The formyl peptide receptor like-1 and scavenger receptor MARCO are involved in glial cell activation in bacterial meningitis

Recent studies have suggested that the scavenger receptor MARCO (macrophage receptor with collagenous structure) mediates activation of the immune response in bacterial infection of the central nervous system (CNS). The chemotactic G-protein-coupled receptor (GPCR) formyl-peptide-receptor like-1 (FPRL1) plays an essential role in the inflammatory responses of host defence mechanisms and neurodegenerative disorders such as Alzheimer's disease (AD). Expression of the antimicrobial peptide cathelicidin CRAMP/LL-37 is up-regulated in bacterial meningitis, but the mechanisms underlying CRAMP expression are far from clear.

Meningitis caused by Mycoplasma mycoides subspecies capri in a goat

A 2-year-old, female goat from Connecticut was submitted for necropsy with a 5-day history of pyrexia and intermittent neurologic signs, including nystagmus, seizures, and circling. Postmortem examination revealed suppurative meningitis. Histologic examination of the brain revealed that the meninges were diffusely infiltrated by moderate numbers of lymphocytes, macrophages, and fibrin, with scattered foci of dense neutrophilic infiltrate. Culture of pus and brainstem yielded typical mycoplasma colonies. DNA sequencing of the 16S ribosomal RNA gene revealed 99% sequence homology with Mycoplasma mycoides subspecies capri and Mycoplasma mycoides subspecies mycoides Large Colony biotype, which are genetically indistinguishable and likely to be combined as a single subspecies labeled M. mycoides subsp. capri. The present case is unusual in that not only are mycoplasma an uncommon cause of meningitis in animals, but additionally, in that all other reported cases of mycoplasma meningitis in goats, systemic lesions were also present. In the present case, meningitis was the only lesion, thus illustrating the need to consider mycoplasma as a differential diagnosis for meningitis in goats.

Inflammasome-dependent IFN-γ drives pathogenesis in Streptococcus pneumoniae meningitis

The pathology associated with Streptococcus pneumoniae meningitis results largely from activation of immune-associated pathways. We systematically investigated the production of IFN subtypes, as well as their influence on pathology, in a mouse model of S. pneumoniae meningitis. Despite the occurrence of a mixed IFN type I/II gene signature, no evidence for production or involvement of type I IFNs in disease progression was found. In contrast, type II IFN (IFN-γ) was strongly induced, and IFN-γ(-/-) mice were significantly protected from severe disease. Using intracellular cytokine staining and targeted cell-depletion approaches, NK cells were found to be the dominant source of IFN-γ. Furthermore, production of IFN-γ was found to be dependent upon ASC and IL-18, indicating that an ASC-dependent inflammasome pathway was responsible for mediating IFN-γ induction. The influence of IFN-γ gene deletion on a range of processes known to be involved in bacterial meningitis pathogenesis was examined. Although neutrophil numbers in the brain were similar in infected wild-type and IFN-γ(-/-) mice, both monocyte recruitment and CCL2 production were less in infected IFN-γ(-/-) mice compared with infected wild-type controls. Additionally, gene expression of NO synthase was strongly diminished in infected IFN-γ(-/-) mice compared with infected controls. Finally, bacterial clearance was enhanced in IFN-γ(-/-) mice, although the underlying mechanism remains unclear. Together, these data suggest that inflammasome-dependent IFN-γ contributes via multiple pathways to pathology during S. pneumoniae meningitis.

Daptomycin is more efficacious than vancomycin against a methicillin-susceptible Staphylococcus aureus in experimental meningitis

OBJECTIVES: To test the efficacy of daptomycin, a cyclic lipopeptide antibiotic, against a methicillin-susceptible Staphylococcus aureus strain in experimental rabbit meningitis and to determine its penetration into non-inflamed and inflamed meninges RESULTS: Over a treatment period of 8 h, daptomycin (15 mg/kg) was significantly superior to the comparator regimen vancomycin (-4.54 +/- 1.12 log(10)/mL for daptomycin versus -3.43 +/- 1.17 log(10)/mL for vancomycin). Daptomycin managed to sterilize 6 out of 10 CSFs compared with 4 out of 10 for vancomycin. The penetration of daptomycin into inflamed meninges was approximately 5% and approximately 2% into non-inflamed meninges. CONCLUSIONS: The superior bactericidal activity of daptomycin was confirmed in vivo and in time-killing assays in vitro.

Gelatinase B [matrix metalloproteinase (MMP)-9] and collagenases (MMP-8/-13) are upregulated in cerebrospinal fluid during aseptic and bacterial meningitis in children

We investigated the protein expression of gelatinases [matrix metalloproteinase (MMP)-2 and -9] and collagenases (MMP-8 and -13) in cerebrospinal fluid (CSF) from patients with bacterial (BM, n = 17) and aseptic (AM, n = 14) meningitis. In both, MMP-8 and -9 were increased in 100% of patients, whereas MMP-13 was detectable in 53% and 82% respectively. Three patients with clinical signs of meningitis, without CSF pleocytosis, scored positive for all three MMPs. MMP-8 appeared in two isoforms, granulocyte-type [polymorphonuclear cell (PMN)] and fibroblast/macrophage (F/M) MMP-8. Analysis of kinetic changes from serial lumbar punctures showed that these MMPs are independently regulated, and correlate only partly with CSF cytosis or levels of the endogenous inhibitor, tissue inhibitor of matrix metalloproteinase-1. In vitro, T cells, peripheral blood mononuclear cells (PBMCs) and granulocytes (PMN) release MMP-8 and -9, whereas MMP-13 could be found only in the former two cell types. Using models of exogenous (n-formyl-Met-Leu-Phe, T cell receptor cross-linking) and host-derived stimuli (interleukin-2), the kinetics and the release of the MMP-8, -9 and -13 showed strong variation between these immune cells and suggest release from preformed stocks. In addition, MMP-9 is also synthesized de novo in PBMCs and T cells. In conclusion, invading immune cells contribute only partially to MMPs in CSF during meningitis, and parenchymal cells are an equally relevant source. In this context, in patients with clinical signs of meningitis, but without CSF pleocytosis, MMPs seem to be a highly sensitive marker for intrathecal inflammation. The present data support the concept that broad-spectrum enzyme inhibition targeting gelatinases and collagenases is a potential strategy for adjunctive therapy in infectious meningitis.

Temporal expression of inflammatory mediators in brain basilar artery vasculitis and cerebrospinal fluid of rabbits with coccidioidal meningitis

Strokes due to transmural vasculitis associated with coccidioidal meningitis result in significant morbidity and mortality. The immunological and inflammatory processes responsible are poorly understood. To determine the inflammatory mediators, i.e. cytokines, chemokines, iNOS, matrix metalloproteinase-9 (MMP-9), that possibly contribute to vasculitis, temporal mRNA expression in brain basilar artery samples and MMP-9 protein in the CSF of male NZW rabbits infected intracisternally with 6.5 x 10(4) arthroconidia of Coccidioides immitis were assessed. Five infected and 3 sham-injected rabbits at each time point were euthanized 4, 9, 14 and 20 days post infection. All infected rabbits had neurological abnormalities and severe vasculitis in the basilar arteries on days 9-20. In basilar arteries of infected animals versus controls, mRNAs encoding for IL-6, iNOS, IFN-gamma, IL-2, MCP-1, IL-1beta, IL-10, TNF-alpha, CCR-1, MMP-9, TGF-beta, as well as MMP-9 protein in CSF, were found to be significantly up-regulated. Thus, this study identified inflammatory mediators associated with CNS vasculitis and meningitis due to C. immitis infection. Assessment of the individual contribution of each mediator to vasculitis may offer novel approaches to the treatment of coccidioidal CNS infection. This study also provides unique methodology for immunology studies in a rabbit model.

No temporal association between influenza outbreaks and invasive pneumococcal infections

OBJECTIVE: To assess whether the influenza peak in populations precedes the annual peak for invasive pneumococcal infections (IPI) in winter. DESIGN: Ecological study. Active surveillance data on influenza A and IPI in children up to 16 years of age collected from 1997 to 2003 were analysed. SETTING: Paediatric hospitals in Germany. Patients: Children under 16 years of age. RESULTS: In all years under study, the influenza A season did not appear to affect the IPI season (p = 0.49). Specifically, the influenza peak never preceded the IPI peak. CONCLUSION: On a population level there was no indication that the annual influenza epidemic triggered the winter increase in the IPI rate or the peak of the IPI distribution in children.

Cerebral vasculature is the major target of oxidative protein alterations in bacterial meningitis

We have previously shown that antioxidants such as a-phenyl-tert-butyl nitrone or N-acetylcysteine attenuate cortical neuronal injury in infant rats with bacterial meningitis, suggesting that oxidative alterations play an important role in this disease. However, the precise mechanism(s) by which antioxidants inhibit this injury remain(s) unclear. We therefore studied the extent and location of protein oxidation in the brain using various biochemical and immunochemical methods. In cortical parenchyma, a trend for increased protein carbonyls was not evident until 21 hours after infection and the activity of glutamine synthetase (another index of protein oxidation) remained unchanged. Consistent with these results, there was no evidence for oxidative alterations in the cortex by various immunohistochemical methods even in cortical lesions. In contrast, there was a marked increase in carbonyls, 4-hydroxynonenal protein adducts and manganese superoxide dismutase in the cerebral vasculature. Elevated lipid peroxidation was also observed in cerebrospinal fluid and occasionally in the hippocampus. All of these oxidative alterations were inhibited by treatment of infected animals with N-acetylcysteine or alpha-phenyl-tert-butyl nitrone. Because N-acetylcysteine does not readily cross the blood-brain barrier and has no effect on the loss of endogenous brain antioxidants, its neuroprotective effect is likely based on extraparenchymal action such as inhibition of vascular oxidative alterations.

Current concepts in the pathogenesis of meningitis caused by Streptococcus pneumoniae

In spite of improved antimicrobial therapy, bacterial meningitis still results in brain damage leading to significant long-term neurological sequelae in a substantial number of survivors, as confirmed by several recent studies. Meningitis caused by Streptococcus pneumoniae is associated with a particularly severe outcome. Experimental studies over the past few years have increased our understanding of the molecular mechanisms underlying the events that ultimately lead to brain damage during meningitis. Necrotic damage to the cerebral cortex is at least partly mediated by ischemia and oxygen radicals and therefore offers a promising target for adjunctive therapeutic intervention. Neuronal apoptosis in the hippocampus may represent the major pathological process responsible for cognitive impairment and learning disabilities in survivors. However, the mechanisms involved in causing this damage remain largely unknown. Anti-inflammatory treatment with corticosteroids aggravates hippocampal damage, thus underlining the potential shortcomings of current adjuvant strategies. In contrast, the combined inhibition of matrix metalloproteinase and tumour necrosis factor-alpha converting enzyme protected both the cortex and hippocampus in experimental meningitis, and may represent a promising new approach to adjunctive therapy. It is the hope that a more refined molecular understanding of the pathogenesis of brain damage during bacterial meningitis will lead to new adjunctive therapies.

Oxidative stress in brain during experimental bacterial meningitis: differential effects of alpha-phenyl-tert-butyl nitrone and N-acetylcysteine treatment

Antioxidant treatment has previously been shown to be neuroprotective in experimental bacterial meningitis. To obtain quantitative evidence for oxidative stress in this disease, we measured the major brain antioxidants ascorbate and reduced glutathione, and the lipid peroxidation endproduct malondialdehyde in the cortex of infant rats infected with Streptococcus pneumoniae. Cortical levels of the two antioxidants were markedly decreased 22 h after infection, when animals were severely ill. Total pyridine nucleotide levels in the cortex were unaltered, suggesting that the loss of the two antioxidants was not due to cell necrosis. Bacterial meningitis was accompanied by a moderate, significant increase in cortical malondialdehyde. While treatment with either of the antioxidants alpha-phenyl-tert-butyl nitrone or N-acetylcysteine significantly inhibited this increase, only the former attenuated the loss of endogenous antioxidants. Cerebrospinal fluid bacterial titer, nitrite and nitrate levels, and myeloperoxidase activity at 18 h after infection were unaffected by antioxidant treatment, suggesting that they acted by mechanisms other than modulation of inflammation. The results demonstrate that bacterial meningitis is accompanied by oxidative stress in the brain parenchyma. Furthermore, increased cortical lipid peroxidation does not appear to be the result of parenchymal oxidative stress, because it was prevented by NAC, which had no effect on the loss of brain antioxidants.

Marked elevation in cortical urate and xanthine oxidoreductase activity in experimental bacterial meningitis

Experimental bacterial meningitis due to Streptococcus pneumoniae in infant rats was associated with a time-dependent increase in CSF and cortical urate that was approximately 30-fold elevated at 22 h after infection compared to baseline. This increase was mirrored by a 20-fold rise in cortical xanthine oxidoreductase activity. The relative proportion of the oxidant-producing xanthine oxidase to total activity did not increase, however. Blood plasma levels of urate also increased during infection, but part of this was as a consequence of dehydration, as reflected by elevated ascorbate concentrations in the plasma. Administration of the radical scavenger alpha-phenyl-tert-butyl nitrone, previously shown to be neuroprotective in the present model, did not significantly affect either xanthine dehydrogenase or xanthine oxidase activity, and increased even further cortical accumulation of urate. Treatment with the xanthine oxidoreductase inhibitor allopurinol inhibited CSF urate levels earlier than those in blood plasma, supporting the notion that urate was produced within the brain. However, this treatment did not prevent the loss of ascorbate and reduced glutathione in the cortex and CSF. Together with data from the literature, the results strongly suggest that xanthine oxidase is not a major cause of oxidative stress in bacterial meningitis and that urate formation due to induction of xanthine oxidoreductase in the brain may in fact represent a protective response.

Rapid diagnosis of experimental meningitis by bacterial heat production in cerebrospinal fluid

BACKGROUND: Calorimetry is a nonspecific technique which allows direct measurement of heat generated by biological processes in the living cell. We evaluated the potential of calorimetry for rapid detection of bacterial growth in cerebrospinal fluid (CSF) in a rat model of bacterial meningitis. METHODS: Infant rats were infected on postnatal day 11 by direct intracisternal injection with either Streptococcus pneumoniae, Neisseria meningitidis or Listeria monocytogenes. Control animals were injected with sterile saline or heat-inactivated S. pneumoniae. CSF was obtained at 18 hours after infection for quantitative cultures and heat flow measurement. For calorimetry, 10 microl and 1 microl CSF were inoculated in calorimetry ampoules containing 3 ml trypticase soy broth (TSB). RESULTS: The mean bacterial titer (+/- SD) in CSF was 1.5 +/- 0.6 x 108 for S. pneumoniae, 1.3 +/- 0.3 x 106 for N. meningitidis and 3.5 +/- 2.2 x 104 for L. monocytogenes. Calorimetric detection time was defined as the time until heat flow signal exceeded 10 microW. Heat signal was detected in 10-microl CSF samples from all infected animals with a mean (+/- SD) detection time of 1.5 +/- 0.2 hours for S. pneumoniae, 3.9 +/- 0.7 hours for N. meningitidis and 9.1 +/- 0.5 hours for L. monocytogenes. CSF samples from non-infected animals generated no increasing heat flow (<10 microW). The total heat was the highest in S. pneumoniae ranging from 6.7 to 7.5 Joules, followed by L. monocytogenes (5.6 to 6.1 Joules) and N. meningitidis (3.5 to 4.4 Joules). The lowest detectable bacterial titer by calorimetry was 2 cfu for S. pneumoniae, 4 cfu for N. meningitidis and 7 cfu for L. monocytogenes. CONCLUSION: By means of calorimetry, detection times of <4 hours for S. pneumoniae and N. meningitidis and <10 hours for Listeria monocytogenes using as little as 10 microl CSF were achieved. Calorimetry is a new diagnostic method allowing rapid and accurate diagnosis of bacterial meningitis from a small volume of CSF.