Mechanisms of injury in bacterial meningitis

The clinical presentation of acute bacterial meningitis varies with age, sex and duration of illness

AIM

This Swedish study reviewed differences in clinical presentation and laboratory findings of acute bacterial meningitis in children aged one month to 17 years in Västerbotten County, Sweden.

METHODS

A register-based study was performed for the period 1986 to 2013 using the Västerbotten County Council's patient registration and laboratory records at the Department of Laboratory Medicine at Umeå University Hospital. The medical records were reviewed to extract data and confirm the diagnosis.

RESULTS

We found 103 cases of acute bacterial meningitis, and Haemophilus influenzae was the most common pathogen, causing 40.8% of all cases, followed by Streptococcus pneumoniae at 30.1% and Neisseria meningitidis at 9.7%. Significant differences in clinical presentation and laboratory findings were found. Younger children were more unwell than older ones and had more diffuse symptoms on admission. In addition, important sex-related differences were found that might explain the higher case fatality rates for boys than girls. For example, boys tended to have a higher disturbance in the blood-brain barrier, which is known to be a negative prognostic factor.

CONCLUSION

This study showed that clinical presentation for acute bacterial meningitis varied with age and sex and, to a lesser extent, on the duration of the illness.

Brain ventricular dimensions and relationship to outcome in adult patients with bacterial meningitis

Background

Experimental studies suggest that changes in brain ventricle size are key events in bacterial meningitis. This study investigated the relationship between ventricle size, clinical condition and risk of poor outcome in patients with bacterial meningitis.

Methods

Adult patients diagnosed with bacterial meningitis admitted to two departments of infectious diseases from 2003 through 2010 were identified. Clinical and biochemical data as well as cerebral computed tomographic images were collected. The size of the brain ventricles were presented as a Ventricle to Brain Ratio (VBR). Normal range of VBR was defined from an age matched control group. A multivariate analysis was performed to identify predictors of 30-day mortality.

Results

One hundred and seven patients were included. Eighty-one patients had a CT scan at the time of diagnosis. VBR was identified as an independent risk factor of 30-day mortality, Mortality Rate Ratio: 6.03 (95 % confidence interval: 1.61-22.64, p = 0.008) for highest versus lowest tertile. A VBR deviating more than 2 standard deviations from the normal range was associated with increased mortality.

Conclusions

Brain ventricles are commonly subject to marked changes in size as a consequence of meningitis. Increased brain ventricle size in the acute phase of bacterial meningitis was associated with increased mortality.

Electronic supplementary material

The online version of this article (doi:10.1186/s12879-015-1097-3) contains supplementary material, which is available to authorized users.

Microglia are crucial regulators of neuro-immunity during central nervous system tuberculosis

Mycobacterium tuberculosis (M. tuberculosis) infection of the central nervous system (CNS) is the most devastating manifestation of tuberculosis (TB), with both high mortality and morbidity. Although research has been fueled by the potential therapeutic target microglia offer against neurodegenerative inflammation, their part in TB infection of the CNS has not been fully evaluated nor elucidated. Yet, as both the preferential targets of M. tuberculosis and the immune-effector cells of the CNS, microglia are likely to be key determinants of disease severity and clinical outcomes. Following pathogen recognition, bacilli are internalized and capable of replicating within microglia. Cellular activation ensues, utilizing signaling molecules that may be neurotoxic. Central to initiating, orchestrating and modulating the tuberculous immune response is microglial secretion of cytokines and chemokines. However, the neurological environment is unique in that inflammatory signals, which appear to be damaging in the periphery, could be beneficial by governing neuronal survival, regeneration and differentiation. Furthermore, microglia are important in the recruitment of peripheral immune cells and central to defining the pro-inflammatory milieu of which neurotoxicity may result from many of the participating local or recruited cell types. Microglia are capable of both presenting antigen to infiltrating CD4(+) T-lymphocytes and inducing their differentiation-a possible correlate of protection against M. tuberculosis infection. Clarifying the nature of the immune effector molecules secreted by microglia, and the means by which other CNS-specific cell types govern microglial activation or modulate their responses is critical if improved diagnostic and therapeutic strategies are to be attained. Therefore, this review evaluates the diverse roles microglia play in the neuro-immunity to M. tuberculosis infection of the CNS.

Intrathecal application of the antimicrobial peptide CRAMP reduced mortality and neuroinflammation in an experimental model of pneumococcal meningitis

Antimicrobial peptides (AP) are important components of the innate immune system. Our previous work revealed a higher mortality rate and up-regulation of proinflammatory gene expression as well as glial cell activation in cathelicidin-related antimicrobial peptide (CRAMP)-deficient mice after bacterial meningitis. However, the influence of CRAMP application on the progression of inflammation and its impact on mortality after bacterial meningitis remains unknown. To assess the effects of continuous CRAMP exposure in the brain, C57BL/6 wildtype mice were given intracerebroventricular infusion of CRAMP to investigate the effects on mortality, glial cell activation and inflammation in a mouse model of pneumococcal meningitis using immunohistochemistry and realtime RT-PCR. Our results revealed a decrease of mortality after CRAMP infusion. The intrathecal CRAMP infusion after pneumococcal meningitis resulted in a decreased mRNA expression of pro-inflammatory cytokines, whereas the immune responses including the expression of pattern recognition receptors and chemokines were increased in bacterial meningitis. Taken together, the results support the important role of CRAMP as part of the innate immune response against pathogens in bacterial CNS infections. The APs may be a promising approach for the development of an adjuvant therapy for bacterial meningitis.

The antidepressant fluoxetine protects the hippocampus from brain damage in experimental pneumococcal meningitis

BACKGROUND

High mortality and morbidity rates are observed in patients with bacterial meningitis (BM) and urge for new adjuvant treatments in addition to standard antibiotic therapies. In BM the hippocampal dentate gyrus is injured by apoptosis while in cortical areas ischemic necrosis occurs. Experimental therapies aimed at reducing the inflammatory response and brain damage have successfully been evaluated in animal models of BM. Fluoxetine (FLX) is an anti-depressant of the selective serotonin reuptake inhibitors (SSRI) and was previously shown to be neuroprotective in vitro and in vivo. We therefore assessed the neuroprotective effect of FLX in experimental pneumococcal meningitis.

METHODS

Infant rats were infected intracisternally with live Streptococcus pneumoniae. Intraperitoneal treatment with FLX (10mgkg(-1)d(-1)) or an equal volume of NaCl was initiated 15min later. 18, 27, and 42h after infection, the animals were clinically (weight, clinical score, mortality) evaluated and subject to a cisternal puncture and inflammatory parameters (i.e., cyto-/chemokines, myeloperoxidase activity, matrix metalloproteinase concentrations) were measured in cerebrospinal fluid (CSF) samples. At 42h after infection, animals were sacrificed and the brains collected for histomorphometrical analysis of brain damage.

RESULTS

A significant lower number of animals treated with FLX showed relevant hippocampal apoptosis when compared to littermates (9/19 animals vs 18/23, P=0.038). A trend for less damage in cortical areas was observed in FLX-treated animals compared to controls (13/19 vs 13/23, P=ns). Clinical and inflammatory parameters were not affected by FLX treatment.

CONCLUSION

A significant neuroprotective effect of FLX on the hippocampus was observed in acute pneumococcal meningitis in infant rats.

Neuroinflammation induced by intracerebroventricular injection of microbial neuraminidase

In the present paper, we describe the facts that took place in the rat brain after a single injection of the enzyme neuraminidase from Clostridium perfringens into the right lateral ventricle. After injection, it diffused through the cerebrospinal fluid of the ipsilateral ventricle and the third ventricle, and about 400 μm into the periventricular brain parenchyma. The expression of ICAM1 in the endothelial cells of the periventricular vessels, IBA1 in microglia, and GFAP in astrocytes notably increased in the regions reached by the injected neuraminidase. The subependymal microglia and the ventricular macrophages begun to express IL1β and some appeared to cross the ependymal layer. After about 4 h of the injection, leukocytes migrated from large venules of the affected choroid plexus, the meninges and the local subependyma, and infiltrated the brain. The invading cells arrived orderly: first neutrophils, then macrophage-monocytes, and last CD8α-positive T-lymphocytes and B-lymphocytes. Leukocytes in the ventricles and the perivascular zones penetrated the brain parenchyma passing through the ependyma and the glia limitans. Thus, it is likely that a great part of the damage produced by microorganism invading the brain may be due to their neuraminidase content.

Evaluation of hypothalamic-pituitary function in children following acute bacterial meningitis

BACKGROUND

Previous studies in adults and case reports in children have shown increased frequency of hypothalamo-pituitary dysfunction after infectious diseases of the central nervous system. The aim of this study was to evaluate the function of hypothalamo-pituitary axis in children with a history of bacterial meningitis.

METHODS

Patients diagnosed with bacterial meningitis between April 2000 and June 2011 was included. Baseline and stimulated hormonal tests were performed as required for hormonal evaluations following a diagnosis of meningitis.

RESULTS

Pituitary function was assessed following a period of 8-135 months (mean 53 months) after bacterial meningitis. Thirty-seven cases (27 male, 15 pubertal) with mean age of 11.1 ± 4.4 years were included. Mean height SDS was 0.01 ± 1.07 and mean BMI SDS was 0.54 ± 1.15 all patients had a SDS above -2 SD. Baseline cortisol and low dose ACTH stimulation revealed normal adrenal functions in all patients. Gonadotropin deficiency was not detected in any of the pubertal cases. Four cases (10.8%) had low IGF1 and IGFBP3 z-scores (<-2 SD) according to age, sex and Tanner stage, but peak GH response in clonidin test was >10 ng/ml in three of them suggesting neurosecretary dysfunction of GH in these cases. The fourth case has died before the test. No one had TSH deficiency and diabetes insipidus, only one case had mild hyperprolactinemia.

CONCLUSIONS

Our findings suggest that hypothalamo-pituitary dysfunction is not as common in childhood as in adulthood. The most remarkable finding was neurosecretary dysfunction of GH in some cases.

Vitamin D deficiency decreases survival of bacterial meningoencephalitis in mice

Background

Meningoencephalitis caused by Escherichia coli is associated with high rates of mortality and risk of neurological sequelae in newborns and infants and in older or immunocompromised adults. A high prevalence of neurological disorders has been observed in geriatric populations at risk of hypovitaminosis D.

Methods

In vivo, we studied the effects of vitamin D3 on survival and the host’s immune response in experimental bacterial meningoencephalitis in mice after intracerebral E. coli infection. To produce different systemic vitamin D3 concentrations, mice received a low, standard, or high dietary vitamin D3 supplementation. Bacterial titers in blood, spleen, and brain homogenates were determined. Leukocyte infiltration was assessed by histological scores, and tissue cytokine or chemokine concentrations were measured.

Results

Mice fed a diet with low vitamin D3 concentration died earlier than control animals after intracerebral infection. Vitamin D deficiency did not inhibit leukocyte recruitment into the subarachnoid space and did not lead to an increased density of bacteria in blood, spleen, or brain homogenates. The release of proinflammatory interleukin (IL)-6 was decreased and the release of anti-inflammatory IL-10 was increased in mice fed a diet with high vitamin D3 supplementation.

Conclusion

Our observations suggest a detrimental role of vitamin D deficiency in bacterial central nervous system infections. Vitamin D may exert immune regulatory functions.

Inhibition of matrix metalloproteinases attenuates brain damage in experimental meningococcal meningitis

BACKGROUND

Approximately 7% of survivors from meningococcal meningitis (MM) suffer from neurological sequelae due to brain damage in the course of meningitis. The present study focuses on the role of matrix metalloproteinases (MMPs) in a novel mouse model of MM-induced brain damage.

METHODS

The model is based on intracisternal infection of BALB/c mice with a serogroup C Neisseria meningitidis strain. Mice were infected with meningococci and randomised for treatment with the MMP inhibitor batimastat (BB-94) or vehicle. Animal survival, brain injury and host-response biomarkers were assessed 48 h after meningococcal challenge.

RESULTS

Mice that received BB-94 presented significantly diminished MMP-9 levels (p < 0.01), intracerebral bleeding (p < 0.01), and blood-brain barrier (BBB) breakdown (p < 0.05) in comparison with untreated animals. In mice suffering from MM, the amount of MMP-9 measured by zymography significantly correlated with both intracerebral haemorrhage (p < 0.01) and BBB disruption (p < 0.05).

CONCLUSIONS

MMPs significantly contribute to brain damage associated with experimental MM. Inhibition of MMPs reduces intracranial complications in mice suffering from MM, representing a potential adjuvant strategy in MM post-infection sequelae.

A putative role for homocysteine in the pathophysiology of acute bacterial meningitis in children

Background

Acute bacterial meningitis frequently causes cortical and hippocampal neuron loss leading to permanent neurological sequelae. Neuron death in acute bacterial meningitis involves the excessive activation of NMDA receptors and p53-mediated apoptosis, and the latter is triggered by the depletion of NAD + and ATP cellular stores by the DNA repair enzyme poly(ADP-ribose) polymerase. This enzyme is activated during acute bacterial meningitis in response to DNA damage induced, on its turn, by reactive oxygen and nitrogen species. An excess of homocysteine can also induce this cascade of events in hippocampal neurons.

The present work aimed at investigating the possible involvement of homocysteine in the pathophysiology of meningitis by comparing its concentrations in cerebrospinal fluid (CSF) samples from children with viral or acute bacterial meningitis, and control individuals.

Methods

Homocysteine and cysteine concentrations were assessed by high-performance liquid chromatography in CSF samples from nine patients with acute bacterial meningitis, 13 patients with viral meningitis and 18 controls (median age: 4 years-old; range: <1 to 13) collected by lumbar puncture at admission at the Children's Hospital Joao Paulo II - FHEMIG, from January 2010 to November 2011.

Results

We found that homocysteine accumulates up to neurotoxic levels within the central nervous system of patients with acute bacterial meningitis, but not in those with viral meningitis or control individuals. No correlation was found between homocysteine and cysteine concentrations and the cerebrospinal fluid standard cytochemical parameters.

Conclusions

Our results suggest that HCY is produced intrathecally in response to acute bacterial meningitis and accumulates within the central nervous system reaching potentially neurotoxic levels. This is the first work to propose a role for HCY in the pathophysiology of brain damage associated with acute bacterial meningitis.

Lymphocytes modulate innate immune responses and neuronal damage in experimental meningitis

In bacterial meningitis, excessive immune responses carry significant potential for damage to brain tissue even after successful antibiotic therapy. Bacterial meningitis is regarded primarily as the domain of innate immunity, and the role of lymphocytes remains unclear. We studied the contribution of lymphocytes to acute inflammation and neurodegeneration in experimental Toll-like receptor 2-driven meningitis, comparing wild-type mice with RAG-1-deficient mice that have no mature T and B lymphocytes. At 24 h after intrathecal challenge with the synthetic bacterial lipopeptide Pam(3)CysSK(4), RAG-1-deficient mice displayed more pronounced clinical impairment and an increased concentration of neutrophils, reduced expression of interleukin-10 (IL-10) mRNA, and increased expression of CXCL1 mRNA in the cerebrospinal fluid. Conversely, neuronal loss in the dentate gyrus was reduced in RAG-1-deficient mice, and expression of IL-10, transforming growth factor β and CCL2 mRNA by microglia was increased compared to wild-type mice. Adoptive transfer of wild-type lymphocytes reversed the enhanced meningeal inflammation and functional impairment observed in RAG-1-deficient mice. Our findings suggest compartment-specific effects of lymphocytes during acute bacterial meningitis, including attenuation of meningeal inflammation and shifting of microglial activation toward a more neurotoxic phenotype.

Treatment strategies for central nervous system infections: an update

INTRODUCTION

Central nervous system infection continues to be an important cause of mortality and morbidity worldwide. Our incomplete knowledge on the pathogenesis of how meningitis-causing pathogens cause CNS infection and emergence of antimicrobial resistance has contributed to the mortality and morbidity. An early empiric antibiotic treatment is critical for the management of patients with bacterial meningitis, but early recognition of bacterial meningitis continues to be a challenge.

AREAS COVERED

This review gives an overview on current therapeutic strategies for CNS infection with a focus on recent literature since 2010 on bacterial meningitis. Bacterial meningitis is a medical emergency, requiring early recognition and treatment. The selection of appropriate empiric antimicrobial regimen, after incorporating the epidemiology of bacterial meningitis, impact of vaccination, emergence of antimicrobial-resistant bacteria, role of adjunctive therapy and the current knowledge on the pathogenesis of meningitis and associated neuronal injury are covered.

EXPERT OPINION

Prompt treatment of bacterial meningitis with an appropriate antibiotic is essential. Optimal antimicrobial treatment of bacterial meningitis requires bactericidal agents able to penetrate the blood-brain barrier, with efficacy in cerebrospinal fluid. Emergence of CNS-infecting pathogens with resistance to conventional antibiotics has been increasingly recognized, but development of new antibiotics has been limited. More complete understanding of the microbial and host factors that are involved in the pathogenesis of bacterial meningitis and associated neurologic sequelae is likely to help in developing new strategies for the prevention and therapy of bacterial meningitis.

Pathogens penetrating the central nervous system: infection pathways and the cellular and molecular mechanisms of invasion

The brain is well protected against microbial invasion by cellular barriers, such as the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB). In addition, cells within the central nervous system (CNS) are capable of producing an immune response against invading pathogens. Nonetheless, a range of pathogenic microbes make their way to the CNS, and the resulting infections can cause significant morbidity and mortality. Bacteria, amoebae, fungi, and viruses are capable of CNS invasion, with the latter using axonal transport as a common route of infection. In this review, we compare the mechanisms by which bacterial pathogens reach the CNS and infect the brain. In particular, we focus on recent data regarding mechanisms of bacterial translocation from the nasal mucosa to the brain, which represents a little explored pathway of bacterial invasion but has been proposed as being particularly important in explaining how infection with Burkholderia pseudomallei can result in melioidosis encephalomyelitis.

Neisseria meningitidis elicits a pro-inflammatory response involving IκBζ in a human blood-cerebrospinal fluid barrier model

BACKGROUND

The human-specific, Gram-negative bacterium Neisseria meningitidis (Nm) is a leading cause of bacterial meningitis worldwide. The blood-cerebrospinal fluid barrier (BCSFB), which is constituted by the epithelial cells of the choroid plexus (CP), has been suggested as one of the potential entry sites of Nm into the CSF and can contribute to the inflammatory response during infectious diseases of the brain. Toll-like receptors (TLRs) are involved in mediating signal transduction caused by the pathogens.

METHODS

Using a recently established in vitro model of the human BCSFB based on human malignant CP papilloma (HIBCPP) cells we investigated the cellular response of HIBCPP cells challenged with the meningitis-causing Nm strain, MC58, employing transcriptome and RT-PCR analysis, cytokine bead array, and enzyme-linked immunosorbent assay (ELISA). In comparison, we analyzed the answer to the closely related unencapsulated carrier isolate Nm α14. The presence of TLRs in HIBCPP and their role during signal transduction caused by Nm was studied by RT-PCR and the use of specific agonists and mutant bacteria.

RESULTS

We observed a stronger transcriptional response after infection with strain MC58, in particular with its capsule-deficient mutant MC58siaD-, which correlated with bacterial invasion levels. Expression evaluation and Gene Set Enrichment Analysis pointed to a NFκB-mediated pro-inflammatory immune response involving up-regulation of the transcription factor IκBζ. Infected cells secreted significant levels of pro-inflammatory chemokines and cytokines, including, among others, IL8, CXCL1-3, and the IκBζ target gene product IL6. The expression profile of pattern recognition receptors in HIBCPP cells and the response to specific agonists indicates that TLR2/TLR6, rather than TLR4 or TLR2/TLR1, is involved in the cellular reaction following Nm infection.

CONCLUSIONS

Our data show that Nm can initiate a pro-inflammatory response in human CP epithelial cells probably involving TLR2/TLR6 signaling and the transcriptional regulator IκBζ.

Usefulness of interleukin 6 levels in the cerebrospinal fluid for the diagnosis of bacterial meningitis

PURPOSE

Interleukin 6 (IL-6) is a proinflammatory cytokine produced during infections. We hypothesized that IL-6 levels in the cerebrospinal fluid (CSF) would be elevated in bacterial meningitis and useful for diagnosing and predicting neurologic outcomes.

MATERIALS AND METHODS

For the differentiation of bacterial meningitis, serum and CSF samples were obtained from patients with an altered level of consciousness. Patients were classified into 3 groups: bacterial meningitis, nonbacterial central nervous system disease, and other site sepsis.

RESULTS

Of the 70 patients included in this study, there were 13 in the bacterial meningitis group, 21 in the nonbacterial central nervous system disease group, and 36 in the other site sepsis group. The CSF IL-6 level was significantly higher in the bacterial meningitis group than in the other 2 groups (P<.0001). Of the 5 CSF parameters assessed, CSF IL-6 level exhibited the largest area under the receiver operating characteristic curve (0.962), with a cut-off value of 644 pg/mL (sensitivity, 92.3%; specificity, 89.5%). To examine a potential association between a high CSF level and neurologic outcome, CSF IL-6 levels were divided into 4 quartiles, and each level was compared with the frequency of a good neurologic outcome. The frequency of a good neurologic outcome was significantly lower in the highest CSF IL-6 quartile than in the other 3 quartiles (odds ratio, 0.18; 95% confidence interval, 0.05-0.69; P=.013).

CONCLUSIONS

Measurement of the CSF IL-6 level is useful for diagnosing bacterial meningitis.

Matrix metalloproteinase inhibition lowers mortality and brain injury in experimental pneumococcal meningitis

Pneumococcal meningitis (PM) results in high mortality rates and long-lasting neurological deficits. Hippocampal apoptosis and cortical necrosis are histopathological correlates of neurofunctional sequelae in rodent models and are frequently observed in autopsy studies of patients who die of PM. In experimental PM, inhibition of matrix metalloproteinases (MMPs) and/or tumor necrosis factor (TNF)-converting enzyme (TACE) has been shown to reduce brain injury and the associated impairment of neurocognitive function. However, none of the compounds evaluated in these studies entered clinical development. Here, we evaluated two second-generation MMP and TACE inhibitors with higher selectivity and improved oral availability. Ro 32-3555 (Trocade, cipemastat) preferentially inhibits collagenases (MMP-1, -8, and -13) and gelatinase B (MMP-9), while Ro 32-7315 is an efficient inhibitor of TACE. PM was induced in infant rats by the intracisternal injection of live Streptococcus pneumoniae. Ro 32-3555 and Ro 32-7315 were injected intraperitoneally, starting at 3 h postinfection. Antibiotic (ceftriaxone) therapy was initiated at 18 h postinfection, and clinical parameters (weight, clinical score, mortality rate) were recorded. Myeloperoxidase activities, concentrations of cytokines and chemokines, concentrations of MMP-2 and MMP-9, and collagen concentrations were measured in the cerebrospinal fluid. Animals were sacrificed at 42 h postinfection, and their brains were assessed by histomorphometry for hippocampal apoptosis and cortical necrosis. Both compounds, while exhibiting disparate MMP and TACE inhibitory profiles, decreased hippocampal apoptosis and cortical injury. Ro 32-3555 reduced mortality rates and cerebrospinal fluid TNF, interleukin-1β (IL-1β) and collagen levels, while Ro 32-7315 reduced weight loss and cerebrospinal fluid TNF and IL-6 levels.

Fulminant bacterial meningitis

BACKGROUND

Fulminant bacterial meningitis is a rare host reaction to infection characterized by sudden onset, rapid deterioration, abrupt cerebral edema and refractory intracranial hypertension associated with an extremely high mortality rate.

METHODS

A search of all relevant medical literature since 1900 was conducted to clarify the nature of this entity and its medical management.

RESULTS

Fulminant meningitis occurs in a small percentage of all cases of bacterial meningitis, at all ages and with all infecting organisms. The mortality rate exceeds 50%. Descriptions of fulminant bacterial meningitis are found in medical literature from the preantibiotic era. Its incidence and clinical character have not changed since the introduction of antibiotics and advanced intensive care medicine. The explosive cerebral edema cannot be predicted, and the underlying molecular pathophysiology remains poorly understood. Vigorous neuroresuscitation and the use of adjunctive techniques to control the cerebral edema have not been shown to modify the extreme intracranial hypertension and risk of herniation.

CONCLUSION

Fulminant bacterial meningitis is an example of an aberrant host response to infection that challenges available medical intervention.

Metronidazole and hydroxymetronidazole central nervous system distribution: 1. microdialysis assessment of brain extracellular fluid concentrations in patients with acute brain injury

The distribution of metronidazole in the central nervous system has only been described based on cerebrospinal fluid data. However, extracellular fluid (ECF) concentrations may better predict its antimicrobial effect and/or side effects. We sought to explore by microdialysis brain ECF metronidazole distribution in patients with acute brain injury. Four brain-injured patients monitored by cerebral microdialysis received 500 mg of metronidazole over 0.5 h every 8 h. Brain dialysates and blood samples were collected at steady state over 8 h. Probe recoveries were evaluated by in vivo retrodialysis in each patient for metronidazole. Metronidazole and OH-metronidazole were assayed by high-pressure liquid chromatography, and a noncompartmental pharmacokinetic analysis was performed. Probe recovery was equal to 78.8% ± 1.3% for metronidazole in patients. Unbound brain metronidazole concentration-time curves were delayed compared to unbound plasma concentration-time curves but with a mean metronidazole unbound brain/plasma AUC0-τ ratio equal to 102% ± 19% (ranging from 87 to 124%). The unbound plasma concentration-time profiles for OH-metronidazole were flat, with mean average steady-state concentrations equal to 4.0 ± 0.7 μg ml(-1). This microdialysis study describes the steady-state brain distribution of metronidazole in patients and confirms its extensive distribution.

Bacterial meningitis: new therapeutic approaches

Bacterial meningitis remains a disease with high mortality and long-term morbidity. Outcome critically depends on the rapid initiation of effective antibiotic therapy. Since a further increase of the incidence of pathogens resistant to antibacterials can be expected both in community-acquired and nosocomial bacterial meningitis, the choice of an optimum initial empirical antibiotic regimen will gain significance. In this context, the use of antibiotics which are bactericidal but do not lyse bacteria, may emerge as a therapeutic option. Conversely, the role of corticosteroids, which decrease the entry of hydrophilic antibacterials into the cerebrospinal fluid, as adjunctive therapy will probably decline as a consequence of the increasing antibiotic resistance of bacteria causing meningitis. Consequent vaccination of all children at present is the most efficient manner to reduce disease burden.

Contribution of different pneumococcal virulence factors to experimental meningitis in mice

Background

Pneumococcal meningitis (PM) is a life-threatening disease with a high case-fatality rate and elevated risk for serious neurological sequelae. In this study, we investigated the contribution of three major virulence factors of Streptococcus pneumoniae, the capsule, pneumococcal surface protein A (PspA) and C (PspC), to the pathogenesis of experimental PM.

Methods

Mice were challenged by the intracranial route with the serotype 4 TIGR4 strain (wt) and three isogenic mutants devoid of PspA, PspC, and the capsule. Survival, bacterial counts, and brain histology were carried out. To study the interaction between S. pneumoniae mutants and microglia, phagocytosis and survival experiments were performed using the BV2 mouse microglial cell line.

Results

Virulence of the PspC mutant was comparable to that of TIGR4. In contrast, survival of animals challenged with the PspA mutant was significantly increased compared with the wt, and the mutant was also impaired at replicating in the brain and blood of infected mice. Brain histology indicated that all strains, except for the unencapsulated mutant, caused PM. Analysis of inflammation and damage in the brain of mice infected with TIGR4 or its unencapsulated mutant demonstrated that the rough strain was unable to induce inflammation and neuronal injury, even at high challenge doses. Results with BV2 cells showed no differences in phagocytic uptake between wt and mutants. In survival assays, however, the PspA mutant showed significantly reduced survival in microglia compared with the wt.

Conclusions

PspA contributed to PM pathogenesis possibly by interacting with microglia at early infection stages, while PspC had limited importance in the disease. The rough mutant did not cause brain inflammation, neuronal damage or mouse death, strengthening the key role of the capsule in PM.

Role of the cathelicidin-related antimicrobial peptide in inflammation and mortality in a mouse model of bacterial meningitis

Antimicrobial peptides (AP) are important components of the innate immune system, yet little is known about their expression and function in the brain. Our previous work revealed upregulated gene expression of cathelicidin-related AP (CRAMP) following bacterial meningitis in primary rat glial cells as well as bactericidal activity against frequent meningitis-causing bacteria. However, the effect of cathelicidin expression on the progression of inflammation and mortality in bacterial meningitis remains unknown. Therefore, we used CRAMP-deficient mice to investigate the effect of CRAMP on bacterial growth, inflammatory responses and mortality in meningitis. Meningitis was induced by intracerebral injection of type 3 Streptococcus pneumoniae. The degree of inflammation was analyzed in various brain regions by means of immunohistochemistry and real-time RT-PCR. CRAMP deficiency led to a higher mortality rate that was associated with increased bacterial titers in the cerebellum, blood and spleen as well as decreased meningeal neutrophil infiltration. CRAMP-deficient mice displayed a higher degree of glial cell activation that was accompanied by a more pronounced proinflammatory response. Taken together, this work provides insight into the important role of CRAMP as part of the innate immune defense against pathogens in bacterial CNS infections.

Cytokines and chemokines at the crossroads of neuroinflammation, neurodegeneration, and neuropathic pain

Cytokines and chemokines are proteins that coordinate the immune response throughout the body. The dysregulation of cytokines and chemokines is a central feature in the development of neuroinflammation, neurodegeneration, and demyelination both in the central and peripheral nervous systems and in conditions of neuropathic pain. Pathological states within the nervous system can lead to activation of microglia. The latter may mediate neuronal and glial cell injury and death through production of proinflammatory factors such as cytokines and chemokines. These then help to mobilize the adaptive immune response. Although inflammation may induce beneficial effects such as pathogen clearance and phagocytosis of apoptotic cells, uncontrolled inflammation can result in detrimental outcomes via the production of neurotoxic factors that exacerbate neurodegenerative pathology. In states of prolonged inflammation, continual activation and recruitment of effector cells can establish a feedback loop that perpetuates inflammation and ultimately results in neuronal injury. A critical balance between repair and proinflammatory factors determines the outcome of a neurodegenerative process. This review will focus on how cytokines and chemokines affect neuroinflammation and disease pathogenesis in bacterial meningitis and brain abscesses, Lyme neuroborreliosis, human immunodeficiency virus encephalitis, and neuropathic pain.

The Expression of Interleukin-1b and miRNA-146a in the Cerebral Cortex of Acute Escherichia Coli Meningitis Immature Rat Model

The main limitation to advances in treatment of bacterial meningitis and its complications is the incomplete knowledge of the pathogenesis and pathophysiology of this disease. The aim of this research is to detect the expression of interleukin (IL)-1β as pro-inflammatory cytokine and miRNA (miR)-146a as post transcriptional inflammation associated microRNA (miRNA) in the cerebral cortex of acute Escherichia coli (E. coli) meningitis immature rat model. Immature rats in the post natal day 11 (PN11) were used to construct a model of acute E. coli meningitis and served as controls. The expression of IL-1β and miR-146a were detected in the cerebral cortex by reverse transcription polymerase chain reaction (RT-PCR) and real-time quantitative PCR (qPCR) analysis respectively, 24 hours after bacterial inoculation. In the cerebral cortical tissue of acute E. coli meningitis immature rat model the IL-1β expression was significantly upregulated while the miR-146a expression was significantly downregulated. This study tried to add a new insight on the molecular basis of the E. coli meningitis pathogenesis at its very early stage through detecting the expression of IL-1β and miR-146a in the cerebral cortex of the infected immature rats. Consequently, modulation of the IL-1β- miR-146a axis may be a new target for treatment of acute E. coli meningitis.

Interactions between blood-borne Streptococcus pneumoniae and the blood-brain barrier preceding meningitis

Streptococcus pneumoniae (the pneumococcus) is a Gram-positive bacterium and the predominant cause of bacterial meningitis. Meningitis is thought to occur as the result of pneumococci crossing the blood-brain barrier to invade the Central Nervous System (CNS); yet little is known about the steps preceding immediate disease development. To study the interactions between pneumococci and the vascular endothelium of the blood-brain barrier prior to meningitis we used an established bacteremia-derived meningitis model in combination with immunofluorescent imaging. Brain tissue of mice infected with S. pneumoniae strain TIGR4, a clinical meningitis isolate, was investigated for the location of the bacteria in relation to the brain vasculature in various compartments. We observed that S. pneumoniae adhered preferentially to the subarachnoid vessels, and subsequently, over time, reached the more internal cerebral areas including the cerebral cortex, septum, and choroid plexus. Interestingly, pneumococci were not detected in the choroid plexus till 8 hours-post infection. In contrast to the lungs, little to no leukocyte recruitment to the brain was observed over time, though Iba-1 and GFAP staining showed that microglia and astrocytes were activated as soon as 1 hour post-infection. Our results imply that i) the local immune system of the brain is activated immediately upon entry of bacteria into the bloodstream and that ii) adhesion to the blood brain barrier is spatiotemporally controlled at different sites throughout the brain. These results provide new information on these two important steps towards the development of pneumococcal meningitis.

Acute bacterial meningitis: current review and treatment update

Bacterial meningitis is an infection of the meninges that can be infected by bacteria, virus, or fungus. The classic triad of bacterial meningitis consists of fever, neck stiffness, and altered mental status; headache is also another common symptom. Interventions for bacterial meningitis include prompt diagnosis, and initiation of antimicrobial therapy to optimize bacterial kill and decrease inflammatory response in the subarachnoid space. Nursing management consists of effective delivery of antibiotic therapy, fluid management, and supportive care.

How does the brain limit the severity of inflammation and tissue injury during bacterial meningitis?

The most devastating CNS bacterial infection, bacterial meningitis, has both acute and long-term neurologic consequences. The CNS defends itself against bacterial invasion through a combination of physical barriers (i.e. blood-brain barrier, meninges, and ependyma), which contain macrophages that express a range of pattern-recognition receptors that detect pathogens before they gain access to the CNS and cerebrospinal fluid. This activates an antipathogen response consisting of inflammatory cytokines, complement, and chemoattractants. Regulation of the antipathogen inflammatory response is essential for preventing irreversible brain injury and protecting stem cell populations in the ventricle wall. The severity of brain inflammation is regulated by the clearance of apoptotic inflammatory cells and neurons. Death signaling pathways are expressed by glia to stimulate apoptosis of neutrophils, lymphocytes, and damaged neurons and to regulate in flammation and remove necrotic cells. The emerging group of neuroimmunoregulatory molecules adjusts the balance of the anti-inflammatory and proinflammatory response to provide optimal conditions for effective clearance of pathogens and apoptotic cells but reduce the severity of the inflammatory response to prevent injury to brain cells, including stem cell populations. The neuroimmunoregulatory molecules and other CNS anti-inflammatory pathways represent potential therapeutic targets capable of reducing brain injury caused by bacterial infection.

Single nucleotide polymorphisms in pathogen recognition receptor genes are associated with susceptibility to meningococcal meningitis in a pediatric cohort

Bacterial meningitis (BM) is a serious infection of the central nervous system, frequently occurring in childhood and often resulting in hearing loss, learning disabilities, and encephalopathy. Previous studies showed that genetic variation in innate immune response genes affects susceptibility, severity, and outcome of BM. The aim of this study is to describe whether single nucleotide polymorphisms (SNPs) in pathogen recognition gene products are associated with susceptibility to develop BM in single genes analysis as well as SNP combinations. Genotype frequencies of seven SNPs, in five immune response genes encoding for Toll-like receptors (TLRs), nucleotide oligomerization domain (NOD) proteins and caspase-1 (CASP1), in 391 children with meningococcal meningitis (MM) and 82 children with pneumococcal meningitis were compared with a large cohort of 1141 ethnically matched healthy controls. Carriage of TLR4 +896 GG mutant predisposed to susceptibility to develop MM (p = 1.2*10⁻⁵, OR  = 9.4, 95% CI  = 3.0–29.2). The NOD2 SNP8 mutant was significantly more frequent in MM patients compared to controls (p = 0.0004, OR  = 12.2, 95% CI  = 2.6–57.8). Combined carriage of TLR2 +2477 and TLR4 +896 mutants was strongly associated with MM (p = 4.2*10⁻⁵, OR  = 8.6, 95% CI  = 2.7–27.3). A carrier trait of TLR4 +896 and NOD2 SNP8 mutants was also strongly associated with susceptibility to develop MM (p = 4.2*10⁻⁵, OR  = 10.6, 95% CI  = 2.9–38.6). This study associates SNPs in TLR4 and NOD2 with susceptibility to develop MM.

Streptococcus pneumoniae ClpP protease induces apoptosis via caspase-independent pathway in human neuroblastoma cells: cytoplasmic relocalization of p53

Streptococcus pneumoniae causes the most severe form of the bacterial meningitis which is the major cause of bacterial meningitis. Virulence factors produced by S. pneumoniae have been known to contribute significantly to the disease process. ClpP protease (ClpP) which is essential for virulence and survival under stress conditions in S. pneumoniae was examined for the ability to induce apoptosis and the mechanism of the induction of apoptosis in human neuron-like cells, SK-N-SH neuroblastoma cells. ClpP inhibited cell growth and induced apoptosis in SK-N-SH cells. Treatment with ClpP resulted in hypodiploid DNA contents, increased Bax/Bcl-2 ratio and induction of reactive oxygen species (ROS) production. The release of cytochrome c from mitochondria into the cytosol, which is an initiator of the activation of caspase cascades, was not observed in ClpP-treated cells. In addition, pretreatment with Z-Val-Ala-Asp-fluoromethylketone (Z-VAD-fmk), a broad spectrum caspase inhibitor, could not rescue apoptotic cells from ClpP toxicity. Coincidently, caspase-3 and -8 activation and cleavage of PARP were not detected. Moreover, caspase independent apoptosis-inducing factor (AIF) was released from mitochondria and translocated to the nucleus in response to ClpP. We also found that ClpP treatment resulted in the increase of p53 activity and cytoplasmic p53 levels were increased by ClpP, suggesting that functional activation of p53 is intact despite increased cytoplasmic accumulation. Taken together, these data suggest that ClpP contributes to neuronal damage in meningitis and provide further insight into the mechanisms underlying action of pneumococcal virulence factors during bacterial pathogenesis.

Microdialysis study of cefotaxime cerebral distribution in patients with acute brain injury

Central nervous system (CNS) antibiotic distribution was described mainly from cerebrospinal fluid data, and only few data exist on brain extracellular fluid concentrations. The aim of this study was to describe brain distribution of cefotaxime (2 g/8 h) by microdialysis in patients with acute brain injury who were treated for a lung infection. Microdialysis probes were inserted into healthy brain tissue of five critical care patients. Plasma and unbound brain concentrations were determined at steady state by high-performance liquid chromatography. In vivo recoveries were determined individually using retrodialysis by drug. Noncompartmental and compartmental pharmacokinetic analyses were performed. Unbound cefotaxime brain concentrations were much lower than corresponding plasma concentrations, with a mean cefotaxime unbound brain-to-plasma area under the curve ratio equal to 26.1 ± 12.1%. This result was in accordance with the brain input-to-brain output clearances ratio (CL(in,brain)/CL(out,brain)). Unbound brain concentrations were then simulated at two dosing regimens (4 g every 6 h or 8 h), and the time over the MICs (T>MIC) was estimated for breakpoints of susceptible and resistant Streptococcus pneumoniae strains. T>MIC was higher than 90% of the dosing interval for both dosing regimens for susceptible strains and only for 4 g every 6 h for resistant ones. In conclusion, brain distribution of cefotaxime was well described by microdialysis in patients and was limited.

Microglial activation and expression of immune-related genes in a rat ex vivo nervous system model after infection with Listeria monocytogenes

A wide variety of microorganisms has previously been identified as causes of brain infection. Among them, Listeria monocytogenes has a particular tropism for the central nervous system. To gain knowledge about the immune response elicited by L. monocytogenes in the brain, we used a rat ex vivo organotypic nervous system culture as a model for Listeria infection. Scanning electron microscopy (SEM) revealed that activated microglial cells showing a typical amoeboid morphology are quickly recruited to the surface of the explants after the infection. After bacterial engulfment, these cells appear to act as Trojan horses, releasing the engulfed bacteria inside the brain tissue. We describe cycles of microglial phagocytosis, necrotic cell death and the subsequent removal of cell debris for the first time. Furthermore, we used this ex vivo model to assess the expression profiles of immune relevant genes up to 24 h postinfection by means of q-PCR-arrays, finding that a number of inflammation-promoting genes are upregulated. Shortly after infection by L. monocytogenes, upregulated genes were those that encoded molecules involved in Th1 responses, being the Ccl2 chemokine and members of the interleukin1-β family the most abundant immunomodulatory signals expressed. After 5 h of infection, L. monocytogenes caused a substantial increase in the expression of TLR1 and TLR2 genes, as well as in several downstream genes of the TLR signaling pathways.

Should corticosteroids be used in bacterial meningitis in children?

Bacterial meningitis is one of the most serious infections in infants and children, with considerable morbidity and mortality. Despite the spreading of conjugated vaccines against Haemophilus influenzae type b (Hib), the most important pneumococcal serotypes and serogroup C meningococcus has reduced the incidence of this infection in developed countries, it still remains a global public health problem and an important cause of mortality and disability. Whether corticosteroids should be used as a complementary therapy to antibacterials is still not clear because of the disparate findings from clinical trials and clinical evidence. The aim of this review is to analyze the available evidence on the impact of corticosteroid therapy in infants and children with bacterial meningitis in developed countries in order to define whether they should be added routinely in the empiric therapy of such disease. Our analysis concluded that in high-income countries dexamethasone has shown good results to prevent hearing loss in Hib meningitis if administered before or at the same time as the first dose of antibiotics. Dexamethasone should be evaluated in pneumococcal meningitis: it may be less beneficial in children with delayed presentation to medical attention and may be unfavourable in case of cephalosporin-resistant pneumococci. On the contrary, there is no evidence to recommend the use of corticosteroids in meningococcal meningitis. Further studies that take into account the epidemiologic changes of recent years, consider enrolment based on the onset of symptoms and evaluate outcomes such as hearing loss and neurologic sequelae with advanced techniques are urgently needed.

Factors influencing neurological outcome of children with bacterial meningitis at the emergency department

We performed a cohort study of children who survived bacterial meningitis after the neonatal period at a single pediatric center in France over a 10-year period (1995-2004) to identify predictors of death and long-term neurological deficits in children with bacterial meningitis. We performed multivariate regression to determine independent predictors of death and neurologic deficits. We identified 101 children with bacterial meningitis of which 19 died during initial hospitalization. Need for mechanical ventilation [hazard ratio (HR) 11.5, 95 % confidence interval (CI) 2.4-55.5)] and thrombocytopenia defined as a platelet count <150 × 10(9) per liter (HR 0.6, 95 % CI 0.4-0.9) at presentation were associated with death during initial hospitalization. At final assessment, 42 of the 70 survivors had no neurologic deficits identified; 20 had a single deficit, and eight had multiple deficits. A delay in initiation of antibiotics (HR 1.3, 95 % CI 1.1-1.7) and hydrocephalus on computed tomographic scan (HR 2.6, 95 % CI 1.1-6.0) were associated with having one or more long-term neurologic deficits. Identification of children at risk of death or long-term neurologic sequelae may allow therapeutic interventions to be directed to children at the highest risk.

The diagnostic value of cytokine and nitric oxide concentrations in cerebrospinal fluid for the differential diagnosis of meningitis

PURPOSE

In several cases of meningitis routinely used diagnostic procedures are unable to identify the cause of this disease. The objective of the present study was to determine whether proinflammatory cytokine (tumour necrosis factor (TNF-α), interleukin-1β (IL-1β), interleukin-8 (IL-8)) and nitric oxide (NO) concentrations in the CSF are useful markers for the differential diagnosis of meningitis.

MATERIAL AND METHODS

Sixty-seven patients (42 patients with bacterial meningitis and 25 patients with viral meningitis) were included in the present study. In the investigated group, the TNF-α, IL-1β and IL-8 concentrations in the CSF samples collected on the day of admission were assessed. Furthermore, the NO concentrations were assessed in 23 patients.

RESULTS

The results revealed that the measurement of proinflammatory cytokines in CSF can aid in a differential diagnosis. In particular, a high concentration of TNF-α may be a sensitive and specific marker of a bacterial aetiology of the neuroinfection. In the present study, TNF-α concentrations greater than 75.8 pg/ml differentiated between bacterial and viral meningitis with 100% sensitivity and specificity. The NO concentration in the CSF was also significantly greater in patients with bacterial meningitis than in those with viral meningitis.

CONCLUSIONS

The assessment of TNF-α, IL-1β and IL-8 concentrations in the CSF is useful in the differential diagnosis of neuroinfection. Because many factors may influence NO production in the central nervous system (CNS), it is not clear whether NO values can be used for the differential diagnosis of meningitis, and further studies are required.

Toll-like receptor 2 ligand pretreatment attenuates retinal microglial inflammatory response but enhances phagocytic activity toward Staphylococcus aureus

Staphylococcus aureus is a leading cause of severe endophthalmitis, which often results in vision loss in some patients. Previously, we showed that Toll-like receptor 2 (TLR2) ligand pretreatment prevented the development of staphylococcal endophthalmitis in mice and suggested that microglia might be involved in this protective effect (Kumar A, Singh CN, Glybina IV, Mahmoud TH, Yu FS. J. Infect. Dis. 201:255-263, 2010). The aim of the present study was to understand how microglial innate response is modulated by TLR2 ligand pretreatment. Here, we demonstrate that S. aureus infection increased the CD11b(+) CD45(+) microglial/macrophage population in the C57BL/6 mouse retina. Using cultured primary retinal microglia and a murine microglial cell line (BV-2), we found that these cells express TLR2 and that its expression is increased upon stimulation with bacteria or an exclusive TLR2 ligand, Pam3Cys. Furthermore, challenge of primary retinal microglia with S. aureus and its cell wall components peptidoglycan (PGN) and lipoteichoic acid (LTA) induced the secretion of proinflammatory mediators (tumor necrosis factor alpha [TNF-α] and MIP-2). This innate response was attenuated by a function-blocking anti-TLR2 antibody or by small interfering RNA (siRNA) knockdown of TLR2. In order to assess the modulation of the innate response, microglia were pretreated with a low dose (0.1 or 1 μg/ml) of Pam3Cys and then challenged with live S. aureus. Our data showed that S. aureus-induced production of proinflammatory mediators is dramatically reduced in pretreated microglia. Importantly, microglia pretreated with the TLR2 agonist phagocytosed significantly more bacteria than unstimulated cells. Together, our data suggest that TLR2 plays an important role in retinal microglial innate response to S. aureus, and its sensitization inhibits inflammatory response while enhancing phagocytic activity.

Bacterial meningitis: current therapy and possible future treatment options

Despite targeted therapy, case-fatality rates and neurologic sequelae of bacterial meningitis remain unacceptably high. The poor outcome is mainly due to secondary systemic and intracranial complications. These complications seem to be both a consequence of the inflammatory response to the invading pathogen and release of bacterial components by the pathogen itself. Therefore, within the last decades, research has focused on the mechanism underlying immune regulation and the inhibition of bacterial lysis in order to identify new targets for adjuvant therapy. The scope of this article is to give an overview on current treatment strategies of bacterial meningitis, to summarize new insights on the pathophysiology of bacterial meningitis, and to give an outlook on new treatment strategies derived from experimental models.

Role of endogenous biological response modifiers in pathogenesis of infectious diseases

Biologic response modifiers (BRMs) interact with the host immune system and modify the immune response. BRMs can be therapeutically used to restore, augment, or dampen the host immune response. Although they have been used for decades, their clinical applications have been expanded in the past decade for diagnosis and treatment of many diseases including cancers, immunologic disorders, and infections. This article discusses endogenous biological response modifiers (ie, naturally occurring immunomodulators as a part of the host immune system), which play vital roles as regulators of both innate and adaptive immune responses.

Pathogenesis and pathophysiology of pneumococcal meningitis

Pneumococcal meningitis continues to be associated with high rates of mortality and long-term neurological sequelae. The most common route of infection starts by nasopharyngeal colonization by Streptococcus pneumoniae, which must avoid mucosal entrapment and evade the host immune system after local activation. During invasive disease, pneumococcal epithelial adhesion is followed by bloodstream invasion and activation of the complement and coagulation systems. The release of inflammatory mediators facilitates pneumococcal crossing of the blood-brain barrier into the brain, where the bacteria multiply freely and trigger activation of circulating antigen-presenting cells and resident microglial cells. The resulting massive inflammation leads to further neutrophil recruitment and inflammation, resulting in the well-known features of bacterial meningitis, including cerebrospinal fluid pleocytosis, cochlear damage, cerebral edema, hydrocephalus, and cerebrovascular complications. Experimental animal models continue to further our understanding of the pathophysiology of pneumococcal meningitis and provide the platform for the development of new adjuvant treatments and antimicrobial therapy. This review discusses the most recent views on the pathophysiology of pneumococcal meningitis, as well as potential targets for (adjunctive) therapy.

Long-term intrathecal infusion of outer surface protein C from Borrelia burgdorferi causes axonal damage

Lyme neuroborreliosis (LNB) is the most frequent tick-borne infectious disease of the central nervous system. In acute LNB and the rare chronic state of infection, patients can experience cognitive deficits such as attention and memory disturbances. During LNB, single compounds of Borrelia burgdorferi sensu lato are released into the subarachnoid space.To investigate the pathogenesis of neurologic dysfunction in LNB, we determined that the outer surface protein C (OspC), a major virulence factor of B. burgdorferi, stimulated mouse microglial cells in a dose-dependent manner to release nitric oxide (EC50 = 0.24 mg/L) in vitro. To mimic pathophysiologic conditions of long-term release of this bacterial component in vivo, we treated C57BL/6 mice with recombinant OspC from Borrelia garinii or buffer by intraventricular infusion and tested them for behavioral deficits. After 4weeks, brains were examined by routine histology and immunohistochemistry. Assessment of spatial learning and memory of treated mice during OspC exposure did not reveal significant differences from controls. Continuous exposure to intrathecal B. burgdorferi OspC led to activation of microglia and axonal damage without demonstrable cognitive impairment in experimental mice. These results suggest that long-term intrathecal exposure to OspC resulted in axonal damage that may underlie the neurologic manifestations in chronic LNB.

No increase in headache after previous intracranial infections: a historical cohort study (HUNT)

BACKGROUND AND PURPOSE

Despite the absence of robust scientific evidence, it is today generally accepted that the acute headache typical for intracranial infections can develop into permanent headache complaints. This widespread concept was explored in the first, large, longitudinal, population-based study.

METHODS

Data on confirmed exposure to intracranial infections amongst all adult inhabitants in a geographical area during a 20-year period were assembled from hospital records. Surviving individuals were later invited to the third Nord-Trøndelag Health Survey (HUNT 3), where 39,690 (42%) of 94,194 invited inhabitants aged ≥20 years responded to a validated headache questionnaire. Using logistic regression, the 1-year prevalence of headache and its subtypes according to the diagnostic criteria of the International Headache Society was assessed and compared between those with and without previous confirmed intracranial infection. Age and sex were used as covariates.

RESULTS

Overall, 43 participants were identified with earlier intracranial infection, whereof three had more than one infection: bacterial meningitis (n=19), lymphocytic meningitis (n=18), encephalitis (n=9), and brain abscess (n=1).The mean interval from infection to participation in HUNT 3 was 11.2 (range 1.5-19.7) years. There was no significant increase in the prevalence of headache (OR 1.10, 95% CI 0.58-2.07), its subtypes (migraine, or tension-type headache), or chronic daily headache (OR 1.85, 95% CI 0.45-7.68) amongst participants with previous intracranial infection compared with the surrounding population.

CONCLUSIONS

This study challenges the existence of chronic post-bacterial meningitis headache and does not indicate the presence of other long-term headaches induced by intracranial infection.

Aquaporins AQP1 and AQP4 in the cerebrospinal fluid of bacterial meningitis patients

Aquaporins facilitate water transport through cell membranes. Due to the localization of AQP1 and AQP4 in the brain, they might contribute to cerebral edema. Our study aimed to determine whether AQP1 and AQP4 can be measured in cerebrospinal fluid (CSF), and whether there is a difference in AQP1 and AQP4 concentration between patients with bacterial meningitis (BM) and healthy controls. AQP1 and AQP4 concentrations in CSF from 35 patients with BM and 27 controls were analyzed using a commercial ELISA. The mean concentration of AQP1 in CSF was significantly elevated in patients with BM (BM: 3.8±3.4ng/ml, controls: 0.8±0.5ng/ml; p<0.001). AQP4 had a tendency to be increased, however the difference was not significant (BM: 1.8±3.1ng/ml, controls: 0.1±0.2ng/ml; p=0.092). AQP1 and AQP4 in CSF of BM patients were inversely correlated (r=-0.47, p=0.004). We could not find any other correlation between concentration of AQP1 or AQP4 in CSF and CSF leukocytes, lactate, protein, albumin CSF/serum ratio, age, a prediction score, an outcome score or the Glasgow Coma Scale at admission in patients with BM. Control patients displayed a correlation between AQP1 and the albumin CSF/serum ratio (r=0.390, p=0.040). This is the first study that detected AQP1 and AQP4 in CSF. Whether the significant elevation of AQP1 is due to a higher expression and subsequent shedding into CSF or a BM-induced cell damage needs to be determined.

Dynamic changes of TrkB gene expression in Streptococcus pneumoniae meningitis after treatment with antibiotics and dexamethasone

BACKGROUND

Although more and more new potent antibiotics have been used, the incidence of neurological sequelae of Streptococcus pneumoniae meningitis has not improved in children over the last decade. The expression of TrkB mRNA, a receptor of brain-derived neurotrophic factor, is associated with the incidence of neurological sequelae of Streptococcus pneumoniae meningitis.

METHODS

Rats of 3 weeks old were used to construct a model of Streptococcus pneumoniae meningitis and served as normal controls. They were administered with antibiotics or antibiotics plus dexamethasone, respectively. The expression of the TrkB gene was detected in the brain by in situ hybridization.

RESULTS

In the brains of Streptococcus pneumoniae inoculated rats, TrkB mRNA was significantly up-regulated after inoculation for 24 hours, and then down-regulated in a dose-dependent manner after treatment with antibiotics. This up-regulation was seen after treatment with antibiotics plus dexamethasone. TrkB mRNA expression was also observed in some infiltrating inflammatory cells.

CONCLUSIONS

The results of the study support the hypothesis that TrkB signal transduction pathways might play an important role in Streptococcus pneumoniae meningitis, probably by protecting the brain from damage. The role of TrkB might be weakened after the treatment with antibiotics. Our findings suggest that targeting TrkB receptors might be a rational strategy for prevention of neurological sequelae caused by Streptococcus pneumoniae meningitis.