How do extracellular pathogens cross the blood-brain barrier?

Bacterial clustering biomaterials as anti-infective therapies

In Nature, bacterial clustering by host-released peptides or nucleic acids is an evolutionarily conserved immune defense strategy employed to prevent adhesion of pathogenic microbes, which is prerequisite for most infections. Synthetic anti-adhesion strategies present as non-lethal means of targeting bacteria and may potentially be used to avoid resistance against antimicrobial therapies. From bacteria-agglutinating biomolecules discovered in nature to synthetic designs involving peptides, cationic polymers and nanoparticles, the modes of actions appear broad and unconsolidated. Herein, we present a critical review and update of the state-of-the-art in synthetic bacteria-clustering designs with proposition of a more streamlined nomenclature and classification. Overall, this review aims to consolidate the conceptual framework in the field of bacterial clustering and highlight its potentials as an avenue for discovering novel antibacterial biomaterials.

Differential transcriptome response of blood brain barrier spheroids to neuroinvasive Neisseria and Borrelia

Background

The blood-brain barrier (BBB), a highly regulated interface between the blood and the brain, prevents blood-borne substances and pathogens from entering the CNS. Nevertheless, pathogens like Neisseria meningitidis and Borrelia bavariensis can breach the BBB and infect the brain parenchyma. The self-assembling BBB-spheroids can simulate the cross talk occurring between the cells of the barrier and neuroinvasive pathogens.

Methods

BBB spheroids were generated by co-culturing human brain microvascular endothelial cells (hBMECs), pericytes and astrocytes. The BBB attributes of spheroids were confirmed by mapping the localization of cells, observing permeability of angiopep2 and non-permeability of dextran. Fluorescent Neisseria, Borrelia or E. coli (non-neuroinvasive) were incubated with spheroids to observe the adherence, invasion and spheroid integrity. Transcriptome analysis with NGS was employed to investigate the response of BBB cells to infections.

Results

hBMECs were localized throughout the spheroids, whereas pericytes and astrocytes were concentrated around the core. Within 1 hr of exposure, Neisseria and Borrelia adhered to spheroids, and their microcolonization increased from 5 to 24 hrs. Integrity of spheroids was compromised by both Neisseria and Borrelia, but not by E. coli infection. Transcriptome analysis revealed a significant change in the expression of 781 genes (467 up and 314 down regulated) in spheroids infected with Neisseria, while Borrelia altered the expression of 621 genes (225 up and 396 down regulated). The differentially expressed genes could be clustered into various biological pathways like cell adhesion, extracellular matrix related, metallothionines, members of TGF beta, WNT signaling, and immune response. Among the differentially expressed genes, 455 (48%) genes were inversely expressed during Neisseria and Borrelia infection.

Conclusion

The self-assembling spheroids were used to perceive the BBB response to neuroinvasive pathogens - Neisseria and Borrelia. Compromised integrity of spheroids during Neisseria and Borrelia infection as opposed to its intactness and non-adherence of E. coli (non-neuroinvasive) denotes the pathogen dependent fate of BBB. Genes categorized into various biological functions indicated weakened barrier properties of BBB and heightened innate immune response. Inverse expression of 48% genes commonly identified during Neisseria and Borrelia infection exemplifies unique response of BBB to varying neuropathogens.

Infection metallomics for critical care in the post-COVID era

Infection metallomics is a mass spectrometry (MS) platform we established based on the central concept that microbial metallophores are specific, sensitive, noninvasive, and promising biomarkers of invasive infectious diseases. Here we review the in vitro, in vivo, and clinical applications of metallophores from historical and functional perspectives, and identify under-studied and emerging application areas with high diagnostic potential for the post-COVID era. MS with isotope data filtering is fundamental to infection metallomics; it has been used to study the interplay between "frenemies" in hosts and to monitor the dynamic response of the microbiome to antibiotic and antimycotic therapies. During infection in critically ill patients, the hostile environment of the host's body activates secondary bacterial, mycobacterial, and fungal metabolism, leading to the production of metallophores that increase the pathogen's chance of survival in the host. MS can reveal the structures, stability, and threshold concentrations of these metal-containing microbial biomarkers of infection in humans and model organisms, and can discriminate invasive disease from benign colonization based on well-defined thresholds distinguishing proliferation from the colonization steady state.

Utilizing passive elements to break time reversibility at low Reynolds number: a swimmer with one activated element

In the realm of low Reynolds number, the shape-changing biological and artificial matters need to break time reversibility in the course of their strokes to achieve motility. This necessity is well described in the so-called scallop theorem. In this work, considering low Reynolds number, a novel and versatile swimmer is proposed as an example of a new scheme to break time reversibility kinematically and, in turn, produce net motion. The swimmer consists of one sphere as a cargo or carried body, joined by one activated link with time-varying length, to another perpendicular rigid link, as the support of two passively flapping disks, at its end. The disks are free to rotate between their fixed minimum and maximum angles. The system's motion in two dimensions is simulated, and the maneuverability of the swimmer is discussed. The minimal operating parameters for steering of the swimmer are studied, and the limits of the swimmer are identified. The introduced swimming mechanism can be employed as a simple model system for biological living matters as well as artificial microswimmers.

Downregulated pol-miR-140-3p induces the expression of the kinesin family member 5A against Streptococcus parauberis infection in olive flounder

MicroRNAs (miRNAs) are small non-coding RNAs that participate in various biological and cellular processes by regulating target gene expression. miRNAs are also known to play vital roles in the pathogenesis of various diseases, including infections, as well as the disease progression and defense responses. In this study, we examined the expression levels of pol-miR-140-3p and its target gene, kinesin family member 5A (KIF5A), in association with the Streptococcus parauberis (S. parauberis) infection, a major bacterial pathogen that causes streptococcosis in olive flounder (Paralichthys olivaceus). KIF5A is a heavy chain isoform of kinesin-1, which is known to be brain-specific, and this study is the first examination of KIF5A expression related to the regulation of miRNA in olive flounder (named PoKIF5A). There were significant differences in expression levels between infected and healthy olive flounder as the expression of pol-miR-140-3p in the infected fish was lower than that in the control, while the expression of PoKIF5A was higher in the infected fish than in the healthy controls. These contradictory results suggest that downregulated pol-miR-140-3p induces the expression of PoKIF5A against S. parauberis infection in olive flounder.

Cytokines in the Brain and Neuroinflammation: We Didn’t Starve the Fire!

In spite of the brain-protecting tissues of the skull, meninges, and blood-brain barrier, some forms of injury to or infection of the CNS can give rise to cerebral cytokine production and action and result in drastic changes in brain function and behavior. Interestingly, peripheral infection-induced systemic inflammation can also be accompanied by increased cerebral cytokine production. Furthermore, it has been recently proposed that some forms of psychological stress may have similar CNS effects. Different conditions of cerebral cytokine production and action will be reviewed here against the background of neuroinflammation. Within this context, it is important to both deepen our understanding along already taken paths as well as to explore new ways in which neural functioning can be modified by cytokines. This, in turn, should enable us to put forward different modes of cerebral cytokine production and action in relation to distinct forms of neuroinflammation.

Altered gene expression in human brain microvascular endothelial cells in response to the infection of influenza H1N1 virus

Influenza viruses not only cause respiratory illness, but also have been reported to elicit neurological manifestations following acute viral infection. The central nervous system (CNS) has a specific defense mechanism against pathogens structured by cerebral microvasculature lined with brain endothelial cells to form the blood–brain barrier (BBB). To investigate the response of human brain microvascular endothelial cells (hBMECs) to the Influenza A virus (IAV), we inoculated the cells with the A/WSN/33 (H1N1) virus. We then conducted an RNAseq experiment to determine the changes in gene expression levels and the activated disease pathways following infection. The analysis revealed an effective activation of the innate immune defense by inducing the pattern recognition receptors (PRRs). Along with the production of proinflammatory cytokines, we detected an upregulation of interferons and interferon-stimulated genes, such as IFN-β/λ, ISG15, CXCL11, CXCL3 and IL-6, etc. Moreover, infected hBMECs exhibited a disruption in the cytoskeletal structure both on the transcriptomic and cytological levels. The RNAseq analysis showed different pathways and candidate genes associated with the neuroactive ligand-receptor interaction, neuroinflammation, and neurodegenerative diseases, together with a predicted activation of the neuroglia. Likewise, some genes linked with the mitochondrial structure and function displayed a significantly altered expression. En masse, this data supports that hBMECs could be infected by the IAV, which induces the innate and inflammatory immune response. The results suggest that the influenza virus infection could potentially induce a subsequent aggravation of neurological disorders.

Do Periodontal Pathogens or Associated Virulence Factors Have a Deleterious Effect on the Blood-Brain Barrier, Contributing to Alzheimer's Disease?

The central nervous system (CNS) is protected by a highly selective barrier, the blood-brain barrier (BBB), that regulates the exchange and homeostasis of bloodborne molecules, excluding xenobiotics. This barrier forms the first line of defense by prohibiting pathogens from crossing to the CNS. Aging and chronic exposure of the BBB to pathogens renders it permeable, and this may give rise to pathology in the CNS such as Alzheimer's disease (AD). Researchers have linked pathogens associated with periodontitis to neuroinflammation and AD-like pathology in vivo and in vitro. Although the presence of periodontitis-associated bacteria has been linked to AD in several clinical studies as DNA and virulence factors were confirmed in brain samples of human AD subjects, the mechanism by which the bacteria traverse to the brain and potentially influences neuropathology is unknown. In this review, we present current knowledge about the association between periodontitis and AD, the mechanism whereby periodontal pathogens might provoke neuroinflammation and how periodontal pathogens could affect the BBB. We suggest future studies, with emphasis on the use of human in vitro models of cells associated with the BBB to unravel the pathway of entry for these bacteria to the CNS and to reveal the molecular and cellular pathways involved in initiating the AD-like pathology. In conclusion, evidence demonstrate that bacteria associated with periodontitis and their virulence factors are capable of inflecting damage to the BBB and have a role in giving rise to pathology similar to that found in AD.

Equivalent time active cavitation imaging

RATIONALE

Despite the development of a large number of neurologically active drugs, brain diseases are difficult to treat due to the inability of many drugs to penetrate the blood-brain barrier. High-intensity focused ultrasound blood-brain barrier opening in a site-specific manner could significantly expand the spectrum of available drug treatments. However, without monitoring, brain damage and off target effects can occur during these treatments. While some methods can monitor inertial cavitation, temperature increase, or passively monitor cavitation events, to the best of our knowledge none of them can actively and spatiotemporally map the high intensity focused ultrasound pressure field during treatment.

METHODS

Here we detail the development of a novel ultrasound imaging modality called Equivalent Time Active Cavitation Imaging capable of characterizing the high-intensity focused ultrasound pressure field through stable cavitation events across the field of view with an ultrafast active imaging setup. This work introduces 1) a novel plane wave sequence whose transmit delays increase linearly with transmit events enabling the sampling of high-frequency cavitation events, and 2) an algorithm allowing the filtration of the microbubble signal for pressure field mapping. The pressure measurements with our modality were first carried out in vitro for hydrophone comparison and then in vivo during blood-brain barrier opening treatment in mice.

RESULTS

This study demonstrates the ability of our modality to spatiotemporally characterize a modulation pressure field with an active imaging setup. The resulting pressure field mapping reveals a good correlation with hydrophone measurements. Further proof is provided experimentally in vivo with promising results.

CONCLUSION

This proof of concept establishes the first steps towards a novel ultrasound modality for monitoring focused ultrasound blood-brain barrier opening, allowing new possibilities for a safe and precise monitoring method.

Meningococcal disease: A paradigm of type-IV pilus dependent pathogenesis

Neisseria meningitidis (meningococcus) is a Gram-negative bacterium responsible for two devastating forms of invasive diseases: purpura fulminans and meningitis. Interaction with both peripheral and cerebral microvascular endothelial cells is at the heart of meningococcal pathogenesis. During the last two decades, an essential role for meningococcal type IV pili in vascular colonisation and disease progression has been unravelled. This review summarises 20 years of research on meningococcal type IV pilus-dependent virulence mechanisms, up to the identification of promising anti-virulence compounds that target type IV pili.

Transcriptomic analysis of human brain microvascular endothelial cells exposed to laminin binding protein (adhesion lipoprotein) and Streptococcus pneumoniae

Streptococcus pneumoniae invades the CNS and triggers a strong cellular response. To date, signaling events that occur in the human brain microvascular endothelial cells (hBMECs), in response to pneumococci or its surface adhesins are not mapped comprehensively. We evaluated the response of hBMECs to the adhesion lipoprotein (a laminin binding protein—Lbp) or live pneumococci. Lbp is a surface adhesin recently identified as a potential ligand, which binds to the hBMECs. Transcriptomic analysis was performed by RNA-seq of three independent biological replicates and validated with qRT-PCR using 11 genes. In total 350 differentially expressed genes (DEGs) were identified after infection with S. pneumoniae, whereas 443 DEGs when challenged with Lbp. Total 231 DEGs were common in both treatments. Integrative functional analysis revealed participation of DEGs in cytokine, chemokine, TNF signaling pathways and phagosome formation. Moreover, Lbp induced cell senescence and breakdown, and remodeling of ECM. This is the first report which maps complete picture of cell signaling events in the hBMECs triggered against S. pneumoniae and Lbp. The data obtained here could contribute in a better understanding of the invasion of pneumococci across BBB and underscores role of Lbp adhesin in evoking the gene expression in neurovascular unit.

Interactions and Signal Transduction Pathways Involved during Central Nervous System Entry by Neisseria meningitidis across the Blood-Brain Barriers

The Gram-negative diplococcus Neisseria meningitidis, also called meningococcus, exclusively infects humans and can cause meningitis, a severe disease that can lead to the death of the afflicted individuals. To cause meningitis, the bacteria have to enter the central nervous system (CNS) by crossing one of the barriers protecting the CNS from entry by pathogens. These barriers are represented by the blood–brain barrier separating the blood from the brain parenchyma and the blood–cerebrospinal fluid (CSF) barriers at the choroid plexus and the meninges. During the course of meningococcal disease resulting in meningitis, the bacteria undergo several interactions with host cells, including the pharyngeal epithelium and the cells constituting the barriers between the blood and the CSF. These interactions are required to initiate signal transduction pathways that are involved during the crossing of the meningococci into the blood stream and CNS entry, as well as in the host cell response to infection. In this review we summarize the interactions and pathways involved in these processes, whose understanding could help to better understand the pathogenesis of meningococcal meningitis.

Nanotechnology-Based Diagnostics and Therapy for Pathogen-Related Infections in the CNS

The central nervous system (CNS) encompasses the brain, spinal cord, and nerves, where both brain and spinal cord are safeguarded by the meninges. However, serious bacterial, viral, or fungal infection in the brain causes life-threatening diseases such as meningitis. Engineered nanostructures hold great promise for not only in the diagnosis but also for combating microbial drug resistance owing to their high surface area and innate antibacterial activity. We delineate several nanoparticle-based approaches to enhance the CNS delivery of drugs across the blood-brain barrier (BBB). While pathogens invade the CNS by phagocytosis or receptor (e.g., EphA2)-mediated transcytosis, most of the nanoparticles cross the BBB via receptor-mediated transcytosis (e.g., antibody, peptide, protein). We also provide our perspectives on the diagnostic pathways based on nanotechnology for the detection of pathogens in the brain, thereby opening up new therapeutic avenues.

Neurosurgical Practice During Coronavirus Disease 2019 (COVID-19) Pandemic

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is a highly contagious life-threatening condition with unprecedented impacts for worldwide societies and health care systems. Since the first detection in China, it has spread rapidly worldwide. The increased burden has substantially affected neurosurgical practice and intensive modifications have been required in surgical scheduling, inpatient and outpatient clinics, management of emergency cases, and even in academic activities. In some systems, nonoverlapping teams have been created to minimize transmission among health care workers. In cases of a massive burden, neurosurgeons may need to be reassigned to COVID-19 wards, or teams from other regions may need to be sent to severely affected areas. Recommendations are as following. In outpatient practice, if possible, appointments should be undertaken via telemedicine. All staff assigned to the non-COVID treatment unit should be clothed in level 1 personal protective equipment. If possible, postponement is recommended for operations that do not require urgent or emergent intervention. All patients indicated for surgery must receive COVID-19 screening, including a nasopharyngeal swab and thorax computed tomography. Level 2 protection measures are appropriate during COVID-19-negative patients' operations. Operations of COVID-19-positive patients and emergency operations, in which screening cannot be obtained, should be performed after level 3 protective measures. During surgery, the use of high-speed drills and electrocautery should be reduced to minimize aerosol production. Screening is crucial in all patients because the surgical outcome is highly mortal in patients with COVID-19. All educational and academic conferences can be undertaken as virtual webinars.

A novel method for identifying and distinguishing Cryptococcus neoformans and Cryptococcus gattii by surface-enhanced Raman scattering using positively charged silver nanoparticles

There are approximately 1 million cryptococcal infections per year among HIV+ individuals, resulting in nearly 625,000 deaths. Cryptococcus neoformans and Cryptococcus gattii are the two most common species that cause human cryptococcosis. These two species of Cryptococcus have differences in pathogenicity, diagnosis, and treatment. Cryptococcal infections are usually difficult to identify because of their slow growth in vitro. In addition, the long detection cycle of Cryptococcus in clinical specimens makes the diagnosis of Cryptococcal infections difficult. Here, we used positively charged silver nanoparticles (AgNPs⁺) as a substrate to distinguish between C. neoformans and C. gattii in clinical specimens directly via surface-enhanced Raman scattering (SERS) and spectral analysis. The AgNPs⁺ self-assembled on the surface of the fungal cell wall via electrostatic aggregation, leading to enhanced SERS signals that were better than the standard substrate negatively charged silver nanoparticles (AgNPs). The SERS spectra could also be used as a sample database in the multivariate analysis via orthogonal partial least-squares discriminant analysis. This novel SERS detection method can clearly distinguish between the two Cryptococcus species using principal component analysis. The accuracy of the training data and test data was 100% after a tenfold crossover validation.

Neisseria meningitidis Induces Pathology-Associated Cellular and Molecular Changes in Trigeminal Schwann Cells

Neisseria meningitidis, a common cause of sepsis and bacterial meningitis, infects the meninges and central nervous system (CNS), primarily via paracellular traversal across the blood-brain barrier (BBB) or blood-cerebrospinal fluid barrier. N. meningitidis is often present asymptomatically in the nasopharynx, and the nerves extending between the nasal cavity and the brain constitute an alternative route by which the meningococci may reach the CNS. To date, the cellular mechanisms involved in nerve infection are not fully understood. Peripheral nerve glial cells are phagocytic and are capable of eliminating microorganisms, but some pathogens may be able to overcome this protection mechanism and instead infect the glia, causing cell death or pathology. Here, we show that N. meningitidis readily infects trigeminal Schwann cells (the glial cells of the trigeminal nerve) in vitro in both two-dimensional and three-dimensional cell cultures. Infection of trigeminal Schwann cells may be one mechanism by which N. meningitidis is able to invade the CNS. Infection of the cells led to multinucleation and the appearance of atypical nuclei, with the presence of horseshoe nuclei and the budding of nuclei increasing over time. Using sequential window acquisition of all theoretical mass spectra (SWATH-MS) proteomics followed by bioinformatics pathway analysis, we showed that N. meningitidis induced protein alterations in the glia that were associated with altered intercellular signaling, cell-cell interactions, and cellular movement. The analysis also suggested that the alterations in protein levels were consistent with changes occurring in cancer. Thus, infection of the trigeminal nerve by N. meningitidis may have ongoing adverse effects on the biology of Schwann cells, which may lead to pathology.

Transcriptome analysis of human brain microvascular endothelial cells response to Neisseria meningitidis and its antigen MafA using RNA-seq

Interaction of Neisseria meningitidis (NM) with human brain microvascular endothelial cells (hBMECs) initiates of multiple cellular processes, which allow bacterial translocation across the blood-brain barrier (BBB). NM is equipped with several antigens, which interacts with the host cell receptors. Recently we have shown that adhesin MafA (UniProtKB-X5EG71), relatively less studied protein, is one of those surface exposed antigens that adhere to hBMECs. The present study was designed to comprehensively map the undergoing biological processes in hBMECs challenged with NM or MafA using RNA sequencing. 708 and 726 differentially expressed genes (DEGs) were identified in hBMECs exposed to NM and MafA, respectively. Gene ontology analysis of the DEGs revealed that several biological processes, which may alter the permeability of BBB, were activated. Comparative analysis of DEGs revealed that MafA, alike NM, might provoke TLR-dependent pathway and augment cytokine response. Moreover, both MafA and NM were able to induce genes involved in cell surface modifications, endocytosis, extracellular matrix remodulation and anoikis/apoptosis. In conclusion, this study for the first time describes effect of NM on the global gene expression in hBMECs using high-throughput RNA-seq. It also presents ability of MafA to induce gene expression, which might aid NM in breaching the BBB.

Virulence Factors of Meningitis-Causing Bacteria: Enabling Brain Entry across the Blood-Brain Barrier

Infections of the central nervous system (CNS) are still a major cause of morbidity and mortality worldwide. Traversal of the barriers protecting the brain by pathogens is a prerequisite for the development of meningitis. Bacteria have developed a variety of different strategies to cross these barriers and reach the CNS. To this end, they use a variety of different virulence factors that enable them to attach to and traverse these barriers. These virulence factors mediate adhesion to and invasion into host cells, intracellular survival, induction of host cell signaling and inflammatory response, and affect barrier function. While some of these mechanisms differ, others are shared by multiple pathogens. Further understanding of these processes, with special emphasis on the difference between the blood-brain barrier and the blood-cerebrospinal fluid barrier, as well as virulence factors used by the pathogens, is still needed.

Cryptococcal Meningitis and Anti-virulence Therapeutic Strategies

Fungal infections of the central nervous system are responsible for significant morbidity and mortality. Cryptococcus neoformans (Cn) is the primary cause of fungal meningitis. Infection begins in the lung after inhalation of fungal spores but often spreads to other organs, particularly the brain in immunosuppressed individuals. Cn’s ability to survive phagocytosis and endure the onslaught of oxidative attack imposed by the innate immune response facilitates dissemination to the central nervous system (CNS). Despite the success of Cn at bypassing innate immunity, entry into the heavily protected brain requires that Cn overwhelm the highly restricted blood-brain barrier (BBB). This is a formidable task but mounting evidence suggests that Cn expresses surface-bound and secreted virulence factors including urease, metalloprotease, and hyaluronic acid that can undermine the BBB. In addition, Cn can exploit multiple routes of entry to gain access to the CNS. In this review, we discuss the cellular and molecular interface of Cn and the BBB, and we propose that the virulence factors mediating BBB crossing could be targeted for the development of anti-virulence drugs aimed at preventing fungal colonization of the CNS.

Gold nanoparticles: A plausible tool to combat neurological bacterial infections in humans

Management of bacterial infections of central nervous system is a major challenge for the scientists all over the world. Despite the development of various potential drugs, the issue of central nervous system infections persists in the society. The main constraint is the delivery of drugs across the blood brain barrier and only a few drugs after meeting the stringent criteria could cross the blood brain barrier. On the other hand, certain bacterial pathogens could easily enter the brain by using several factors and mechanisms by crossing the blood brain barriers. Interestingly, in the recent past, gold nanoparticles have shown immense potential to overcome the issues associated with the treatment of central nervous system infections, especially due to their inherent ability to cross the blood brain barrier. Initially, the present review summarized the recent updates on the pathogenesis and factors involved in neurological bacterial infections, including the mechanism used by bacterial pathogens to cross the blood brain barriers. Thereafter, the emphasis of the review was on providing current information on gold nanoparticles pertinent to their applicability for the treatment of neurological infections. After discussing the background of neurological bacterial infections, the characteristic features, antibacterial properties, mechanisms of antibacterial action and ability to cross the blood brain barrier of gold nanoparticles have been summarized. Some of the features of gold nanoparticles that make them an ideal candidate for brain delivery are biocompatibity, stability, ability to get synthesized in different sizes with facile methods, surface affinity towards various functional groups, spontaneous crossing of blood brain barrier without applying any external field and most importantly, easy non-invasive tracing by CT imaging. The current updates on the development of gold nanoparticles based therapeutic strategies for the prevention and treatment of central nervous system infections have been discussed in the present study. However, further investigation would be required to translate these preclinical outcomes into clinical applications. Nevertheless, we could safely state that the information gathered and discussed in the present review would benefit the scientists working in the field of neuro-nanotechnology.

Brucella abortus Traverses Brain Microvascular Endothelial Cells Using Infected Monocytes as a Trojan Horse

Neurobrucellosis is an inflammatory disease caused by the invasion of Brucella spp. to the central nervous system (CNS). The pathogenesis of the disease is not well characterized; however, for Brucella to gain access to the brain parenchyma, traversing of the blood-brain barrier (BBB) must take place. To understand the CNS determinants of the pathogenesis of B. abortus, we have used the in vitro BBB model of human brain microvascular endothelial cells (HBMEC) to study the interactions between B. abortus and brain endothelial cells. In this study, we showed that B. abortus is able to adhere and invade HBMEC which was dependent on microtubules, microfilaments, endosome acidification and de novo protein synthesis. After infection, B. abortus rapidly escapes the endosomal compartment of HBMEC and forms a replicative Brucella-containing vacuole that involves interactions with the endoplasmic reticulum. Despite the ability of B. abortus to invade and replicate in HBMEC, the bacterium was unable by itself to traverse HBMEC, but could traverse polarized HBMEC monolayers within infected monocytes. Importantly, infected monocytes that traversed the HBMEC monolayer were a bacterial source for de novo infection of glial cells. This is the first demonstration of the mechanism whereby B. abortus is able to traverse the BBB and infect cells of the CNS. These results may have important implications in our understanding of the pathogenesis of neurobrucellosis.

Crossing the Blood-Brain Barrier by Neuroinvasive Pathogens

The penetration of the blood-brain barrier (BBB) and invasion of the central nervous system (CNS) are important steps for all neuroinvasive pathogens. All of the ways of pathogens passing through the BBB are still unclear. Among known pathways, pathogen traversal can occur paracellularly, transcellularly or using a “Trojan horse” mechanism. The first step of translocation across the BBB is the interactions of the pathogen’s ligands with the receptors of the host brain cells. Lyme disease, the most common vector-borne disease in the temperate zones of Europe and North America, are caused by Borreliella species (former Borrelia burgdorferi sensu lato) that affects the peripheral and the CNS. In this review, we have presented various pathogen interactions with endothelial cells, which allow the disruption of the BBB so that the pathogens can pass across the BBB.

Genome-Wide Identification by Transposon Insertion Sequencing of Escherichia coli K1 Genes Essential for In Vitro Growth, Gastrointestinal Colonizing Capacity, and Survival in Serum

Escherichia coli K1 strains are major causative agents of invasive disease of newborn infants. The age dependency of infection can be reproduced in neonatal rats. Colonization of the small intestine following oral administration of K1 bacteria leads rapidly to invasion of the blood circulation; bacteria that avoid capture by the mesenteric lymphatic system and evade antibacterial mechanisms in the blood may disseminate to cause organ-specific infections such as meningitis. Some E. coli K1 surface constituents, in particular the polysialic acid capsule, are known to contribute to invasive potential, but a comprehensive picture of the factors that determine the fully virulent phenotype has not emerged so far. We constructed a library and constituent sublibraries of ∼775,000 Tn5 transposon mutants of E. coli K1 strain A192PP and employed transposon-directed insertion site sequencing (TraDIS) to identify genes required for fitness for infection of 2-day-old rats. Transposon insertions were lacking in 357 genes following recovery on selective agar; these genes were considered essential for growth in nutrient-replete medium. Colonization of the midsection of the small intestine was facilitated by 167 E. coli K1 gene products. Restricted bacterial translocation across epithelial barriers precluded TraDIS analysis of gut-to-blood and blood-to-brain transits; 97 genes were required for survival in human serum. This study revealed that a large number of bacterial genes, many of which were not previously associated with systemic E. coli K1 infection, are required to realize full invasive potential.

IMPORTANCEEscherichia coli K1 strains cause life-threatening infections in newborn infants. They are acquired from the mother at birth and colonize the small intestine, from where they invade the blood and central nervous system. It is difficult to obtain information from acutely ill patients that sheds light on physiological and bacterial factors determining invasive disease. Key aspects of naturally occurring age-dependent human infection can be reproduced in neonatal rats. Here, we employ transposon-directed insertion site sequencing to identify genes essential for the in vitro growth of E. coli K1 and genes that contribute to the colonization of susceptible rats. The presence of bottlenecks to invasion of the blood and cerebrospinal compartments precluded insertion site sequencing analysis, but we identified genes for survival in serum.

The blood-brain barrier internalises Cryptococcus neoformans via the EphA2-tyrosine kinase receptor

Cryptococcus neoformans is an opportunistic fungal pathogen that causes life-threatening meningitis most commonly in populations with impaired immunity. Here, we resolved the transcriptome of the human brain endothelium challenged with C. neoformans to establish whether C. neoformans invades the CNS by co-opting particular signalling pathways as a means to promote its own entry. Among the 5 major pathways targeted by C. neoformans, the EPH-EphrinA1 (EphA2) tyrosine kinase receptor-signalling pathway was examined further. Silencing the EphA2 receptor transcript in a human brain endothelial cell line or blocking EphA2 activity with an antibody or chemical inhibitor prevented transmigration of C. neoformans in an in vitro model of the blood-brain barrier (BBB). In contrast, treating brain endothelial cells with an EphA2 chemical agonist or an EphA2 ligand promoted greater migration of fungal cells across the BBB. C. neoformans activated the EPH-tyrosine kinase pathway through a CD44-dependent phosphorylation of EphA2, promoting clustering and internalisation of EphA2 receptors. Moreover, HEK293T cells expressing EphA2 revealed an association between EphA2 and C. neoformans that boosted internalisation of C. neoformans. Collectively, the results suggest that C. neoformans promotes EphA2 activity via CD44, and this in turn creates a permeable barrier that facilitates the migration of C. neoformans across the BBB.

Molecular mechanisms involved in the interaction of Neisseria meningitidis with cells of the human blood-cerebrospinal fluid barrier

Neisseria meningitidis is one of the most common aetiological agents of bacterial meningitis, affecting predominantly children and young adults. The interaction of N. meningitidis with human endothelial cells lining blood vessels of the blood-cerebrospinal fluid barrier (B-CSFB) is critical for meningitis development. In recent decades, there has been a significant increase in understanding of the molecular mechanisms involved in the interaction of N. meningitidis with brain vascular cells. In this review, we will describe how N. meningitidis adheres to the brain vasculature, may enter inside these cells, hijack receptor signalling pathways and alter host-cell responses in order to traverse the B-CSFB.

Interaction of factor H-binding protein of Streptococcus suis with globotriaosylceramide promotes the development of meningitis

Streptococcus suis is an important emerging zoonotic agent that causes acute bacterial meningitis in humans with high mortality and morbidity. Our previous work showed that factor H-binding protein (Fhb) contributed to virulence of S. suis, but the role of Fhb in the development of S. suis meningitis remained unclear. In this study, we demonstrated for the first time that Fhb contributed to the traversal of S. suis across the human blood-brain barrier by allelic-exchange mutagenesis, complementation and specific antibody blocking studies. We also showed that globotriaosylceramide (Gb3), the receptor of Fhb, was involved in this process and affected S. suis infection-induced activation of myosin light chain 2 through Rho/ROCK signaling in hCMEC/D3 cells. Using a murine model of S. suis meningitis, we further demonstrated that Gb3-deficiency prevented the mice from developing severe brain inflammation or injury. Our results demonstrate that the Fhb-Gb3 interaction plays an important role in the development of S. suis meningitis and might be a potential therapeutic target against S. suis infection.

The complete genome sequence of Cronobacter sakazakii ATCC 29544T, a food-borne pathogen, isolated from a child's throat

Background

Cronobacter sakazakii is an emerging opportunistic pathogen that is associated with rare but life-threatening cases of severe diseases: meningitis, necrotizing enterocolitis, and sepsis in premature and full-term infants. However, the pathogenesis mechanism of this pathogen remains largely unknown. To determine its pathogenesis at the genomic level, the genome of C. sakazakii ATCC 29544^T was completely sequenced and analyzed.

Results

The genomic DNA, containing a circular chromosome and three plasmids, is composed of 4,511,265 bp with a GC content of 56.71%, containing 4380 predicted open reading frames (ORFs), 22 rRNA genes, and 83 tRNA genes. The plasmids, designated pCSK29544_p1, pCSK29544_p2, and pCSK29544_p3, were 93,905-bp, 4938-bp, and 53,457-bp with GC contents of 57.02, 54.88, and 50.07%, respectively. They were also predicted to have 72, 6, and 57 ORFs without RNA genes.

Conclusions

The strain ATCC 29544^T genome has ompA and ibeB-homologous cusC genes, probably associated with the invasion of human brain microvascular endothelial cells (BMECs). In addition, gene clusters for siderophore production (iucABCD/iutA) and the related transport system (eitCBAD) were detected in pCSK29544_p1 plasmid, indicating better iron uptake ability for survival. Furthermore, to survive under extremely dry condition like milk powder, this genome has gene clusters for biosynthesis of capsular proteins (CSK29544_00281-00284) and cellulose (CSK29544_01124-01127) for biofilm formation and a gene cluster for utilization of sialic acid in the milk (nanKTAR). The genome information of C. sakazakii ATCC 29544^T would provide further understanding of its pathogenesis at the molecular level for the regulation of pathogenicity and the development of a rapid detection method using biomarkers.

Electronic supplementary material

The online version of this article (doi:10.1186/s13099-016-0150-0) contains supplementary material, which is available to authorized users.

Blood-brain barrier disruption during spontaneous canine visceral leishmaniasis

Visceral leishmaniasis is a complex disease caused by Leishmania infantum, and in dogs, besides the classical symptoms, there are descriptions of inflammatory alterations in the brain. Brain inflammation is a strictly controlled process, and as the brain counts on the efficiency of the blood-brain barrier (BBB), we aimed to assess BBB integrity in dogs with spontaneous visceral leishmaniasis. Therefore, we evaluated markers in the cerebrospinal fluid (CSF) and in brain tissue related to BBB disruption and brain inflammation. Elevated albumin quota revealed BBB breakdown, corroborated by increased concentrations of anti-Leishmania antibodies in the CSF. In the brain, albumin and IgG staining formed halos around blood vessels, a classical indicator of BBB leakage. Soluble IgG was also detected in the choroid plexus and ependyma, and in these structures, IgG stained random resident cells. IgG(+) cells and Fcγ-RI(+) cells were identified in the choroid plexus, ependyma and perivascular in the brain parenchyma. The data support the occurrence of BBB disruption in dogs with spontaneous visceral leishmaniasis, and IgG as a key molecule that is capable of initiating and/or maintaining the inflammatory stimuli in the nervous milieu and the CSF as an important disseminator of inflammatory stimuli within the CNS.

Neuroinvasion and Inflammation in Viral Central Nervous System Infections

Neurotropic viruses can cause devastating central nervous system (CNS) infections, especially in young children and the elderly. The blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB) have been described as relevant sites of entry for specific viruses as well as for leukocytes, which are recruited during the proinflammatory response in the course of CNS infection. In this review, we illustrate examples of established brain barrier models, in which the specific reaction patterns of different viral families can be analyzed. Furthermore, we highlight the pathogen specific array of cytokines and chemokines involved in immunological responses in viral CNS infections. We discuss in detail the link between specific cytokines and chemokines and leukocyte migration profiles. The thorough understanding of the complex and interrelated inflammatory mechanisms as well as identifying universal mediators promoting CNS inflammation is essential for the development of new diagnostic and treatment strategies.

SILAC and LC-MS/MS identification of Streptococcus equi ssp. zooepidemicus proteins that contribute to mouse brain microvascular endothelial cell infection

Streptococcus equi ssp. zooepidemicus (SEZ) causes meningitis in both humans and animals. Some dissociative proteins of SEZ are cytotoxic to mouse brain microvascular endothelial cells (mBMECs) and may contribute to the penetration of SEZ across the blood-brain barrier (BBB). In this study, the ability of SEZ to penetrate across an in vitro BBB model was confirmed. We used stable isotope labeling with amino acids in cell culture (SILAC) to label SEZ proteins with heavy or light isotope-tagged amino acids, along with LC-MS/MS to determine which SEZ proteins were involved in interactions with mBMECs. The efficiency of SEZ protein isotope labeling was 94.7 %, which was sufficient for further analysis. Forty-nine labeled peptides were identified as binding to mBMECs, which matched to 25 SEZ proteins. Bioinformatic analysis indicated that most of these proteins were cytoplasmic. These proteins may have functions in breaching the host BBB, and some of them are known virulence factors in other bacteria. Indirect immunofluorescence results indicated that SEZ enolase had binding activity toward mBMECs. Protective test results showed that enolase was a protective antigen against SEZ infection. This research is the first application of SILAC combined with LC-MS/MS to identify SEZ proteins that may contribute to the infection of mBMECs and potentially show functions related to breaching the BBB. The outcomes provide many future avenues for research into the mechanism of SEZ-induced meningitis.

The role of genomic islands in Escherichia coli K1 interactions with intestinal and kidney epithelial cells

The completion of Escherichia coli K1 genome has identified several genomic islands that are present in meningitis-causing E. coli RS218 but absent in the non-pathogenic E. coli MG1655. In this study, the role of various genomic islands in E. coli K1 interactions with intestinal epithelial cells (Caco-2) and kidney epithelial cells (MA104) was determined. Using association assays, invasion assays, and intracellular survival assays, the findings revealed that the genomic island deletion mutants of RS218 related to P fimbriae, S fimbriae, F17-like fimbriae, non-fimbrial adhesins, Hek and hemagglutinin, protein secretion system (T1SS for hemolysin; T2SS; T5SS for antigen 43), Iro system and hmu system), invasins (CNF1, IbeA), toxins (α-hemolysin), K1 capsule biosynthesis, metabolism (d-serine catabolism, dihydroxyacetone, glycerol, and glyoxylate metabolism), prophage genes, showed reduced interactions with both cell types. Next, we determined the role of various genomic islands in E. coli K1 resistance to serum. When exposed to the normal human serum, the viability of the genomic island deletion mutants related to adhesins such as S fimbriae, P fimbriae, F17-like fimbriae, non-fimbrial adhesins, Hek and hemagglutinin, antigen 43 and T5SS for antigen 43, T2SS, and T1SS for hemolysin, Iro system and hmu system, prophage genes, metabolism (sugar metabolism and d-serine catabolism), K1 capsule biosynthesis, and invasins such as CNF1 was affected, suggesting their role in bacteremia. The characterization of these genomic islands should reveal mechanisms of E. coli K1 pathogenicity that could be of value as therapeutic targets.

Host-pathogen interactions in bacterial meningitis

Bacterial meningitis is a devastating disease occurring worldwide with up to half of the survivors left with permanent neurological sequelae. Due to intrinsic properties of the meningeal pathogens and the host responses they induce, infection can cause relatively specific lesions and clinical syndromes that result from interference with the function of the affected nervous system tissue. Pathogenesis is based on complex host–pathogen interactions, some of which are specific for certain bacteria, whereas others are shared among different pathogens. In this review, we summarize the recent progress made in understanding the molecular and cellular events involved in these interactions. We focus on selected major pathogens, Streptococcus pneumonia, S. agalactiae (Group B Streptococcus), Neisseria meningitidis, and Escherichia coli K1, and also include a neglected zoonotic pathogen, Streptococcus suis. These neuroinvasive pathogens represent common themes of host–pathogen interactions, such as colonization and invasion of mucosal barriers, survival in the blood stream, entry into the central nervous system by translocation of the blood–brain and blood–cerebrospinal fluid barrier, and induction of meningeal inflammation, affecting pia mater, the arachnoid and subarachnoid spaces.

HexR Controls Glucose-Responsive Genes and Central Carbon Metabolism in Neisseria meningitidis

Neisseria meningitidis, an exclusively human pathogen and the leading cause of bacterial meningitis, must adapt to different host niches during human infection. N. meningitidis can utilize a restricted range of carbon sources, including lactate, glucose, and pyruvate, whose concentrations vary in host niches. Microarray analysis of N. meningitidis grown in a chemically defined medium in the presence or absence of glucose allowed us to identify genes regulated by carbon source availability. Most such genes are implicated in energy metabolism and transport, and some are implicated in virulence. In particular, genes involved in glucose catabolism were upregulated, whereas genes involved in the tricarboxylic acid cycle were downregulated. Several genes encoding surface-exposed proteins, including the MafA adhesins and Neisseria surface protein A, were upregulated in the presence of glucose. Our microarray analysis led to the identification of a glucose-responsive hexR-like transcriptional regulator that controls genes of the central carbon metabolism of N. meningitidis in response to glucose. We characterized the HexR regulon and showed that the hexR gene is accountable for some of the glucose-responsive regulation; in vitro assays with the purified protein showed that HexR binds to the promoters of the central metabolic operons of the bacterium. Based on DNA sequence alignment of the target sites, we propose a 17-bp pseudopalindromic consensus HexR binding motif. Furthermore, N. meningitidis strains lacking hexR expression were deficient in establishing successful bacteremia in an infant rat model of infection, indicating the importance of this regulator for the survival of this pathogen in vivo.

IMPORTANCE

Neisseria meningitidis grows on a limited range of nutrients during infection. We analyzed the gene expression of N. meningitidis in response to glucose, the main energy source available in human blood, and we found that glucose regulates many genes implicated in energy metabolism and nutrient transport, as well as some implicated in virulence. We identified and characterized a transcriptional regulator (HexR) that controls metabolic genes of N. meningitidis in response to glucose. We generated a mutant lacking HexR and found that the mutant was impaired in causing systemic infection in animal models. Since N. meningitidis lacks known bacterial regulators of energy metabolism, our findings suggest that HexR plays a major role in its biology by regulating metabolism in response to environmental signals.

Bioluminescent imaging reveals novel patterns of colonization and invasion in systemic Escherichia coli K1 experimental infection in the neonatal rat

Key features of Escherichia coli K1-mediated neonatal sepsis and meningitis, such as a strong age dependency and development along the gut-mesentery-blood-brain course of infection, can be replicated in the newborn rat. We examined temporal and spatial aspects of E. coli K1 infection following initiation of gastrointestinal colonization in 2-day-old (P2) rats after oral administration of E. coli K1 strain A192PP and a virulent bioluminescent derivative, E. coli A192PP-lux2. A combination of bacterial enumeration in the major organs, two-dimensional bioluminescence imaging, and three-dimensional diffuse light imaging tomography with integrated micro-computed tomography indicated multiple sites of colonization within the alimentary canal; these included the tongue, esophagus, and stomach in addition to the small intestine and colon. After invasion of the blood compartment, the bacteria entered the central nervous system, with restricted colonization of the brain, and also invaded the major organs, in line with increases in the severity of symptoms of infection. Both keratinized and nonkeratinized surfaces of esophagi were colonized to a considerably greater extent in susceptible P2 neonates than in corresponding tissues from infection-resistant 9-day-old rat pups; the bacteria appeared to damage and penetrate the nonkeratinized esophageal epithelium of infection-susceptible P2 animals, suggesting the esophagus represents a portal of entry for E. coli K1 into the systemic circulation. Thus, multimodality imaging of experimental systemic infections in real time indicates complex dynamic patterns of colonization and dissemination that provide new insights into the E. coli K1 infection of the neonatal rat.

Quorum Sensing Peptides Selectively Penetrate the Blood-Brain Barrier

Bacteria communicate with each other by the use of signaling molecules, a process called 'quorum sensing'. One group of quorum sensing molecules includes the oligopeptides, which are mainly produced by Gram-positive bacteria. Recently, these quorum sensing peptides were found to biologically influence mammalian cells, promoting i.a. metastasis of cancer cells. Moreover, it was found that bacteria can influence different central nervous system related disorders as well, e.g. anxiety, depression and autism. Research currently focuses on the role of bacterial metabolites in this bacteria-brain interaction, with the role of the quorum sensing peptides not yet known. Here, three chemically diverse quorum sensing peptides were investigated for their brain influx (multiple time regression technique) and efflux properties in an in vivo mouse model (ICR-CD-1) to determine blood-brain transfer properties: PhrCACET1 demonstrated comparatively a very high initial influx into the mouse brain (Kin = 20.87 μl/(g×min)), while brain penetrabilities of BIP-2 and PhrANTH2 were found to be low (Kin = 2.68 μl/(g×min)) and very low (Kin = 0.18 μl/(g×min)), respectively. All three quorum sensing peptides were metabolically stable in plasma (in vitro) during the experimental time frame and no significant brain efflux was observed. Initial tissue distribution data showed remarkably high liver accumulation of BIP-2 as well. Our results thus support the potential role of some quorum sensing peptides in different neurological disorders, thereby enlarging our knowledge about the microbiome-brain axis.

Endocytosis of Nanomedicines: The Case of Glycopeptide Engineered PLGA Nanoparticles

The success of nanomedicine as a new strategy for drug delivery and targeting prompted the interest in developing approaches toward basic and clinical neuroscience. Despite enormous advances on brain research, central nervous system (CNS) disorders remain the world's leading cause of disability, in part due to the inability of the majority of drugs to reach the brain parenchyma. Many attempts to use nanomedicines as CNS drug delivery systems (DDS) were made; among the various non-invasive approaches, nanoparticulate carriers and, particularly, polymeric nanoparticles (NPs) seem to be the most interesting strategies. In particular, the ability of poly-lactide-co-glycolide NPs (PLGA-NPs) specifically engineered with a glycopeptide (g7), conferring to NPs' ability to cross the blood brain barrier (BBB) in rodents at a concentration of up to 10% of the injected dose, was demonstrated in previous studies using different routes of administrations. Most of the evidence on NP uptake mechanisms reported in the literature about intracellular pathways and processes of cell entry is based on in vitro studies. Therefore, beside the particular attention devoted to increasing the knowledge of the rate of in vivo BBB crossing of nanocarriers, the subsequent exocytosis in the brain compartments, their fate and trafficking in the brain surely represent major topics in this field.

Non-invasive model of neuropathogenic Escherichia coli infection in the neonatal rat

Investigation of the interactions between animal host and bacterial pathogen is only meaningful if the infection model employed replicates the principal features of the natural infection. This protocol describes procedures for the establishment and evaluation of systemic infection due to neuropathogenic Escherichia coli K1 in the neonatal rat. Colonization of the gastrointestinal tract leads to dissemination of the pathogen along the gut-lymph-blood-brain course of infection and the model displays strong age dependency. A strain of E. coli O18:K1 with enhanced virulence for the neonatal rat produces exceptionally high rates of colonization, translocation to the blood compartment and invasion of the meninges following transit through the choroid plexus. As in the human host, penetration of the central nervous system is accompanied by local inflammation and an invariably lethal outcome. The model is of proven utility for studies of the mechanism of pathogenesis, for evaluation of therapeutic interventions and for assessment of bacterial virulence.

Role of epidermal growth factor receptor signaling in the interaction of Neisseria meningitidis with endothelial cells

Neisseria meningitidis, the causative agent of meningitis and septicemia, attaches to and invades various cell types. Both steps induce and/or require tyrosine phosphorylation of host cell proteins. Here, we used a phospho array platform to identify active receptor tyrosine kinases (RTKs) and key signaling nodes in N. meningitidis-infected brain endothelial cells to decipher RTK-dependent signaling pathways necessary for bacterial uptake. We detected several activated RTKs, including the ErbB family receptors epidermal growth factor receptor (EGFR), ErbB2, and ErbB4. We found that pharmacological inhibition and genetic ablation of ErbB receptor tyrosine phosphorylation and expression resulted in decreased bacterial uptake and heterologous expression of EGFR, ErbB2, or ErbB4 in Chinese ovary hamster (CHO-K1) cells, which do not express of EGFR and ErbB4; the decrease caused a significant increase in meningococcal invasion. Activation of EGFR and ErbB4 was mediated by transactivation via the common ligand HB-EGF (heparin-binding EGF-like ligand), which was significantly elevated in infected cell culture supernatants. We furthermore determined that N. meningitidis induced phosphorylation of EGFR at Tyr845 independent of ligand binding, which required c-Src activation and was involved in mediating uptake of N. meningitidis into eukaryotic cells. Increased uptake was repressed by expression of EGFR Y845F, which harbored a point mutation in the kinase domain. In addition, activation of ErbB4 at its autophosphorylation site, Tyr1284, and phosphorylation of ErbB2 Thr686 were observed. Altogether, our results provide evidence that EGFR, ErbB2, and ErbB4 are activated in response to N. meningitidis infection and shed new light on the role of ErbB signaling in meningococcal infection biology.

A combined mass spectrometry strategy for complete posttranslational modification mapping of Neisseria meningitidis major pilin

Herein, we report a new approach, based on the combination of mass profiling and tandem mass spectrometry, to address the issue of localising all post-translational modifications (PTMs) on the major pilin protein PiIE expressed by the pathogenic Neisseria species. PilE is the main component of type IV pili; filamentous organelles expressed at the surface of many bacterial pathogens and important virulence factors. Previous reports have shown that PilE can harbour various combinations of PTMs and have established strong links between PTM and pathogenesis. Complete PTM mapping of proteins involved in bacterial infection is therefore highly desirable. The methodology we propose here allowed us to fully characterise the PilE proteoforms of Neisseria meningitidis strain 8013, definitively identifying all PTMs present on all proteoforms and localising their position on the protein backbone. These modifications include a processed and methylated N-terminus, disulfide bridge, glycosylation and glycerophosphorylation at two different sites. A key element of our approach is high resolution, intact mass measurement of the proteoforms, a piece of information completely lacking in all classical bottom-up proteomics strategies used for PTM analysis and without which it is difficult to ensure complete PTM mapping.

Altered innate defenses in the neonatal gastrointestinal tract in response to colonization by neuropathogenic Escherichia coli

Two-day-old (P2), but not 9-day-old (P9), rat pups are susceptible to systemic infection following gastrointestinal colonization by Escherichia coli K1. Age dependency reflects the capacity of colonizing K1 to translocate from gastrointestinal (GI) tract to blood. A complex GI microbiota developed by P2, showed little variation over P2 to P9, and did not prevent stable K1 colonization. Substantial developmental expression was observed over P2 to P9, including upregulation of genes encoding components of the small intestinal (α-defensins Defa24 and Defa-rs1) and colonic (trefoil factor Tff2) mucus barrier. K1 colonization modulated expression of these peptides: developmental expression of Tff2 was dysregulated in P2 tissues and was accompanied by a decrease in mucin Muc2. Conversely, α-defensin genes were upregulated in P9 tissues. We propose that incomplete development of the mucus barrier during early neonatal life and the capacity of colonizing K1 to interfere with mucus barrier maturation provide opportunities for neuropathogen translocation into the bloodstream.

Analysis of the SDS-PAGE patterns of outer membrane proteins from Escherichia coli strains that have lost the ability to form K1 antigen and varied in the susceptibility to normal human serum

We used SDS-polyacrylamide gel electrophoresis to investigate the outer membrane proteins (OMPs) band composition of 19 Escherichia coli K1 strains that have spontaneously lost the ability to form K1 polysaccharide capsule (E. coli K1-) and demonstrated different degrees of susceptibility to the bactericidal action of normal human serum. Presented results showed that there were differences between E. coli K1- strains in OMPs expressing capacity. The analysis performed on OMPs has not revealed a direct association between the different OMPs band composition and the susceptibility of these strains to the serum.

Can nutritional modulation of maternal intestinal microbiota influence the development of the infant gastrointestinal tract?

The gastrointestinal microbiota plays an important role in maintaining host health by preventing the colonization of pathogens, fermenting dietary compounds, and maintaining normal mucosal immunity. Particularly in early life, the composition of the microbiota profoundly influences the development and maturation of the gastrointestinal tract (GIT) mucosa, which may affect health in later life. Therefore, strategies to manipulate the microbiota during infancy may prevent the development of some diseases later in adult life. Earlier research suggested that term fetuses are sterile and that the initial bacterial colonization of the newborn GIT occurs only after the baby transits through the birth canal. However, recent studies have demonstrated that the colonization and/or contact of the fetus with the maternal GIT microbiota may start in utero. After vaginal birth, the colonization of the neonate GIT continues through contact with maternal feces and vaginal bacteria, leading to a relatively simple microbial community that is influenced by feeding type (breast vs. formula feeding). Maternal GIT microbiota, vaginal microbiota, and breast milk composition are influenced by maternal diet. Alterations of the maternal GIT microbiota composition via supplementation with probiotics and prebiotics have been shown; however, transfer of these benefits to the offspring remains to be demonstrated. This review focuses on the influence of maternal GIT microbiota during the pre- and postpartum periods on the colonization of the infant GIT. In particular, it examines the manipulation of the maternal GIT microbiota composition through the use of probiotics and/or prebiotics and subsequent consequences for the health of the offspring.

Human pathogens utilize host extracellular matrix proteins laminin and collagen for adhesion and invasion of the host

Laminin (Ln) and collagen are multifunctional glycoproteins that play an important role in cellular morphogenesis, cell signalling, tissue repair and cell migration. These proteins are ubiquitously present in tissues as a part of the basement membrane (BM), constitute a protective layer around blood capillaries and are included in the extracellular matrix (ECM). As a component of BMs, both Lns and collagen(s), thus function as major mechanical containment molecules that protect tissues from pathogens. Invasive pathogens breach the basal lamina and degrade ECM proteins of interstitial spaces and connective tissues using various ECM-degrading proteases or surface-bound plasminogen and matrix metalloproteinases recruited from the host. Most pathogens associated with the respiratory, gastrointestinal, or urogenital tracts, as well as with the central nervous system or the skin, have the capacity to bind and degrade Lns and collagen(s) in order to adhere to and invade host tissues. In this review, we focus on the adaptability of various pathogens to utilize these ECM proteins as enhancers for adhesion to host tissues or as a targets for degradation in order to breach the cellular barriers. The major pathogens discussed are Streptococcus, Staphylococcus, Pseudomonas, Salmonella, Yersinia, Treponema, Mycobacterium, Clostridium, Listeria, Porphyromonas and Haemophilus; Candida, Aspergillus, Pneumocystis, Cryptococcus and Coccidioides; Acanthamoeba, Trypanosoma and Trichomonas; retrovirus and papilloma virus.

Blood-brain barrier and retroviral infections

Homeostasis in the central nervous system (CNS) is maintained by active interfaces between the bloodstream and the brain parenchyma. The blood-brain barrier (BBB) constitutes a selective filter for exchange of water, solutes, nutrients, and controls toxic compounds or pathogens entry. Some parasites, bacteria, and viruses have however developed various CNS invasion strategies, and can bypass the brain barriers. Concerning viruses, these strategies include transport along neural pathways, transcytosis, infection of the brain endothelial cells, breaching of the BBB, and passage of infected-leukocytes. Moreover, neurotropic viruses can alter BBB functions, thus compromising CNS homeostasis. Retroviruses have been associated to human neurological diseases: HIV (human immunodeficiency virus 1) can induce HIV-associated dementia, and HTLV-1 (human T lymphotropic virus 1) is the etiological factor of tropical spastic paraparesis/HTLV-1 associated myelopathy (TSP/HAM). The present review focuses on how the different retroviruses interact with this structure, bypass it and alter its functions.

Mechanism of meningeal invasion by Neisseria meningitidis

The blood-cerebrospinal fluid barrier physiologically protects the meningeal spaces from blood-borne bacterial pathogens, due to the existence of specialized junctional interendothelial complexes. Few bacterial pathogens are able to reach the subarachnoidal space and among those, Neisseria meningitidis is the one that achieves this task the most constantly when present in the bloodstream. Meningeal invasion is a consequence of a tight interaction of meningococci with brain endothelial cells. This interaction, mediated by the type IV pili, is responsible for the formation of microcolonies on the apical surface of the cells. This interaction is followed by the activation of signaling pathways in the host cells leading to the formation of endothelial docking structures resembling those elicited by the interaction of leukocytes with endothelial cells during extravasation. The consequence of these bacterial-induced signaling events is the recruitment of intercellular junction components in the docking structure and the subsequent opening of the intercellular junctions.