Bacteria hijack a meningeal neuroimmune axis to facilitate brain invasion.

The meninges are densely innervated by nociceptive sensory neurons that mediate pain and headache1,2. Bacterial meningitis causes life-threatening infections of the meninges and central nervous system, affecting more than 2.5 million people a year3-5. How pain and neuroimmune interactions impact meningeal antibacterial host defences are unclear. Here we show that Nav1.8+ nociceptors signal to immune cells in the meninges through the neuropeptide calcitonin gene-related peptide (CGRP) during infection. This neuroimmune axis inhibits host defences and exacerbates bacterial meningitis. Nociceptor neuron ablation reduced meningeal and brain invasion by two bacterial pathogens: Streptococcus pneumoniae and Streptococcus agalactiae. S. pneumoniae activated nociceptors through its pore-forming toxin pneumolysin to release CGRP from nerve terminals. CGRP acted through receptor activity modifying protein 1 (RAMP1) on meningeal macrophages to polarize their transcriptional responses, suppressing macrophage chemokine expression, neutrophil recruitment and dural antimicrobial defences. Macrophage-specific RAMP1 deficiency or pharmacological blockade of RAMP1 enhanced immune responses and bacterial clearance in the meninges and brain. Therefore, bacteria hijack CGRP-RAMP1 signalling in meningeal macrophages to facilitate brain invasion. Targeting this neuroimmune axis in the meninges can enhance host defences and potentially produce treatments for bacterial meningitis.

Streptococcus pneumoniae Rapidly Translocate from the Nasopharynx through the Cribriform Plate to Invade the Outer Meninges.

The entry routes and translocation mechanisms of microorganisms or particulate materials into the central nervous system remain obscure We report here that Streptococcus pneumoniae (pneumococcus), or polystyrene microspheres of similar size, appear in the meninges of the dorsal cortex of mice within minutes of inhaled delivery. Recovery of viable bacteria from dissected tissue and fluorescence microscopy show that up to at least 72 h, pneumococci and microspheres were predominantly found in the outer of the two meninges: the pachymeninx. No pneumococci were found in blood or cerebrospinal fluid. Intravital imaging through the skull, aligned with flow cytometry showed recruitment and activation of LysM+ cells in the dorsal pachymeninx at 5 and 10 hours following intranasal infection. Imaging of the cribriform plate suggested that both pneumococci and microspheres entered through the foramina via an inward flow of fluid connecting the nose to the pachymeninx. Our findings bring new insight into the varied mechanisms of pneumococcal invasion of the central nervous system, but they are also pertinent to the delivery of drugs to the brain and the entry of airborne particulate matter into the cranium. IMPORTANCE Using two-photon imaging, we show that pneumococci translocate from the nasopharynx to the dorsal meninges of a mouse in the absence of any bacteria found in blood or cerebrospinal fluid. Strikingly, this takes place within minutes of inhaled delivery of pneumococci, suggesting the existence of an inward flow of fluid connecting the nasopharynx to the meninges, rather than a receptor-mediated mechanism. We also show that this process is size dependent, as microspheres of the same size as pneumococci can translocate along the same pathway, while larger size microspheres cannot. Furthermore, we describe the host response to invasion of the outer meninges. Our study provides a completely new insight into the key initial events that occur during the translocation of pneumococci directly from the nasal cavity to the meninges, with relevance to the development of intranasal drug delivery systems and the investigations of brain damage caused by inhaled air pollutants.

The gut-meningeal immune axis: Priming brain defense against the most likely invaders.

The gastrointestinal tract contains trillions of microorganisms that exist symbiotically with the host due to a tolerant, regulatory cell-rich intestinal immune system. However, this intimate relationship with the microbiome inevitably comes with risks, with intestinal organisms being the most common cause of bacteremia. The vasculature of the brain-lining meninges contains fenestrated endothelium, conferring vulnerability to invasion by circulating microbes. We propose that this has evolutionarily led to close links between gut and meningeal immunity, to prime the central nervous system defense against the most likely invaders. This paradigm is exemplified by the dural venous sinus IgA defense system, where the antibody repertoire mirrors that of the gut.

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.

Preclinical models to optimize treatment of tuberculous meningitis - A systematic review.

Tuberculous meningitis (TBM) is the most devastating form of TB, resulting in death or neurological disability in up to 50% of patients affected. Treatment is similar to that of pulmonary TB, despite poor cerebrospinal fluid (CSF) penetration of the cornerstone anti-TB drug rifampicin. Considering TBM pathology, it is critical that optimal drug concentrations are reached in the meninges, brain and/or the surrounding CSF. These type of data are difficult to collect in TBM patients. This review aims to identify and describe a preclinical model representative for human TBM which can provide the indispensable data needed for future pharmacological characterization and prioritization of new TBM regimens in the clinical setting. We reviewed existing literature on treatment of TBM in preclinical models: only eight articles, all animal studies, could be identified. None of the animal models completely recapitulated human disease and in most of the animal studies key pharmacokinetic data were missing, making the comparison with human exposure and CNS distribution, and the study of pharmacokinetic-pharmacodynamic relationships impossible. Another 18 articles were identified using other bacteria to induce meningitis with treatment including anti-TB drugs (predominantly rifampicin, moxifloxacin and levofloxacin). Of these articles the pharmacokinetics, i.e. plasma exposure and CSF:plasma ratios, of TB drugs in meningitis could be evaluated. Exposures (except for levofloxacin) agreed with human exposures and also most CSF:plasma ratios agreed with ratios in humans. Considering the lack of an ideal preclinical pharmacological TBM model, we suggest a combination of 1. basic physicochemical drug data combined with 2. in vitro pharmacokinetic and efficacy data, 3. an animal model with adequate pharmacokinetic sampling, microdialysis or imaging of drug distribution, all as a base for 4. physiologically based pharmacokinetic (PBPK) modelling to predict response to TB drugs in treatment of TBM.

An atlas overview of characteristic features of tuberculosis that may be encountered at autopsy.

Tuberculosis (TB) is a bacterial infection caused by Mycobacterium tuberculosis. Although primarily a disease of the respiratory system it may be found in any organ or tissue. Global population movements and the emergence of resistant strains are contributing to increasing numbers of cases in certain populations. Subtlety of symptoms and signs, chronicity of disease and failure to seek medical assistance may result in the diagnosis only being made at the time of autopsy. For this reason forensic pathologists need to understand the protean manifestations of the disease and the variable mechanisms by which TB may cause death. This atlas overview provides descriptions of the pathological manifestations of TB in a variety of organs with accompanying illustrations. It serves as a summary of conditions that should be checked for at autopsy in suspected or confirmed cases.

Streptococcus pneumoniae serotypes with meningeal tropism in cases of invasive pneumococcal disease. Community of Madrid, 2007-2018. / Serotipos de Streptococcus pneumoniae con tropismo meníngeo en casos de enfermedad neumocócica invasora. Comunidad de Madrid, 2007-2018.

INTRODUCTION: To describe the distribution of Streptococcus pneumoniae serotypes isolated in cerebrospinal fluid (CSF) between 2007-2018 in the Community of Madrid (CM) and to identify those with higher meningeal tropism. METHODS: Strains isolated from invasive pneumococcal disease were sent to the Regional Laboratory of Public Health by Microbiology laboratories of public and private hospitals of the CM. The frequency of serotypes from CSF was compared with that observed in other samples. RESULTS: A total of 6,115 strains were processed and 5% (n=304) were isolated from CSF. Seven serotypes (11A, 19F, 23B, 10A, 24F, 23A and 35F) showed a frequency significantly higher in CSF than in other usually sterile samples. Serotypes 24F, 11A and 23B showed high penicillin-resistance. CONCLUSION: The frequency and resistance of certain pneumococcal serotypes with high meningeal tropism could compromise the treatment of central nervous system infections.

High-resolution analysis of the pneumococcal transcriptome under a wide range of infection-relevant conditions.

Streptococcus pneumoniae is an opportunistic human pathogen that typically colonizes the nasopharyngeal passage and causes lethal disease in other host niches, such as the lung or the meninges. The expression and regulation of pneumococcal genes at different life-cycle stages, such as commensal or pathogenic, are not entirely understood. To chart the transcriptional responses of S. pneumoniae, we used RNA-seq to quantify the relative abundance of the transcriptome under 22 different infection-relevant conditions. The data demonstrated a high level of dynamic expression and, strikingly, all annotated pneumococcal genomic features were expressed in at least one of the studied conditions. By computing the correlation values of every pair of genes across all studied conditions, we created a co-expression matrix that provides valuable information on both operon structure and regulatory processes. The co-expression data are highly consistent with well-characterized operons and regulons, such as the PyrR, ComE and ComX regulons, and have allowed us to identify a new member of the competence regulon. Lastly, we created an interactive data center named PneumoExpress (https://veeninglab.com/pneumoexpress) that enables users to access the expression data as well as the co-expression matrix in an intuitive and efficient manner, providing a valuable resource to the pneumococcal research community.

Borrelia burgdorferi adhere to blood vessels in the dura mater and are associated with increased meningeal T cells during murine disseminated borreliosis.

Borrelia burgdorferi, the causative agent of Lyme disease, is a vector-borne bacterial infection that is transmitted through the bite of an infected tick. If not treated with antibiotics during the early stages of infection, disseminated infection can spread to the central nervous system (CNS). In non-human primates (NHPs) it has been demonstrated that the leptomeninges are among the tissues colonized by B. burgdorferi spirochetes. Although the NHP model parallels aspects of human borreliosis, a small rodent model would be ideal to study the trafficking of spirochetes and immune cells into the CNS. Here we show that during early and late disseminated infection, B. burgdorferi infects the meninges of intradermally infected mice, and is associated with concurrent increases in meningeal T cells. We found that the dura mater was consistently culture positive for spirochetes in transcardially perfused mice, independent of the strain of B. burgdorferi used. Within the dura mater, spirochetes were preferentially located in vascular regions, but were also present in perivascular, and extravascular regions, as late as 75 days post-infection. At the same end-point, we observed significant increases in the number of CD3+ T cells within the pia and dura mater, as compared to controls. Flow cytometric analysis of leukocytes isolated from the dura mater revealed that CD3+ cell populations were comprised of both CD4 and CD8 T cells. Overall, our data demonstrate that similarly to infection in peripheral tissues, spirochetes adhere to the dura mater during disseminated infection, and are associated with increases in the number of meningeal T cells. Collectively, our results demonstrate that there are aspects of B. burgdorferi meningeal infection that can be modelled in laboratory mice, suggesting that mice may be useful for elucidating mechanisms of meningeal pathogenesis by B. burgdorferi.

Uncommon Pathogen Bacillus Cereus Causing Subdural Empyema in a Child.

BACKGROUND: Subdural empyema (SDE) in children is a severe intracranial infection. Many pathogens can cause SDE. CASE DETAILS: In this articlewe present a 15-month old Indonesian boy diagnosed as SDE based on the clinical symptoms and neuroimaging. A complete blood count showed white blood cell count of 13.800/mm3 and the CRP level was 8.3 mg/L. Craniotomy following burr hole drainage procedure was performed to decrease intracranial pressure. The liquor culture indicated Bacillus cereus. A meropenem injection and metronidazole infusion were administered appropriately with antibiotic sensitivity for several weeks. Immediate initiation of appropriate antibiotic therapy related to an accelerated surgical drainage can improve the outcome. CONCLUSION: The combination of medication and surgery treatment for Bacillus cereus in SDE resulted in a good response, leaving neurological sequelae.

The meninges as barriers and facilitators for the movement of fluid, cells and pathogens related to the rodent and human CNS.

Meninges that surround the CNS consist of an outer fibrous sheet of dura mater (pachymeninx) that is also the inner periosteum of the skull. Underlying the dura are the arachnoid and pia mater (leptomeninges) that form the boundaries of the subarachnoid space. In this review we (1) examine the development of leptomeninges and their role as barriers and facilitators in the foetal CNS. There are two separate CSF systems during early foetal life, inner CSF in the ventricles and outer CSF in the subarachnoid space. As the foramina of Magendi and Luschka develop, one continuous CSF system evolves. Due to the lack of arachnoid granulations during foetal life, it is most likely that CSF is eliminated by lymphatic drainage pathways passing through the cribriform plate and nasal submucosa. (2) We then review the fine structure of the adult human and rodent leptomeninges to establish their roles as barriers and facilitators for the movement of fluid, cells and pathogens. Leptomeningeal cells line CSF spaces, including arachnoid granulations and lymphatic drainage pathways, and separate elements of extracellular matrix from the CSF. The leptomeningeal lining facilitates the traffic of inflammatory cells within CSF but also allows attachment of bacteria such as Neisseria meningitidis and of tumour cells as CSF metastases. Single layers of leptomeningeal cells extend into the brain closely associated with the walls of arteries so that there are no perivascular spaces around arteries in the cerebral cortex. Perivascular spaces surrounding arteries in the white matter and basal ganglia relate to their two encompassing layers of leptomeninges. (3) Finally we examine the roles of ligands expressed by leptomeningeal cells for the attachment of inflammatory cells, bacteria and tumour cells as understanding these roles may aid the design of therapeutic strategies to manage developmental, autoimmune, infectious and neoplastic diseases relating to the CSF, the leptomeninges and the associated CNS.

Nasopharyngeal glial heterotopia with delayed postoperative meningitis.

A male infant, who underwent radical resection of a large glial heterotopia at the nasopharynx at 8 days, developed delayed postoperative bacterial meningitis at 9 months. Neuroradiological examination clearly demonstrated that meningitis had occurred because of the intracranial and extracranial connections, which were scarcely seen in the perioperative period. A transsphenoidal extension of hypothalamic hamartoma is possible because the connection started from the right optic nerve, running through the transsphenoidal canal in the sphenoid bone and terminating at the recurrent mass in the nasopharyngeal region.

Pharmacokinetics and cerebrospinal fluid penetration of norvancomycin in Chinese adult patients.

Norvancomycin is an antibiotic that has been approved for the treatment of infections caused by antibiotic-resistant Gram-positive bacteria and has been used in China for more than a decade. However, the cerebrospinal fluid (CSF) penetration of norvancomycin has not been evaluated. The aims of the study were (i) to investigate the pharmacokinetics and CSF penetration of norvancomycin in meningitis and non-meningitis patients and (ii) to recommend favourable dosing regimens in meningitis patients. Twenty adult patients (ten with meningitis and ten without meningitis) requiring norvancomycin treatment were enrolled. All patients received a norvancomycin regimen of 800 mg every 12 h. Blood and CSF samples were consecutively collected up to 12 h after the end of the fourth 60-min infusion. Norvancomycin concentrations both in serum and CSF were measured using a high-performance liquid chromatography (HPLC) assay. CSF penetration of norvancomycin was evaluated by calculating the CSF/serum ratio. Mean norvancomycin serum trough levels were 9.9 ± 1.44 µg/mL in patients with meningitis and 10.08 ± 1.12 µg/mL in patients without meningitis (P > 0.05). In addition, norvancomycin penetrated into the inflamed meninges, with mean CSF concentrations of 3.93-10.52 µg/mL and mean CSF/serum ratios of 0.18-0.43, both of which were significantly higher than in patients without meningitis (P <0.05). These results suggest that norvancomycin has higher CSF penetration in patients with meningitis compared with other groups and that norvancomycin is effective in treating patients with purulent meningitis at a comparably low dose.

A journey into the brain: insight into how bacterial pathogens cross blood-brain barriers.

The blood-brain barrier, which is one of the tightest barriers in the body, protects the brain from insults, such as infections. Indeed, only a few of the numerous blood-borne bacteria can cross the blood-brain barrier to cause meningitis. In this Review, we focus on invasive extracellular pathogens, such as Neisseria meningitidis, Streptococcus pneumoniae, group B Streptococcus and Escherichia coli, to review the obstacles that bacteria have to overcome in order to invade the meninges from the bloodstream, and the specific skills they have developed to bypass the blood-brain barrier. The medical importance of understanding how these barriers can be circumvented is underlined by the fact that we need to improve drug delivery into the brain.

Multicentric Cryptococcosis in a Congo African Grey Parrot ( Psittacus erithacus erithacus).

An approximately 10-year-old, female Congo African grey parrot ( Psittacus erithacus erithacus) developed progressive, unilateral exophthalmos and buphthalmos. Survey radiographs revealed a large, coelomic, soft tissue mass, which was confirmed on computed tomography scan. Aspirates of both the contents of the buphthalmic globe and coelomic mass were consistent with Cryptococcus species. Initial results were later confirmed with serum antigen latex agglutination and polymerase chain reaction testing, and the organism was then identified as Cryptococcus neoformans with DNA sequencing. During the course of 1 year, the bird was treated with combinations of oral terbinafine, fluconazole, and flucytosine, as well as intraocular amphotericin B. The coelomic mass dramatically decreased in size during the course of treatment, but the globe continued to enlarge. The bird died after exhibiting ataxia and seizures approximately 13 months after initial diagnosis, and necropsy confirmed colonization of the cerebrum and meninges with Cryptococcus. Cryptococcus remains a rare fungal disease of birds that is often refractory to treatment.

Cerebral hemorrhage due to tuberculosis meningitis: a rare case report and literature review.

Tuberculosis (TB) is a common disease to threaten human health. TB of the central nervous system (CNS) is rare but the most serious type of systemic TB because of its high mortality rate, serious neurological complications and sequelae. In this case report, we describe a woman who presented with walking instability, intracerebral hemorrhage and leptomeningeal enhancement due to tuberculosis meningitis. The patient had no significant medical history and the initial clinical symptoms were walking instability. On analysis, the cerebrospinal fluid was colorless and transparent, the pressure was more than 400 mm H2O, there was lymphocytic pleocytosis, increased protein, and decreased glucose levels present. No tuberculosis or other bacteria were detected. The patient's brain computed tomography image showed intra-cerebral hemorrhage (ICH) and contrast magnetic resonance imaging showed ICH in the right frontal lob, and leptomeningeal enhancement. CNS TB is rare but has a high mortality rate. As this disease has no unique characteristics at first presentation such as epidemiology and obvious clinical manifestation, a diagnosis of CNS TB remains difficult.

Interactions of Streptococcus suis serotype 2 with human meningeal cells and astrocytes.

BACKGROUND: Streptococcus suis serotype 2 is an important porcine pathogen and emerging zoonotic agent responsible for meningitis, of which different sequence types predominate worldwide. Though bacterial meningitis is defined as an exacerbated inflammation of the meninges, the underlying astrocytes of the glia limitans superficialis may also be implicated. However, the interactions between this pathogen and human meningeal cells or astrocytes remain unknown. Furthermore, the roles of well-described virulence factors (capsular polysaccharide, suilysin and cell wall modifications) in these interactions have yet to be studied. Consequently, the interactions between S. suis serotype 2 and human meningeal cells or astrocytes were evaluated for the first time in order to better understand their involvement during meningitis in humans. RESULTS: Streptococcus suis serotype 2 adhered to human meningeal cells and astrocytes; invasion of meningeal cells was rare however, whereas invasion of astrocytes was generally more frequent. Regardless of the interaction or cell type, differences were not observed between sequence types. Though the capsular polysaccharide modulated the adhesion to and invasion of meningeal cells and astrocytes, the suilysin and cell wall modifications only influenced astrocyte invasion. Surprising, S. suis serotype 2 induced little or no inflammatory response from both cell types, but this absence of inflammatory response was probably not due to S. suis-induced cell death. CONCLUSIONS: Though S. suis serotype 2 interacted with human meningeal cells and astrocytes, there was no correlation between sequence type and interaction. Consequently, the adhesion to and invasion of human meningeal cells and astrocytes are strain-specific characteristics. As such, the meningeal cells of the leptomeninges and the astrocytes of the glia limitans superficialis may not be directly implicated in the inflammatory response observed during meningitis in humans.

Comparative proteomics of cerebrospinal fluid reveals a predictive model for differential diagnosis of pneumococcal, meningococcal, and enteroviral meningitis, and novel putative therapeutic targets.

BACKGROUND: Meningitis is the inflammation of the meninges in response to infection or chemical agents. While aseptic meningitis, most frequently caused by enteroviruses, is usually benign with a self-limiting course, bacterial meningitis remains associated with high morbidity and mortality rates, despite advances in antimicrobial therapy and intensive care. Fast and accurate differential diagnosis is crucial for assertive choice of the appropriate therapeutic approach for each form of meningitis. METHODS: We used 2D-PAGE and mass spectrometry to identify the cerebrospinal fluid proteome specifically related to the host response to pneumococcal, meningococcal, and enteroviral meningitis. The disease-specific proteome signatures were inspected by pathway analysis. RESULTS: Unique cerebrospinal fluid proteome signatures were found to the three aetiological forms of meningitis investigated, and a qualitative predictive model with four protein markers was developed for the differential diagnosis of these diseases. Nevertheless, pathway analysis of the disease-specific proteomes unveiled that Kallikrein-kinin system may play a crucial role in the pathophysiological mechanisms leading to brain damage in bacterial meningitis. Proteins taking part in this cellular process are proposed as putative targets to novel adjunctive therapies. CONCLUSIONS: Comparative proteomics of cerebrospinal fluid disclosed candidate biomarkers, which were combined in a qualitative and sequential predictive model with potential to improve the differential diagnosis of pneumococcal, meningococcal and enteroviral meningitis. Moreover, we present the first evidence of the possible implication of Kallikrein-kinin system in the pathophysiology of bacterial meningitis.

Efficacy of Ceftaroline Fosamil against Escherichia coli and Klebsiella pneumoniae strains in a rabbit meningitis model.

In this study, the efficacy of ceftaroline fosamil was compared with that of cefepime in an experimental rabbit meningitis model against two Gram-negative strains (Escherichia coli QK-9 and Klebsiella pneumoniae 1173687). The penetration of ceftaroline into inflamed and uninflamed meninges was also investigated. Both regimens were bactericidal, but ceftaroline fosamil was significantly superior to cefepime against K. pneumoniae and E. coli in this experimental rabbit meningitis model (P < 0.0007 against K. pneumoniae and P < 0.0016 against E. coli). The penetration of ceftaroline was approximately 15% into inflamed meninges and approximately 3% into uninflamed meninges.

Haemophilus influenzae type f meningitis in a previously healthy boy.

Non-serotype b strains of Haemophilus influenzae are extremely rare causes of acute bacterial meningitis in immunocompetent individuals. We report a case of acute bacterial meningitis in a 14-year-old boy, who was previously healthy and had been immunised against H influenzae serotype b (Hib). The causative pathogen was identified as H influenzae serotype f (Hif), and was successfully treated with ceftriaxone. An immunological evaluation revealed transient low levels of immunoglobulins but no apparent immunodeficiency was found 2 years after the clinical insult.