureus, but also useful for the development of a S. aureus MV-based platform for MV application.

The Extracellular Vesicles from the Commensal Staphylococcus Epidermidis ATCC12228 Strain Regulate Skin Inflammation in the Imiquimod-Induced Psoriasis Murine Model

Extracellular vesicles (EVs) are evaginations of the cytoplasmic membrane, containing nucleic acids, proteins, lipids, enzymes, and toxins. EVs participate in various bacterial physiological processes. Staphylococcus epidermidis interacts and communicates with the host skin. S. epidermidis’ EVs may have an essential role in this communication mechanism, modulating the immunological environment. This work aimed to evaluate if S. epidermidis’ EVs can modulate cytokine production by keratinocytes in vitro and in vivo using the imiquimod-induced psoriasis murine model. S. epidermidis’ EVs were obtained from a commensal strain (ATC12228EVs) and a clinical isolated strain (983EVs). EVs from both origins induced IL-6 expression in HaCaT keratinocyte cultures; nevertheless, 983EVs promoted a higher expression of the pro-inflammatory cytokines VEGF-A, LL37, IL-8, and IL-17F than ATCC12228EVs. Moreover, in vivo imiquimod-induced psoriatic skin treated with ATCC12228EVs reduced the characteristic psoriatic skin features, such as acanthosis and cellular infiltrate, as well as VEGF-A, IL-6, KC, IL-23, IL-17F, IL-36γ, and IL-36R expression in a more efficient manner than 983EVs; however, in contrast, Foxp3 expression did not significantly change, and IL-36 receptor antagonist (IL-36Ra) was found to be increased. Our findings showed a distinctive immunological profile induction that is dependent on the clinical or commensal EV origin in a mice model of skin-like psoriasis. Characteristically, proteomics analysis showed differences in the EVs protein content, dependent on origin of the isolated EVs. Specifically, in ATCC12228EVs, we found the proteins glutamate dehydrogenase, ornithine carbamoyltransferase, arginine deiminase, carbamate kinase, catalase, superoxide dismutase, phenol-soluble β1/β2 modulin, and polyglycerol phosphate α-glucosyltransferase, which could be involved in the reduction of lesions in the murine imiquimod-induced psoriasis skin. Our results show that the commensal ATCC12228EVs have a greater protective/attenuating effect on the murine imiquimod-induced psoriasis by inducing IL-36Ra expression in comparison with EVs from a clinical isolate of S. epidermidis.

The extracellular vesicle generation paradox: a bacterial point of view

All bacteria produce secreted vesicles that carry out a variety of important biological functions. These extracellular vesicles can improve adaptation and survival by relieving bacterial stress and eliminating toxic compounds, as well as by facilitating membrane remodeling and ameliorating inhospitable environments. However, vesicle production comes with a price. It is energetically costly and, in the case of colonizing pathogens, it elicits host immune responses, which reduce bacterial viability. This raises an interesting paradox regarding why bacteria produce vesicles and begs the question as to whether the benefits of producing vesicles outweigh their costs. In this review, we discuss the various advantages and disadvantages associated with Gram-negative and Gram-positive bacterial vesicle production and offer perspective on the ultimate score. We also highlight questions needed to advance the field in determining the role for vesicles in bacterial survival, interkingdom communication, and virulence.

Potential Applications of Microparticulate-Based Bacterial Outer Membrane Vesicles (OMVs) Vaccine Platform for Sexually Transmitted Diseases (STDs): Gonorrhea, Chlamydia, and Syphilis

Sexually transmitted diseases (STDs) are a major global health issue. Approximately 250 million new cases of STDs occur each year globally. Currently, only three STDs (human papillomavirus (HPV), hepatitis A, and hepatitis B) are preventable by vaccines. Vaccines for other STDs, including gonorrhea, chlamydia, and syphilis, await successful development. Currently, all of these STDs are treated with antibiotics. However, the efficacy of antibiotics is facing growing challenge due to the emergence of bacterial resistance. Therefore, alternative therapeutic approaches, including the development of vaccines against these STDs, should be explored to tackle this important global public health issue. Mass vaccination could be more efficient in reducing the spread of these highly contagious diseases. Bacterial outer membrane vesicle (OMV) is a potential antigen used to prevent STDs. OMVs are released spontaneously during growth by many Gram-negative bacteria. They present a wide range of surface antigens in native conformation that possess interesting properties such as immunogenicity, adjuvant potential, and the ability to be taken up by immune cells, all of which make them an attractive target for application as vaccines against pathogenic bacteria. The major challenge associated with the use of OMVs is its fragile structure and stability. However, a particulate form of the vaccine could be a suitable delivery system that can protect the antigen from degradation by a harsh acidic or enzymatic environment. The particulate form of the vaccine can also act as an adjuvant by itself. This review will highlight some practical methods for formulating microparticulate OMV-based vaccines for STDs.

Engineered Remolding and Application of Bacterial Membrane Vesicles

Bacterial membrane vesicles (MVs) are produced by both Gram-positive and Gram-negative bacteria during growth in vitro and in vivo. MVs are nanoscale vesicular structures with diameters ranging from 20 to 400 nm. MVs incorporate bacterial lipids, proteins, and often nucleic acids, and can effectively stimulate host immune response against bacterial infections. As vaccine candidates and drug delivery systems, MVs possess high biosafety owing to the lack of self-replication ability. However, wild-type bacterial strains have poor MV yield, and MVs from the wild-type strains may be harmful due to the carriage of toxic components, such as lipopolysaccharides, hemolysins, enzymes, etc. In this review, we summarize the genetic modification of vesicle-producing bacteria to reduce MV toxicity, enhance vesicle immunogenicity, and increase vesicle production. The engineered MVs exhibit broad applications in vaccine designs, vaccine delivery vesicles, and drug delivery systems.

In Vivo Secretion of β-Lactamase-Carrying Outer Membrane Vesicles as a Mechanism of β-Lactam Therapy Failure

Outer membrane vesicles carrying β-lactamase (βLOMVs) protect bacteria against β-lactam antibiotics under experimental conditions, but their protective role during a patient’s treatment leading to the therapy failure is unknown. We investigated the role of βLOMVs in amoxicillin therapy failure in a patient with group A Streptococcus pyogenes (GAS) pharyngotonsillitis. The patient’s throat culture was examined by standard microbiological procedures. Bacterial vesicles were analyzed for β-lactamase by immunoblot and the nitrocefin assay, and in vivo secretion of βLOMVs was detected by electron microscopy. These analyses demonstrated that the patient’s throat culture grew, besides amoxicillin-susceptible GAS, an amoxicillin-resistant nontypeable Haemophilus influenzae (NTHi), which secreted βLOMVs. Secretion and β-lactamase activity of NTHi βLOMVs were induced by amoxicillin concentrations reached in the tonsils during therapy. The presence of NTHi βLOMVs significantly increased the minimal inhibitory concentration of amoxicillin for GAS and thereby protected GAS against bactericidal concentrations of amoxicillin. NTHi βLOMVs were identified in the patient’s pharyngotonsillar swabs and saliva, demonstrating their secretion in vivo at the site of infection. We conclude that the pathogen protection via βLOMVs secreted by the flora colonizing the infection site represents a yet underestimated mechanism of β-lactam therapy failure that warrants attention in clinical studies.

Helicobacter pylori-derived outer membrane vesicles stimulate interleukin 8 secretion through nuclear factor kappa B activation

BACKGROUND/AIMS

Bacteria-derived outer membrane vesicles (OMVs) are commonly associated with various biological activities and functions. Helicobacter pylori-derived OMVs are thought to contribute to pathogenesis. This study aimed to investigate the effects of H. pylori-derived OMVs.

METHODS

H. pylori strains were isolated from patients with gastritis, gastric ulcer, or gastric cancer using endoscopic biopsy. The U-937, AGS, and MKN-45 cell lines were exposed to H. pylori and H. pylori-derived OMVs. The expression of interleukin 8 (IL-8) messenger RNA (mRNA) was assessed using reverse transcription-polymerase chain reaction (RT-PCR) and real-time RT-PCR, and IL-8 secretion was analyzed using enzyme-linked immunosorbent assay. Nuclear factor kappa B (NF-κB) activation was evaluated by Western blotting.

RESULTS

H. pylori and H. pylori-derived OMVs induced the expression of IL-8 mRNA and protein. Importantly, the bacteria induced higher IL-8 mRNA and protein expression than the OMVs. IL-8 expression was induced to different levels in response to H. pylori-derived OMVs from hosts with different gastric diseases. Western blotting revealed the increased phosphorylation and reduced degradation of inhibitor of NF-κB alpha in cells exposed to OMVs.

CONCLUSION

H. pylori-derived OMVs may aid the development of various gastric diseases by inducing IL-8 production and NF-κB activation.

Extracellular Vesicles and Host-Pathogen Interactions: A Review of Inter-Kingdom Signaling by Small Noncoding RNA

The focus of this brief review is to describe the role of noncoding regulatory RNAs, including short RNAs (sRNA), transfer RNA (tRNA) fragments and microRNAs (miRNA) secreted in extracellular vesicles (EVs), in inter-kingdom communication between bacteria and mammalian (human) host cells. Bacteria secrete vesicles that contain noncoding regulatory RNAs, and recent studies have shown that the bacterial vesicles fuse with and deliver regulatory RNAs to host cells, and similar to eukaryotic miRNAs, regulatory RNAs modulate the host immune response to infection. Recent studies have also demonstrated that mammalian cells secrete EVs containing miRNAs that regulate the gut microbiome, biofilm formation and the bacterial response to antibiotics. Thus, as evidence accumulates it is becoming clear that the secretion of noncoding regulatory RNAs and miRNAs in extracellular vesicles is an important mechanism of bidirectional communication between bacteria and mammalian (human) host cells. However, additional research is necessary to elucidate how noncoding regulatory RNAs and miRNA secreted in extracellular vesicles mediate inter-kingdom communication.

Fight bacteria with bacteria: Bacterial membrane vesicles as vaccines and delivery nanocarriers against bacterial infections

Bacterial membrane vesicles (MVs) are particles secreted by bacteria with diameter of 20-400 nm. The pathogen-associated molecular patterns (PAMPs) present on the surface of MVs are capable of activating human immune system, leading to non-specific immune response and specific immune response. Due to the immunostimulatory properties and proteoliposome nanostructures, MVs have been increasingly explored as vaccines or delivery systems for the prevention and treatment of bacterial infections. Herein, the recent progresses of MVs for antibacterial applications are reviewed to provide an overview of MVs vaccines and MVs-related delivery systems. In addition, the safety issues of bacterial MVs are discussed to demonstrate their potential for clinical translation. In the end of this review, the challenges of bacterial MVs as vaccines and delivery systems for clinical applications are highlighted with the purpose of predicting future research directions in this field.

Outer Membrane Vesicles (OMVs) Produced by Gram-Negative Bacteria: Structure, Functions, Biogenesis, and Vaccine Application

Gram-negative bacteria produce outer membrane vesicles (OMVs) with 10 to 300 nm of diameter. The contribution of OMVs to bacterial pathogenesis is a topic of great interest, and their capacity to be combined with antigens impact in the future to the development of vaccines.

Eco-evolutionary feedbacks mediated by bacterial membrane vesicles

Bacterial membrane vesicles (BMVs) are spherical extracellular organelles whose cargo is enclosed by a biological membrane. The cargo can be delivered to distant parts of a given habitat in a protected and concentrated manner. This review presents current knowledge about BMVs in the context of bacterial eco-evolutionary dynamics among different environments and hosts. BMVs may play an important role in establishing and stabilizing bacterial communities in such environments; for example, bacterial populations may benefit from BMVs to delay the negative effect of certain evolutionary trade-offs that can result in deleterious phenotypes. BMVs can also perform ecosystem engineering by serving as detergents, mediators in biochemical cycles, components of different biofilms, substrates for cross-feeding, defense systems against different dangers and enzyme-delivery mechanisms that can change substrate availability. BMVs further contribute to bacteria as mediators in different interactions, with either other bacterial species or their hosts. In short, BMVs extend and deliver phenotypic traits that can have ecological and evolutionary value to both their producers and the ecosystem as a whole.

Immunomodulatory roles and novel applications of bacterial membrane vesicles

Bacteria release extracellular vesicles (EVs) known as bacterial membrane vesicles (BMVs) during their normal growth. Gram-negative bacteria produce BMVs termed outer membrane vesicles (OMVs) that are composed of a range of biological cargo and facilitate numerous bacterial functions, including promoting pathogenesis and mediating disease in the host. By contrast, less is understood about BMVs produced by Gram-positive bacteria, which are referred to as membrane vesicles (MVs), however their contribution to mediating bacterial pathogenesis has recently become evident. In this review, we summarise the mechanisms whereby BMVs released by Gram-negative and Gram-positive bacteria are produced, in addition to discussing their key functions in promoting bacterial survival, mediating pathogenesis and modulating host immune responses. Furthermore, we discuss the mechanisms whereby BMVs produced by both commensal and pathogenic organisms can enter host cells and interact with innate immune receptors, in addition to how they modulate host innate and adaptive immunity to promote immunotolerance or drive the onset and progression of disease. Finally, we highlight current and emerging applications of BMVs in vaccine design, biotechnology and cancer therapeutics.

Outer Membrane Vesicle Induction and Isolation for Vaccine Development

Gram-negative bacteria release vesicular structures from their outer membrane, so called outer membrane vesicles (OMVs). OMVs have a variety of functions such as waste disposal, communication, and antigen or toxin delivery. These vesicles are the promising structures for vaccine development since OMVs carry many surface antigens that are identical to the bacterial surface. However, isolation is often difficult and results in low yields. Several methods to enhance OMV yield exist, but these do affect the resulting OMVs. In this review, our current knowledge about OMVs will be presented. Different methods to induce OMVs will be reviewed and their advantages and disadvantages will be discussed. The effects of the induction and isolation methods used in several immunological studies on OMVs will be compared. Finally, the challenges for OMV-based vaccine development will be examined and one example of a successful OMV-based vaccine will be presented.

Transcriptome Profiling of Staphylococcus aureus Associated Extracellular Vesicles Reveals Presence of Small RNA-Cargo

Bacterial extracellular vesicles (EVs) have a vital role in bacterial pathogenesis. However, to date, the small RNA-cargo of EVs released by the opportunistic pathogen Staphylococcus aureus has not been characterized. Here, we shed light on the association of small RNAs with EVs secreted by S. aureus MSSA476 cultured in iron-depleted bacteriologic media supplemented with a subinhibitory dosage of vancomycin to mimic infection condition. Confocal microscopy analysis on intact RNase-treated EVs indicated that RNA is associated with EV particles. Transcriptomic followed by bioinformatics analysis of EV-associated RNA revealed the presence of potential gene regulatory small RNAs and high levels of tRNAs. Among the EV-associated enriched small RNAs were SsrA, RsaC and RNAIII. Our finding invites new insights into the potential role of EV-associated RNA as a modulator of host-pathogen interaction.

Real-time tracking of bacterial membrane vesicles reveals enhanced membrane traffic upon antibiotic exposure

Membrane vesicles are ubiquitous carriers of molecular information. A broad understanding of the biological functions of membrane vesicles in bacteria remains elusive because of the imaging challenges during real-time in vivo experiments. Here, we provide a quantitative analysis of the motion of individual vesicles in living microbes using fluorescence microscopy, and we show that while vesicle free diffusion in the intercellular space is rare, vesicles mostly disperse along the bacterial surfaces. Most remarkably, when bacteria are challenged with low doses of antibiotics, vesicle production and traffic, quantified by instantaneous vesicle speeds and total traveled distance per unit time, are significantly enhanced. Furthermore, the enhanced vesicle movement is independent of cell clustering properties but rather is associated with a reduction of the density of surface appendages in response to antibiotics. Together, our results provide insights into the emerging field of spatial organization and dynamics of membrane vesicles in microcolonies.

Proteomic Analysis of Vesicle-Producing Pseudomonas aeruginosa PAO1 Exposed to X-Ray Irradiation

Ionizing irradiation kills pathogens by destroying nucleic acids without protein structure destruction. However, how pathogens respond to irradiation stress has not yet been fully elucidated. Here, we observed that Pseudomonas aeruginosa PAO1 could release nucleic acids into the extracellular environment under X-ray irradiation. Using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), X-ray irradiation was observed to induce outer membrane vesicle (OMV) formation in P. aeruginosa PAO1. The size distribution of the OMVs of the irradiated PAO1 was similar to that of the OMVs of the non-irradiated PAO1 according to nanoparticle tracking analysis (NTA). The pyocin-related proteins are involved in OMV production in P. aeruginosa PAO1 under X-ray irradiation conditions, and that this is regulated by the key SOS gene recA. The OMV production was significantly impaired in the irradiated PAO1 Δlys mutant, suggesting that Lys endolysin is associated with OMV production in P. aeruginosa PAO1 upon irradiation stress. Meanwhile, no significant difference in OMV production was observed between PAO1 lacking the pqsR, lasR, or rhlR genes and the parent strain, demonstrating that the irradiation-induced OMV biosynthesis of P. aeruginosa was independent of the Pseudomonas quinolone signal (PQS).

Membrane Vesicle Production as a Bacterial Defense Against Stress

Membrane vesicles are the nano-sized vesicles originating from membranes. The production of membrane vesicles is a common feature among bacteria. Depending on the bacterial growth phase and environmental conditions, membrane vesicles show diverse characteristics. Various physiological and ecological roles have been attributed to membrane vesicles under both homeostatic and stressful conditions. Pathogens encounter several stressors during colonization in the hostile environment of host tissues. Nutrient deficiency, the presence of antibiotics as well as elements of the host’s immune system are examples of stressors threatening pathogens inside their host. To combat stressors and survive, pathogens have established various defensive mechanisms, one of them is production of membrane vesicles. Pathogens produce membrane vesicles to alleviate the destructive effects of antibiotics or other types of antibacterial treatments. Additionally, membrane vesicles can also provide benefits for the wider bacterial community during infections, through the transfer of resistance or virulence factors. Hence, given that membrane vesicle production may affect the activities of antibacterial agents, their production should be considered when administering antibacterial treatments. Besides, regarding that membrane vesicles play vital roles in bacteria, disrupting their production may suggest an alternative strategy for battling against pathogens. Here, we aim to review the stressors encountered by pathogens and shed light on the roles of membrane vesicles in increasing pathogen adaptabilities in the presence of stress-inducing factors.

A Budding Relationship: Bacterial Extracellular Vesicles in the Microbiota-Gut-Brain Axis

The discovery of the microbiota-gut-brain axis has revolutionized our understanding of systemic influences on brain function and may lead to novel therapeutic approaches to neurodevelopmental and mood disorders. A parallel revolution has occurred in the field of intercellular communication, with the realization that endosomes, and other extracellular vesicles, rival the endocrine system as regulators of distant tissues. These two paradigms shifting developments come together in recent observations that bacterial membrane vesicles contribute to inter-kingdom signaling and may be an integral component of gut microbe communication with the brain. In this short review we address the current understanding of the biogenesis of bacterial membrane vesicles and the roles they play in the survival of microbes and in intra and inter-kingdom communication. We identify recent observations indicating that bacterial membrane vesicles, particularly those derived from probiotic organisms, regulate brain function. We discuss mechanisms by which bacterial membrane vesicles may influence the brain including interaction with the peripheral nervous system, and modulation of immune activity. We also review evidence suggesting that, unlike the parent organism, gut bacteria derived membrane vesicles are able to deliver cargo, including neurotransmitters, directly to the central nervous system and may thus constitute key components of the microbiota-gut-brain axis.

Insights Into Mechanisms of Antimicrobial Photodynamic Action Toward Biofilms Using Phenalen-1-One Derivatives as Photosensitizers

Introduction

In view of increasing resistance against antibiotics and antiseptics, antimicrobial photodynamic therapy (aPDT) may be a promising approach for use in dentistry. The aim of this study was to investigate the mechanism of action of aPDT with the phenalene-1-one derivatives SAPYR and SA-PN-05 as photosensitizers by evaluating bacterial ability to replicate, membrane integrity, metabolic activity, and formation of reactive oxygen species (ROS) in biofilms of Actinomyces naeslundii, Streptococcus mutans, and Escherichia coli.

Materials and Methods

Single-species biofilms (A. naeslundii, S. mutans, and E. coli) were cultured under aerobic conditions for 48 h followed by treatment with the photosensitizers SAPYR and SA-PN-05 at various concentrations (0, 50, 100, 500 μM) and different incubation periods of 5, 10, 20, and 30 min and subsequent irradiation for 10 min (Waldmann PIB 3000; λ_em = 360–600 nm; 50 mW/cm²; 30 J/cm²). Control samples were treated with dH₂O and kept in dark for the same periods. Bacterial ability to replicate was evaluated by colony forming unit (CFU) assay. The cytoplasmic membrane integrity was investigated by flow cytometry using SYBR Green and propidium iodide and visualized by scanning and transmission electron microscopy. For SAPYR, metabolic activity and formation of intracellular ROS after irradiation were evaluated via luminescence and fluorometric assays, respectively.

Results

SAPYR showed antimicrobial effects (>3 log₁₀ CFU reduction) on S. mutans after 5 min and on A. naeslundii after 20 min incubation and light activation. For E. coli, CFU reduction was >2 log₁₀ after 30 min of incubation. SA-PN-05 showed an antimicrobial effect after 5 min for all bacteria. Membrane damage upon aPDT with SAPYR was observed for E. coli, but not for S. mutans and A. naeslundii. Following treatment with SA-PN-05, irradiated samples and dark controls of all three species showed loss of membrane integrity. Luminescence and fluorometric assays showed a reduction in metabolic activity and an increase in formation of intracellular ROS in all three species upon aPDT treatment with SAPYR.

Conclusion

The observed loss in ability to replicate upon aPDT with SAPYR in single-species biofilms may be due to an increase in formation of intracellular ROS upon photodynamic treatment.

Therapeutic Effect and Mechanisms of the Novel Monosulfactam 0073

This study aimed to evaluate the antimicrobial activity of the novel monosulfactam 0073 against multidrug-resistant Gram-negative bacteria in vitro and in vivo and to characterize the mechanisms underlying 0073 activity. The in vitro activities of 0073, aztreonam, and the combination with avibactam were assessed by MIC and time-kill assays. The safety of 0073 was evaluated using 3-(4,5-dimethylthizol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and acute toxicity assays. Murine thigh infection and pneumonia models were employed to define in vivo efficacy. A penicillin-binding protein (PBP) competition assay and confocal microscopy were conducted. The inhibitory action of 0073 against β-lactamases was evaluated by the half-maximal inhibitory concentration (IC₅₀), and resistance development was evaluated via serial passage. The monosulfactam 0073 showed promising antimicrobial activity against Enterobacteriaceae, Pseudomonas aeruginosa, and Acinetobacter baumannii isolates producing metallo-β-lactamases (MBLs) and serine β-lactamases. In preliminary experiments, compound 0073 exhibited safety both in vitro and in vivo In the murine thigh infection model and the pneumonia models in which infection was induced by P. aeruginosa and Klebsiella pneumoniae, 0073 significantly reduced the bacterial burden. Compound 0073 targeted several PBPs and exerted inhibitory effects against some serine β-lactamases. Finally, 0073 showed a reduced propensity for resistance selection compared with that of aztreonam. The novel monosulfactam 0073 exhibited increased activity against β-lactamase-producing Gram-negative organisms compared with the activity of aztreonam and showed good safety profiles both in vitro and in vivo The underlying mechanisms may be attributed to the affinity of 0073 for several PBPs and its inhibitory activity against some serine β-lactamases. These data indicate that 0073 represents a potential treatment for infections caused by β-lactamase-producing multidrug-resistant bacteria.

Biofilm formation and extracellular microvesicles-The way of foodborne pathogens toward resistance

Almost all known foodborne pathogens are able to form biofilms as one of the strategies for survival under harsh living conditions, to ward off the inhibition and the disinfection during food production, transport and storage, as well as during cleaning and sanitation of corresponding facilities. Biofilms are communities where microbial cells live under constant intracellular interaction and communication. Members of the biofilm community are embedded into extracellular matrix that contains polysaccharides, DNA, lipids, proteins, and small molecules that protect microorganisms and enable their intercellular communication under stress conditions. Membrane vesicles (MVs) are produced by both Gram positive and Gram negative bacteria. These lipid membrane-enveloped nanoparticles play an important role in biofilm genesis and in communication between different biofilm members. Furthermore, MVs are involved in other important steps of bacterial life like cell wall modeling, cellular division, and intercellular communication. They also carry toxins and virulence factors, as well as nucleic acids and different metabolites, and play a key role in host infections. After entering host cells, MVs can start many pathologic processes and cause serious harm and cell death. Prevention and inhibition of both biofilm formation and shedding of MVs by foodborne pathogens has a very important role in food production, storage, and food safety in general. Better knowledge of biofilm formation and maintaining, as well as the role of microbial vesicles in this process and in the process of host cells' infection is essential for food safety and prevention of both food spoilage and host infection.

Extracellular Vesicles Influence the Growth and Adhesion of Staphylococcus epidermidis Under Antimicrobial Selective Pressure

Staphylococcus epidermidis causes infections associated with orthopedic implants due to its ability to establish persistent biofilms, making infections chronic and hard to treat. Extracellular vesicles (EVs) are part of the bacterial communication system, but the role of S. epidermidis-derived EVs in biofilm formation processes and survival is completely unknown. The aims of this study were (i) to investigate the effect of subinhibitory concentrations of antibiotics on vesiculation in S. epidermidis and evaluate the role of EVs in bacterial survival and adhesion under antimicrobial selective pressure and (ii) to evaluate whether EVs derived from a gentamicin-resistant S. epidermidis strain influence the susceptibility and adhesion of a gentamicin-susceptible strain. A gentamicin-susceptible (GEN^S) strain isolated from implant-associated osteomyelitis was cultured with EVs previously isolated from the same strain growing with subinhibitory concentrations of GEN (0, 0.03, and 0.06 μg × mL^–1) or with EVs from a gentamicin-resistant (GEN^R) strain. EVs were characterized regarding their size, number and protein content. The growth of S. epidermidis cultured with increasing concentrations of GEN (<=> MIC of 0.12 μg × mL^–1) was recorded, viability was determined by quantitative culturing and fluorescence staining, and biofilm biomass on polystyrene was quantified by crystal violet staining. Cells grown in subinhibitory concentrations of GEN produced a larger number of EVs of similar size but with greater protein content than cells grown in control (Ctrl) conditions (0 GEN). Under antimicrobial pressure, EVs promoted different mechanisms of antimicrobial tolerance depending on the EV and GEN concentrations. Cell adhesion to polystyrene decreased in the presence of 0 and 0.03 μg × mL^–1 GEN upon EV stimulation. Compared with Ctrl cells, cells treated with EVs from a GEN^R strain showed increased cell division during the exponential growth phase, faster maximal growth rate, shorter doubling time (8–33 min), and dramatically inhibited cell adhesion. These findings suggest that vesiculation in S. epidermidis is a survival response to subinhibitory concentrations of gentamicin. EVs may contribute to bacterial survival through their involvement (1) in the modulation of the growth rate, affecting cell division, and (2) in cell adhesion, decreasing cell attachment to polystyrene and glass.

Dissemination of the blaCTX-M-15 gene among Enterobacteriaceae via outer membrane vesicles

Background

Bacterial outer membrane vesicles (OMVs) are an emerging source of antibiotic resistance transfer but their role in the spread of the blaCTX-M-15 gene encoding the most frequent CTX-M ESBL in Enterobacteriaceae is unknown.

Objectives

To determine the presence of blaCTX-M-15 and other antibiotic resistance genes in OMVs of the CTX-M-15-producing MDR Escherichia coli O104:H4 outbreak strain and the ability of these OMVs to spread these genes among Enterobacteriaceae under different conditions.

Methods

OMV-borne antibiotic resistance genes were detected by PCR; OMV-mediated transfer of blaCTX-M-15 and the associated blaTEM-1 was quantified under laboratory conditions, simulated intraintestinal conditions and under ciprofloxacin stress; resistance to antibiotics and the ESBL phenotype were determined by the CLSI disc diffusion methods and the presence of pESBL by plasmid profiling and Southern blot hybridization.

Results

E. coli O104:H4 OMVs carried blaCTX-M-15 and blaTEM-1 located on the pESBL plasmid, but not chromosomal antibiotic resistance genes. The OMVs transferred blaCTX-M-15, blaTEM-1 and the associated pESBL into Enterobacteriaceae of different species. The frequencies of the OMV-mediated transfer were significantly increased under simulated intraintestinal conditions and under ciprofloxacin stress when compared with laboratory conditions. The ‘vesiculants’ (i.e. recipients that received the blaCTX-M-15- and blaTEM-1-harbouring pESBL via OMVs) acquired resistance to cefotaxime, ceftazidime and cefpodoxime and expressed the ESBL phenotype. They were able to further spread pESBL and the blaCTX-M-15 and blaTEM-1 genes via OMVs.

Conclusions

OMVs are efficient vehicles for dissemination of the blaCTX-M-15 gene among Enterobacteriaceae and may contribute to blaCTX-M-15 transfer in the human intestine.

Secretion and Delivery of Intestinal Pathogenic Escherichia coli Virulence Factors via Outer Membrane Vesicles

Outer membrane vesicles (OMVs) are nanoscale proteoliposomes secreted from the cell envelope of all Gram-negative bacteria. Originally considered as an artifact of the cell wall, OMVs are now recognized as a general secretion system, which serves to improve the fitness of bacteria and facilitate bacterial interactions in polymicrobial communities as well as interactions between the microbe and the host. In general, OMVs are released in increased amounts from pathogenic bacteria and have been found to harbor much of the contents of the parental bacterium. They mainly encompass components of the outer membrane and the periplasm including various virulence factors such as toxins, adhesins, and immunomodulatory molecules. Numerous studies have clearly shown that the delivery of toxins and other virulence factors via OMVs essentially influences their interactions with host cells. Here, we review the OMV-mediated intracellular deployment of toxins and other virulence factors with a special focus on intestinal pathogenic Escherichia coli. Especially, OMVs ubiquitously produced and secreted by enterohemorrhagic E. coli (EHEC) appear as a highly advanced mechanism for secretion and simultaneous, coordinated and direct delivery of bacterial virulence factors into host cells. OMV-associated virulence factors are not only stabilized by the association with OMVs, but can also often target previously unknown target structures and perform novel activities. The toxins are released by OMVs in their active forms and are transported via cell sorting processes to their specific cell compartments, where they can develop their detrimental effects. OMVs can be considered as bacterial “long distance weapons” that attack host tissues and help bacterial pathogens to establish the colonization of their biological niche(s), impair host cell function, and modulate the defense of the host. Thus, OMVs contribute significantly to the virulence of the pathogenic bacteria.

Development of novel nanoantibiotics using an outer membrane vesicle-based drug efflux mechanism

Conventionally used antibiotics are present in low concentrations at the infection site and require multiple administrations to sustain a continuous bactericidal effect, which not only increases their systemic toxicity but also results in bacterial drug resistance. In this study, we first identified an interesting drug resistance mechanism mediated by bacterial outer membrane vesicles (OMVs) and then designed novel antibiotic-loaded OMVs using this mechanism. We show that these antibiotic-loaded OMVs can effectively enter and kill pathogenic bacteria in vitro. In a mouse model of intestinal bacterial infection, one low-dose oral administration of antibiotic-loaded OMVs showed that the drug was retained in the intestine for 36 h, and no systemic spread was detected 12 h after drug administration. The antibiotic-loaded OMVs significantly reduced the bacterial load in the small intestine and feces of infected mice. Safety experiments confirmed that the antibiotic-loaded OMVs had excellent biocompatibility. This study extends the application range of OMVs and provides new ideas for the development of antibacterial drugs.

Extracellular membrane vesicles in the three domains of life and beyond

Cells from all three domains of life, Archaea, Bacteria and Eukarya, produce extracellular vesicles (EVs) which are sometimes associated with filamentous structures known as nanopods or nanotubes. The mechanisms of EV biogenesis in the three domains remain poorly understood, although studies in Bacteria and Eukarya indicate that the regulation of lipid composition plays a major role in initiating membrane curvature. EVs are increasingly recognized as important mediators of intercellular communication via transfer of a wide variety of molecular cargoes. They have been implicated in many aspects of cell physiology such as stress response, intercellular competition, lateral gene transfer (via RNA or DNA), pathogenicity and detoxification. Their role in various human pathologies and aging has aroused much interest in recent years. EVs can be used as decoys against viral attack but virus-infected cells also produce EVs that boost viral infection. Here, we review current knowledge on EVs in the three domains of life and their interactions with the viral world.

Comparative Genomic Analyses Reveal Core-Genome-Wide Genes Under Positive Selection and Major Regulatory Hubs in Outlier Strains of Pseudomonas aeruginosa

Genomic information for outlier strains of Pseudomonas aeruginosa is exiguous when compared with classical strains. We sequenced and constructed the complete genome of an environmental strain CR1 of P. aeruginosa and performed the comparative genomic analysis. It clustered with the outlier group, hence we scaled up the analyses to understand the differences in environmental and clinical outlier strains. We identified eight new regions of genomic plasticity and a plasmid pCR1 with a VirB/D4 complex followed by trimeric auto-transporter that can induce virulence phenotype in the genome of strain CR1. Virulence genotype analysis revealed that strain CR1 lacked hemolytic phospholipase C and D, three genes for LPS biosynthesis and had reduced antibiotic resistance genes when compared with clinical strains. Genes belonging to proteases, bacterial exporters and DNA stabilization were found to be under strong positive selection, thus facilitating pathogenicity and survival of the outliers. The outliers had the complete operon for the production of vibrioferrin, a siderophore present in plant growth promoting bacteria. The competence to acquire multidrug resistance and new virulence factors makes these strains a potential threat. However, we identified major regulatory hubs that can be used as drug targets against both the classical and outlier groups.

Secretion of Salmonella Pathogenicity Island 1-Encoded Type III Secretion System Effectors by Outer Membrane Vesicles in Salmonella enterica Serovar Typhimurium

Outer membrane vesicles (OMVs) are spherical membranous structures released by Gram-negative bacteria. Several bacterial pathogens utilize OMVs as vehicles for the delivery of virulence factors into host cells. Results of our previous study on proteomic analysis revealed that OMVs isolated from Salmonellaenterica serovar Typhimurium had virulence effectors that are known to be translocated by Salmonella pathogenicity island 1 (SPI-1)-encoded type III secretion system (T3SS1) into the host cell. In the present study, immunoblot analysis confirmed the secretion of the six T3SS1 effector proteins, namely SipB and SipC (translocators of T3SS1), and SipA, SopA, SopB, and SopE2 (effectors translocated by T3SS1), by OMVs. Results of proteinase K treatment revealed the localization of these T3SS1 effector proteins on the outer surface of OMVs. SipC and SopE2 were secreted by OMVs independent of the three secretion systems T3SS1, T3SS2, and flagella, signifying OMVs to be an alternative delivery system to T3SSs. T3SS1 effectors SipA, SipC, and SopE2 were internalized into the cytoplasm of the host cell by OMVs independent of cellular Salmonella–host cell contact. In epithelial cells, addition of OMVs harboring T3SS1 effectors stimulated the production of F-actin, thereby complementing the attenuated invasion of ΔsopE2 into host cells. These results suggest that S. Typhimurium might exploit OMVs as a long-distance vehicle to deliver T3SS1 effectors into the cytoplasm of the host cell independent of bacteria–host cell interaction.

Outer Membrane Vesicles Facilitate Trafficking of the Hydrophobic Signaling Molecule CAI-1 between Vibrio harveyi Cells

Many bacteria use extracellular signaling molecules to coordinate group behavior, a process referred to as quorum sensing (QS). However, some QS molecules are hydrophobic in character and are probably unable to diffuse across the bacterial cell envelope. How these molecules are disseminated between bacterial cells within a population is not yet fully understood. Here, we show that the marine pathogen Vibrio harveyi packages the hydrophobic QS molecule CAI-1, a long-chain amino ketone, into outer membrane vesicles. Electron micrographs indicate that outer membrane vesicles of variable size are predominantly produced and released into the surroundings during the stationary phase of V. harveyi, which correlates with the timing of CAI-1-dependent signaling. The large vesicles (diameter, <55 nm) can trigger a QS phenotype in CAI-1-nonproducing V. harveyi and Vibrio cholerae cells. Packaging of CAI-1 into outer membrane vesicles might stabilize the molecule in aqueous environments and facilitate its distribution over distances.IMPORTANCE Formation of membrane vesicles is ubiquitous among bacteria. These vesicles are involved in protein and DNA transfer and offer new approaches for vaccination. Gram-negative bacteria use hydrophobic signaling molecules, among others, for cell-cell communication; however, due to their hydrophobic character, it is unclear how these molecules are disseminated between bacterial cells. Here, we show that the marine pathogen Vibrio harveyi packages one of its QS molecules, the long-chain ketone CAI-1, into outer membrane vesicles (OMVs). Isolated CAI-1-containing vesicles trigger a QS phenotype in CAI-1 nonproducing V. harveyi and also in Vibrio cholerae cells. Packaging of CAI-1 into OMVs not only solubilizes, stabilizes, and concentrates this class of molecules, but facilitate their distribution between bacteria that live in aqueous environments.

Outer membrane vesicles for vaccination and targeted drug delivery

Extracellular vesicles (EVs) are cell membrane-derived compartments that spontaneously secrete from a wide range of cells and tissues. EVs have shown to be the carriers in delivering drugs and small interfering RNA. Among EVs, bacterial outer membrane vesicles (OMVs) recently have gained the interest in vaccine development and targeted drug delivery. In this review, we summarize the current discoveries of OMVs and their functions. In particular, we focus on the biogenesis of OMVs and their functions in bacterial virulence and pathogenesis. Furthermore, we discuss the applications of OMVs in vaccination and targeted drug delivery. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies Biology-Inspired Nanomaterials > Lipid-Based Structures.

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.

Immediate response mechanisms of Gram-negative solvent-tolerant bacteria to cope with environmental stress: cis-trans isomerization of unsaturated fatty acids and outer membrane vesicle secretion

Bacteria have evolved an array of adaptive mechanisms enabling them to survive and grow in the presence of different environmental stresses. These mechanisms include either modifications of the membrane or changes in the overall energy status, cell morphology, and cell surface properties. Long-term adaptations are dependent on transcriptional regulation, the induction of anabolic pathways, and cell growth. However, to survive sudden environmental changes, bacterial short-term responses are essential to keep the cells alive after the occurrence of an environmental stress factor such as heat shock or the presence of toxic organic solvents. Thus far, two main short-term responses are known. On the one hand, a fast isomerization of cis into trans unsaturated fatty leads to a quick rigidification of the cell membrane, a mechanism known in some genera of Gram-negative bacteria. On the other hand, a fast, effective, and ubiquitously present countermeasure is the release of outer membrane vesicles (OMVs) from the cell surface leading to a rapid increase in cell surface hydrophobicity and finally to the formation of cell aggregates and biofilms. These immediate response mechanisms just allow the bacteria to stay physiologically active and to employ long-term responses to assure viability upon changing environmental conditions. Here, we provide insight into the two aforementioned rapid adaptive mechanisms affecting ultimately the cell envelope of Gram-negative bacteria.