In vitro study of virulence potential of Acinetobacter baumannii outer membrane vesicles

The Combinatory Effects of Essential Oil from Lippia macrophylla on Multidrug Resistant Acinetobacter baumannii Clinical Isolates

To assess the antibacterial effectiveness of Lippia macrophylla essential oil (LMEO) against multidrug-resistant Acinetobacter baumannii isolates, both as a standalone treatment and in combination with conventional antibiotics. LMEO demonstrated a significant inhibitory effect on the growth of A. baumannii, with a minimum inhibitory concentration (MIC) below 500 μg/mL. Notably, LMEO was capable of reversing the antibiotic resistance of clinical isolates or reducing their MIC values when used in combination with antibiotics, showing synergistic (FICI≤0.5) or additive effects. The combination of LMEO and imipenem was particularly effective, displaying synergistic interactions for most isolates. Ultrastructural analyses supported these findings, revealing that the combination of LMEO+ceftazidime compromised the membrane integrity of the Acb35 isolate, leading to cytoplasmic leakage and increased formation of Outer Membrane Vesicles (OMVs). Taken together our results point for the use of LMEO alone or in combination as an antibacterial agent against A. baumannii. These findings offer promising avenues for utilizing LMEO as a novel antibacterial strategy against drug-resistant infections in healthcare settings, underscoring the potential of essential oils in enhancing antibiotic efficacy.

Recovery and Analysis of Bacterial Membrane Vesicle Nanoparticles from Human Plasma Using Dielectrophoresis

Bacterial membrane vesicle (BMV) nanoparticles are secreted naturally by bacteria throughout their lifecycle and are a rich source of biomarkers from the parent bacteria, but they are currently underutilized for clinical diagnostic applications, such as pathogen identification, due to the time-consuming and low-yield nature of traditional recovery methods required for analysis. The recovery of BMVs is particularly difficult from complex biological fluids. Here, we demonstrate a recovery method that uses dielectrophoretic (DEP) forces generated on electrokinetic microfluidic chips to isolate and analyze BMVs from human plasma. DEP takes advantage of the natural difference in dielectric properties between the BMVs and the surrounding plasma fluid to quickly and consistently collect these particles from as little as 25 µL of plasma. Using DEP and immunofluorescence staining of the LPS biomarker carried on BMVs, we have demonstrated a lower limit of detection of 4.31 × 109 BMVs/mL. The successful isolation of BMVs from human plasma using DEP, and subsequent on-chip immunostaining for biomarkers, enables the development of future assays to identify the presence of specific bacterial species by analyzing BMVs from small amounts of complex body fluid.

Survival and virulence of Acinetobacter baumannii in microbial mixtures

Acinetobacter species such as A. venetianus and A. guillouiae have been studied for various biotechnology applications, including bioremediation of recalcitrant and harmful environmental contaminants, as well as bioengineering of enzymes and diagnostic materials. Bacteria used in biotechnology are often combined with other microorganisms in mixtures to formulate efficacious commercial products. However, if the mixture contained a closely related Acinetobacter pathogen such as A. baumannii (Ab), it remains unclear whether the survival and virulence of Ab would be masked or augmented. This uncertainty poses a challenge in ensuring the safety of such biotechnology products, since Ab is one of the most significant pathogens for both hospital and community -acquired infections. This research aimed to investigate the growth and virulence of Ab within a mixture of 11 bacterial species formulated as a mock microbial mixture (MM). Growth challenges with environmental stressors (i.e., temperature, pH, sodium, iron, and antibiotics) revealed that Ab could thrive under diverse conditions except in the presence of ciprofloxacin. When cultured alone, Ab exhibited significantly more growth in the presence of almost all the environmental stressors than when it was co-incubated with the MM. During the exposure of A549 lung epithelial cells to the MM, Ab growth was stimulated compared to that in standard mammalian culture media. Cytotoxicity caused by Ab was suppressed in the presence of the MM. Lymphocytes were significantly reduced in mice exposed to Ab with or without MM via intravenous injection. The levels of the splenic cytokines IL-1α, IL-1β, MCP-1, and MIP-1α were significantly reduced 24 h after exposure to Ab + MM. This study demonstrated that the presence of the MM marginally but significantly reduced the growth and virulence of Ab, which has implications for the safety of mixtures of microorganisms for biotechnological applications. Furthermore, these findings expand our understanding of the virulence of Ab during host-pathogen interactions.

Loss of Lipooligosaccharide Synthesis in Acinetobacter baumannii Produces Changes in Outer Membrane Vesicle Protein Content

Outer membrane vesicles (OMVs) are nanostructures derived from the outer membrane of Gram-negative bacteria. We previously demonstrated that vaccination with endotoxin-free OMVs isolated from an Acinetobacter baumannii strain lacking lipooligosaccharide (LOS) biosynthesis, due to a mutation in lpxD, provides full protection in a murine sepsis model. The present study characterizes the protein content of highly-purified OMVs isolated from LOS-replete and LOS-deficient strains. Four purification methods were evaluated to obtain highly purified OMV preparations: ultracentrifugation, size exclusion chromatography (SEC), ultracentrifugation followed by SEC, and Optiprep™. OMVs from each method were characterized using nanoparticle tracking analysis and electron microscopy. OMVs from LOS-deficient and LOS-replete strains purified using the Optiprep™ method were subjected to LC-MS/MS analysis to determine protein content. Significant differences in protein composition between OMVs from LOS-deficient and LOS-replete strains were found. Computational analyses using Bepipred 3.0 and SEMA 2.0 indicated that the lack of LOS led to the overexpression of immunogenic proteins found in LOS-containing OMVs and the presence of immune-stimulating proteins absent in LOS-replete OMVs. These findings have important implications for developing OMV-based vaccines against A. baumannii, using both LOS-containing and LOS-free OMVs preparations.

Role of Legionella pneumophila outer membrane vesicles in host-pathogen interaction

Legionella pneumophila is an opportunistic intracellular pathogen that inhabits artificial water systems and can be transmitted to human hosts by contaminated aerosols. Upon inhalation, it colonizes and grows inside the alveolar macrophages and causes Legionnaires' disease. To effectively control and manage Legionnaires' disease, a deep understanding of the host-pathogen interaction is crucial. Bacterial extracellular vesicles, particularly outer membrane vesicles (OMVs) have emerged as mediators of intercellular communication between bacteria and host cells. These OMVs carry a diverse cargo, including proteins, toxins, virulence factors, and nucleic acids. OMVs play a pivotal role in disease pathogenesis by helping bacteria in colonization, delivering virulence factors into host cells, and modulating host immune responses. This review highlights the role of OMVs in the context of host-pathogen interaction shedding light on the pathogenesis of L. pneumophila. Understanding the functions of OMVs and their cargo provides valuable insights into potential therapeutic targets and interventions for combating Legionnaires' disease.

Amplification of microbial DNA from bacterial extracellular vesicles from human placenta

Introduction

The placenta is essential for fetal growth and survival and maintaining a successful pregnancy. The sterility of the placenta has been challenged recently; however, the presence of a placental microbiome has been controversial. We tested the hypothesis that the bacterial extracellular vesicles (BEVs) from Gram-negative bacteria as an alternate source of microbial DNA, regardless of the existence of a microbial community in the placenta.

Methods

Placentae from the term, not in labor Cesareans deliveries, were used for this study, and placental specimens were sampled randomly from the fetal side. We developed a protocol for the isolation of BEVs from human tissues and this is the first study to isolate the BEVs from human tissue and characterize them.

Results

The median size of BEVs was 130-140 nm, and the mean concentration was 1.8-5.5 × 1010 BEVs/g of the wet placenta. BEVs are spherical and contain LPS and ompA. Western blots further confirmed ompA but not human EVs markers ALIX confirming the purity of preparations. Taxonomic abundance profiles showed BEV sequence reads above the levels of the negative controls (all reagent controls). In contrast, the sequence reads in the same placenta were substantially low, indicating nothing beyond contamination (low biomass). Alpha-diversity showed the number of detected genera was significantly higher in the BEVs than placenta, suggesting BEVs as a likely source of microbial DNA. Beta-diversity further showed significant overlap in the microbiome between BEV and the placenta, confirming that BEVs in the placenta are likely a source of microbial DNA in the placenta. Uptake studies localized BEVs in maternal (decidual) and placental cells (cytotrophoblast), confirming their ability to enter these cells. Lastly, BEVs significantly increased inflammatory cytokine production in THP-1 macrophages in a high-dose group but not in the placental or decidual cells.

Conclusion

We conclude that the BEVs are normal constituents during pregnancy and likely reach the placenta through hematogenous spread from maternal body sites that harbor microbiome. Their presence may result in a low-grade localized inflammation to prime an antigen response in the placenta; however, insufficient to cause a fetal inflammatory response and adverse pregnancy events. This study suggests that BEVs can confound placental microbiome studies, but their low biomass in the placenta is unlikely to have any immunologic impact.

Emerging role of microbiota derived outer membrane vesicles to preventive, therapeutic and diagnostic proposes

The role of gut microbiota and its products in human health and disease is profoundly investigated. The communication between gut microbiota and the host involves a complicated network of signaling pathways via biologically active molecules generated by intestinal microbiota. Some of these molecules could be assembled within nanoparticles known as outer membrane vesicles (OMVs). Recent studies propose that OMVs play a critical role in shaping immune responses, including homeostasis and acute inflammatory responses. Moreover, these OMVs have an immense capacity to be applied in medical research, such as OMV-based vaccines and drug delivery. This review presents a comprehensive overview of emerging knowledge about biogenesis, the role, and application of these bacterial-derived OMVs, including OMV-based vaccines, OMV adjuvants characteristics, OMV vehicles (in conjugated vaccines), cancer immunotherapy, and drug carriers and delivery systems. Moreover, we also highlight the significance of the potential role of these OMVs in diagnosis and therapy.

Exosomes: Insights and therapeutic applications in cancer

Cancer refers to the division of abnormal cells at an uncontrollable rate that possesses the ability to infiltrate and destroy normal tissues. It frequently spreads to normal tissues throughout the body, a condition known as metastasis, which is a significant concern. It is the second leading cause of mortality globally and treatment therapy can assist in improving survival rates. Exosomes are the extracellular vesicles secreted by several cells that act as messengers between cells. When engineered, exosomes act as promising drug delivery vehicles that help achieve targeted action at the tumour site and reduce the limitations of conventional treatments such as castration, chemotherapy, radiation, etc. The present review provides an overview of exosomes, the biogenesis, sources, isolation methods and characterization. The current status and applications of chemotherapeutic agents loaded, engineered exosomes in cancer treatment were convoluted.

Preventative treatment with Fluorothiazinon suppressed Acinetobacter baumannii-associated septicemia in mice

The high prevalence of multidrug-resistant Acinetobacter baumannii has emerged as a serious problem in the treatment of nosocomial infections in the past three decades. Recently, we developed a new small-molecule inhibitor belonging to a class of 2,4-disubstituted-4H-[1,3,4]-thiadiazine-5-ones, Fluorothiazinon (FT, previously called CL-55). FT effectively suppressed the T3SS of Chlamydia spp., Pseudomonas aeruginosa, and Salmonella sp. without affecting bacterial growth in vitro. In this study, we describe that prophylactic use of FT for 4 days prior to challenge with resistant clinical isolates of A. baumannii (ABT-897-17 and 52TS19) suppressed septic infection in mice, resulting in improved survival, limited bacteraemia and decreased bacterial load in the organs of the mice. We show that FT had an inhibitory effect on A. baumannii biofilm formation in vitro and, to a greater extent, on biofilm maturation. In addition, FT inhibited Acinetobacter isolate-induced death of HeLa cells, which morphologically manifested as apoptosis. The mechanism of FT action on A. baumannii is currently being studied. FT may be a promising candidate for the development of a broad-spectrum anti-virulence drug to use in the prevention of nosocomial infections.

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.

The Contribution of Membrane Vesicles to Bacterial Pathogenicity in Cystic Fibrosis Infections and Healthcare Associated Pneumonia

Almost all bacteria secrete spherical membranous nanoparticles, also referred to as membrane vesicles (MVs). A variety of MV types exist, ranging from 20 to 400 nm in diameter, each with their own formation routes. The most well-known vesicles are the outer membrane vesicles (OMVs) which are formed by budding from the outer membrane in Gram-negative bacteria. Recently, other types of MVs have been discovered and described, including outer-inner membrane vesicles (OIMVs) and cytoplasmic membrane vesicles (CMVs). The former are mainly formed by a process termed endolysin-triggered cell lysis in Gram-negative bacteria, the latter are formed by Gram-positive bacteria. MVs carry a wide range of cargo, such as nucleic acids, virulence factors and antibiotic resistance components. Moreover, they are involved in a multitude of biological processes that increase bacterial pathogenicity. In this review, we discuss the functional aspects of MVs secreted by bacteria associated with cystic fibrosis and nosocomial pneumonia. We mainly focus on how MVs are involved in virulence, antibiotic resistance, biofilm development and inflammation that consequently aid these bacterial infections.

High fat diet induces microbiota-dependent silencing of enteroendocrine cells

Enteroendocrine cells (EECs) are specialized sensory cells in the intestinal epithelium that sense and transduce nutrient information. Consumption of dietary fat contributes to metabolic disorders, but EEC adaptations to high fat feeding were unknown. Here, we established a new experimental system to directly investigate EEC activity in vivo using a zebrafish reporter of EEC calcium signaling. Our results reveal that high fat feeding alters EEC morphology and converts them into a nutrient insensitive state that is coupled to endoplasmic reticulum (ER) stress. We called this novel adaptation 'EEC silencing'. Gnotobiotic studies revealed that germ-free zebrafish are resistant to high fat diet induced EEC silencing. High fat feeding altered gut microbiota composition including enrichment of Acinetobacter bacteria, and we identified an Acinetobacter strain sufficient to induce EEC silencing. These results establish a new mechanism by which dietary fat and gut microbiota modulate EEC nutrient sensing and signaling.

Toll-Like Receptors 2 and 4 Modulate Pulmonary Inflammation and Host Factors Mediated by Outer Membrane Vesicles Derived from Acinetobacter baumannii

Pneumonia due to Gram-negative bacteria is associated with high mortality. Acinetobacter baumannii is a Gram-negative bacterium that is associated with hospital-acquired and ventilator-associated pneumonia. Bacteria have been described to release outer membrane vesicles (OMVs) that are capable of mediating systemic inflammation. The mechanism by which A. baumannii OMVs mediate inflammation is not fully defined. We sought to investigate the roles that Toll-like receptors (TLRs) play in A. baumannii OMV-mediated pulmonary inflammation. We isolated OMVs from A. baumannii cultures and intranasally introduced the OMVs into mice. Intranasal introduction of A. baumannii OMVs mediated pulmonary inflammation, which is associated with neutrophil recruitment and weight loss. In addition, A. baumannii OMVs increased the release of several chemokines and cytokines in the mouse lungs. The proinflammatory responses were partially inhibited in TLR2- and TLR4-deficient mice compared to those of wild-type mice. This study highlights the important roles of TLRs in A. baumannii OMV-induced pulmonary inflammation in vivo.

Exosomes on the border of species and kingdom intercommunication

Over the last decades exosomes have become increasingly popular in the field of medicine. While until recently they were believed to be involved in the removal of obsolete particles from the cell, it is now known that exosomes are key players in cellular communication, carrying source-specific molecules such as proteins, growth factors, miRNA/mRNA, among others. The discovery that exosomes are not bound to intraspecies interactions, but are also capable of interkingdom communication, has once again revolutionized the field of exosomes research. A rapidly growing body of literature is shedding light at novel sources and participation of exosomes in physiological or regenerative processes, infection and disease. For the purpose of this review we have categorized 6 sources of interest (animal products, body fluids, plants, bacteria, fungus and parasites) and linked their innate roles to the clinics and potential medical applications, such as cell-based therapy, diagnostics or drug delivery.

Tug of war between Acinetobacter baumannii and host immune responses

Acinetobacter baumannii is an emerging nosocomial, opportunistic pathogen with growing clinical significance. Acinetobacter baumannii has an exceptional ability to rapidly develop drug resistance and to adhere to abiotic surfaces, including medical equipment, significantly promoting bacterial spread and also limiting our ability to control A. baumannii infections. Consequently, A. baumannii is frequently responsible for ventilator-associated pneumonia in clinical settings. In order to develop an effective treatment strategy, understanding host-pathogen interactions during A. baumannii infection is crucial. Various A. baumannii virulence factors have been identified as targets of host innate pattern-recognition receptors, which leads to activation of downstream inflammasomes to develop inflammatory responses, and the recruitment of innate immune effectors against A. baumannii infection. To counteract host immune attack, A. baumannii regulates its expression of different virulence factors. This review summarizes the significance of mechanisms of host-bacteria interaction, as well as different bacteria and host defense mechanisms during A. baumannii infection.

Analysis of colony phase variation switch in Acinetobacter baumannii clinical isolates

Reversible switching between opaque and translucent colony formation is a novel feature of Acinetobacter baumannii that has been associated with variations in the cell morphology, surface motility, biofilm formation, antibiotic resistance and virulence. Here, we assessed a number of phenotypic alterations related to colony switching in A. baumannii clinical isolates belonging to different multi-locus sequence types. Our findings demonstrated that these phenotypic alterations were mostly strain-specific. In general, the translucent subpopulations of A. baumannii produced more dense biofilms, were more piliated, and released larger amounts of outer membrane vesicles (OMVs). In addition, the translucent subpopulations caused reduced fertility of Caenorhabditis elegans. When assessed for effects on the immune response in RAW 264.7 macrophages, the OMVs isolated from opaque subpopulations of A. baumannii appeared to be more immunogenic than the OMVs from the translucent form. However, also the OMVs from the translucent subpopulations had the potential to evoke an immune response. Therefore, we suggest that OMVs may be considered for development of new immunotherapeutic treatments against A. baumannii infections.

Vesicle-Mediated Gene Transfer in Acinetobacter baumannii

The role of vesicle-mediated gene transfer in Acinetobacter baumannii populations has been investigated in the last decade. Importantly, outer membrane vesicles (OMVs) secreted from A. baumannii cells have proven to be efficient agents of transfer of antimicrobial resistance genes to other bacterial species. However, the measurement of vesicle-mediated transfer depends on many experimental parameters. Here, we describe an experimental method useful to study transfer of DNA via membrane vesicles of A. baumannii in various bacterial populations.

Bacterial outer membrane vesicles, a potential vaccine candidate in interactions with host cells based

Both Gram-Positive and Gram-Negative bacteria can secrete outer membrane vesicles (OMVs) in their growth and metabolism process. Originally, OMVs were considered as a by-product of bacterial merisis. However, many scientists have reported the important role of OMVs in many fields recently. In this review, we briefly introduce OMVs biological functions and then summarize the findings about the OMVs interactions with host cells. At last, we will make an expectation about the prospects of the application of OMVs as vaccines.

The antimicrobial cathelicidin peptide hlF(1-11) attenuates alveolar macrophage pyroptosis induced by Acinetobacter baumannii in vivo

Acinetobacter baumannii is a Gram-negative coccobacillus found primarily in hospital settings that has recently emerged as a source of hospital-acquired infections, including bacterial pneumonia. The hLF(1-11) peptide comprising the first 11 N-terminal residues of human lactoferrin exerts antimicrobial activity in vivo and was highly effective against multidrug-resistant A. baumannii strains in vitro and in vivo. Pyroptosis is a caspase-1-dependent inflammatory cell death process and is induced by various microbial infections. In the present study, we investigated the molecular mechanisms that regulate pyroptosis induced by A. baumannii in macrophages. Our results revealed that A. baumannii induced pyroptosis through caspase-1 activation and IL-1β production. We also found that caspase-1 activation and IL-1β maturation in A. baumannii-triggered pyroptotic cell death were reduced by hLF(1-11) treatment. Moreover, hLF(1-11) inhibited the A. baumannii-induced caspase-1 activation and pyroptosis of pulmonary alveolar macrophages in vivo.