Causative Agent Of Bacterial Meningitis Research Articles

The structural basis of transferrin sequestration by transferrin-binding protein B

Neisseria meningitidis, the causative agent of bacterial meningitis, acquires the essential element iron from the host glycoprotein transferrin (Tf) during infection via a surface Tf receptor system composed of proteins TbpA and TbpB. Here in we present the crystal structures of TbpB from N. meningitidis, in its apo form and in complex with human Tf (hTf). The structure reveals how TbpB sequesters hTf and initiates iron release from hTf.

Prophylactic and therapeutic targeting of the neurokinin-1 receptor limits neuroinflammation in a murine model of pneumococcal meningitis.

There is increasing evidence that the tachykinin substance P (SP) can augment inflammatory immune responses within the CNS. We have recently demonstrated that resident CNS cells express high-affinity receptors for this neuropeptide (neurokinin-1 receptors [NK-1R]), and we have shown that SP can significantly augment glial inflammatory responses to clinically relevant Gram-negative bacteria. Furthermore, we provided evidence that endogenous SP/NK-1R interactions are an essential component in the initiation and/or progression of CNS inflammation following in vivo exposure to these pathogens. In this study, we demonstrate that SP similarly enhances inflammatory glial responses to the major Gram-positive causative agent of bacterial meningitis, Streptococcus pneumoniae, and show that endogenous SP/NK-1R interactions play a critical role in the development of CNS inflammation in an in vivo model of pneumococcal meningitis. Importantly, we provide the first demonstration, to our knowledge, that pharmacological targeting of the NK-1R not only prevents the development of damaging inflammation when administered prophylactically, but can also limit or reverse neuroinflammation associated with an established streptococcal CNS infection when delivered therapeutically. We show that an NK-1R antagonist attenuates increases in CNS inflammatory cytokine levels and decreases in immunosuppressive cytokine production associated with an ongoing S. pneumoniae infection. Furthermore, we demonstrate that such a therapeutic intervention reverses infection-associated gliosis and demyelination in the absence of changes in CNS bacterial burden. Together, these results suggest that targeting SP/NK-1R interactions is a strategy worthy of further study for the treatment of microbially induced neuroinflammation.

The transposon-like Correia elements encode numerous strong promoters and provide a potential new mechanism for phase variation in the meningococcus.

Neisseria meningitidis is the primary causative agent of bacterial meningitis. The genome is rich in repetitive DNA and almost 2% is occupied by a diminutive transposon called the Correia element. Here we report a bioinformatic analysis defining eight subtypes of the element with four distinct types of ends. Transcriptional analysis, using PCR and a lacZ reporter system, revealed that two ends in particular encode strong promoters. The activity of the strongest promoter is dictated by a recurrent polymorphism (Y128) at the right end of the element. We highlight examples of elements that appear to drive transcription of adjacent genes and others that may express small non-coding RNAs. Pair-wise comparisons between three meningococcal genomes revealed that no more than two-thirds of Correia elements maintain their subtype at any particular locus. This is due to recombinational class switching between elements in a single strain. Upon switching subtype, a new allele is available to spread through the population by natural transformation. This process may represent a hitherto unrecognized mechanism for phase variation in the meningococcus. We conclude that the strain-to-strain variability of the Correia elements, and the large number of strong promoters encoded by them, allows for potentially widespread effects within the population as a whole. By defining the strength of the promoters encoded by the eight subtypes of Correia ends, we provide a resource that allows the transcriptional effects of a particular subtype at a given locus to be predicted.

Meningitis bacteriana por bacilos gramnegativos en adultos

Gram-negative bacilli are causative agents of bacterial meningitis in the neonatal period but rarely cause meningitis in adults without risk factors. To report on meningitis due to gram-negative bacilli (MGNB) in adults diagnosed in a hospital over a 25-year period. We reviewed the medical records of all patients with an age > or = 14 years who had been diagnosed with MGNB between 1982 and 2006. Fifteen cases of MGNB are included (10.5% of the cases of bacterial meningitis with an identified aetiology), with a mean age of 48 years (14-79). Twelve (80%) were post-operative: recent neurosurgery (9 cases, 75%) and having a neurosurgical device (8 cases, 67%) were risk factors. Three (20%) were spontaneous: two were of a urinary origin and one had an undetermined origin. The aetiology was: Pseudomonas aeruginosa (3 cases), Escherichia coli (3 cases), Enterobacter aerogenes (2 cases), Pseudomonas fluorescens (1 case), Klebsiella pneumoniae (1 case), Morganella morganii (1 case), Acinetobacter anitratus (1 case), Acinetobacter iwoffii (1 case) and Flavobacterium brevis (1 case); in one patient with Gram positive staining for gram-negative bacilli, the culture was negative, and three of them (20%) were mixed infections (Staphylococcus spp.). Three patients (20%) died. In adults, gram-negative bacilli rarely cause spontaneous meningitis, but are a common causation of post-neurosurgical meningitis and in those with neurosurgical devices. The mortality rate of MGNB is high.

Structural studies of Neisseria meningitidis outer membrane protein PorB and the mechanism of recognition by toll‐like receptor 2

Neisseria meningitis is one of the causative agents of bacterial meningitis, which is hallmarked by the inflammation of the lining that surrounds the brain and spinal cord. The N. meningitidis outer membrane protein (OMP) PorB has been identified as an attractive candidate for the development of a vaccine against meningitis. In vivo, PorB activates the toll‐like receptor (TLR) pathway to trigger the innate immune system. To provide a framework for the mechanism of PorB recognition by TLRs, each protein is being studied both in isolation and in complex. The x‐ray crystal structure of the N. meningitidis PorB was determined to 2.3 Åresolution. PorB forms a 16‐stranded β‐barrel surrounding a central pore. Solute transport through this pore may be aided by the presence of an internal plug formed exclusively from long, folded inter‐strand loops. Initial studies combining purified PorB and the ectodomain of TLR2 identifies the formation of a 420 kD complex, demonstrating that PorB directly interacts with the ectodomain of TLR2 in vitro. The molecular weight of this complex is consistent with a 6:2 PorB:TLR2 stoichiometric ratio and directly shows complex formation between a TLR and an OMP for the first time.

The Structure and Transcriptional Analysis of a Global Regulator from Neisseria meningitidis

Neisseria meningitidis, a causative agent of bacterial meningitis, has a relatively small repertoire of transcription factors, including NMB0573 (annotated AsnC), a member of the Lrp-AsnC family of regulators that are widely expressed in both Bacteria and Archaea. In the present study we show that NMB0573 binds to l-leucine and l-methionine and have solved the structure of the protein with and without bound amino acids. This has shown, for the first time that amino acid binding does not induce significant conformational changes in the structure of an AsnC/Lrp regulator although it does appear to stabilize the octameric assembly of the protein. Transcriptional profiling of wild-type and NMB0573 knock-out strains of N. meningitidis has shown that NMB0573 is associated with an adaptive response to nutrient poor conditions reflected in a reduction in major surface protein expression. On the basis of its structure and the transcriptional response, we propose that NMB0573 is a global regulator in Neisseria controlling responses to nutrient availability through indicators of general amino acid abundance: leucine and methionine.

The pathogen Neisseria meningitidis requires oxygen, but supplements growth by denitrification. Nitrite, nitric oxide and oxygen control respiratory flux at genetic and metabolic levels

The human pathogen Neisseria meningitidis is the major causative agent of bacterial meningitis. The organism is usually treated as a strict aerobe and is cultured under fully aerobic conditions in the laboratory. We demonstrate here that although N. meningitidis fails to grow under strictly anaerobic conditions, under oxygen limitation the bacterium expresses a denitrification pathway (reduction of nitrite to nitrous oxide via nitric oxide) and that this pathway supplements growth. The expression of the gene aniA, which encodes nitrite reductase, is regulated by oxygen depletion and nitrite availability via transcriptional regulator FNR and two-component sensor-regulator NarQ/NarP respectively. Completion of the two-step denitrification pathway requires nitric oxide (NO) reduction, which proceeds after NO has accumulated during batch growth under oxygen-limited conditions. During periods of NO accumulation both nitrite and NO reduction are observed aerobically, indicating N. meningitidis can act as an aerobic denitrifier. However, under steady-state conditions in which NO is maintained at a low concentration, oxygen respiration is favoured over denitrification. NO inhibits oxidase activity in N. meningitidis with an apparent Ki NO = 380 nM measured in intact cells. The high respiratory flux to nitrite after microaerobic growth and the finding that accumulation of the denitrification intermediate NO inhibits oxygen respiration support the view that denitrification is a pathway of major importance in N. meningitidis.

Evaluation of Recombinant Lipidated P2086 Protein as a Vaccine Candidate for Group B Neisseria meningitidis in a Murine Nasal Challenge Model

Neisseria meningitidis is a major causative agent of bacterial meningitis in human beings, especially among young children (</=2 years of age). Prevention of group B meningococcal disease represents a particularly difficult challenge in vaccine development, due to the inadequate immune response elicited against type B capsular polysaccharide. We have established an adult mouse intranasal challenge model for group B N. meningitidis to evaluate potential vaccine candidates through active immunization. Swiss Webster mice were inoculated intranasally with meningococci, and bacteria were recovered from the noses for at least 3 days postchallenge. Iron dextran was required in the bacterial inoculum to ensure sufficient meningococcal recovery from nasal tissue postchallenge. This model has been utilized to evaluate the potential of a recombinant lipidated group B meningococcal outer membrane protein P2086 (rLP2086) as a vaccine candidate. In this study, mice were immunized subcutaneously with purified rLP2086 formulated with or without an attenuated cholera toxin as an adjuvant. The mice were then challenged intranasally with N. meningitidis strain H355 or M982, and the colonization of nasal tissue was determined by quantitative culture 24 h postchallenge. We demonstrated that immunization with rLP2086 significantly reduced nasal colonization of mice challenged with the two different strains of group B N. meningitidis. Mice immunized with rLP2086 produced a strong systemic immunoglobulin G response, and the serum antibodies were cross-reactive with heterologous strains of group B N. meningitidis. The antibodies have functional activity against heterologous N. meningitidis strain, as demonstrated via bactericidal and infant rat protection assays. These results suggest that rLP2086 is a potential vaccine candidate for group B N. meningitidis.

Homology modelling of transferrin-binding protein A from Neisseria meningitidis

Neisseria meningitidis, a causative agent of bacterial meningitis, obtains transferrin-bound iron by expressing two outer membrane located transferrin-binding proteins, TbpA and TbpB. TbpA is thought to be an integral outer membrane pore that facilitates iron uptake. Evidence suggests that TbpA is a useful antigen for inclusion in a vaccine effective against meningococcal disease, hence the identification of regions involved in ligand binding is of paramount importance to design strategies to block uptake of iron. The protein shares sequence and functional similarities to the Escherichia coli siderophore receptors FepA and FhuA, whose structures have been determined. These receptors are composed of two domains, a 22-stranded beta-barrel and an N-terminal plug region that sits within the barrel and occludes the transmembrane pore. A three-dimensional TbpA model was constructed using FepA and FhuA structural templates, hydrophobicity analysis and homology modelling. TbpA was found to possess a similar architecture to the siderophore receptors. In addition to providing insights into the highly immunogenic nature of TbpA and allowing the prediction of potentially important ligand-binding epitopes, the model also reveals a narrow channel through its entire length. The relevance of this channel and the spatial arrangement of external loops, to the mechanism of iron translocation employed by TbpA is discussed.

Meningococcal Transferrin-Binding Proteins A and B Show Cooperation in Their Binding Kinetics for Human Transferrin

Neisseria meningitidis, a causative agent of bacterial meningitis and septicemia, obtains transferrin-bound iron by expressing two outer membrane-located transferrin-binding proteins, TbpA and TbpB. A novel system was developed to investigate the interaction between Tbps and human transferrin. Copurified TbpA-TbpB, recombined TbpA-TbpB, and individual TbpA and TbpB were reconstituted into liposomes and fused onto an HPA chip (BIAcore). All preparations formed stable monolayers, which, with the exception of TbpB, could be regenerated by removing bound transferrin. The ligand binding properties of these monolayers were characterized with surface plasmon resonance and shown to be specific for human transferrin. Kinetic data for diferric human transferrin binding showed that recombined TbpA-TbpB had K(a) and K(d) values similar to those of copurified TbpA-TbpB. Individual TbpA and TbpB also displayed K(a) values similar to those of copurified TbpA-TbpB, but their K(d) values were one order of magnitude higher. Chemical cross-linking studies revealed that TbpA and TbpB, in the absence of human transferrin, formed large complexes with TbpA as the predominant species. Upon human transferrin binding, a complex was formed with a molecular mass corresponding to that of a TbpB-human transferrin heterodimer as well as a higher-molecular-mass complex of this heterodimer cross-linked to TbpA. This indicates that TbpA and TbpB form a functional meningococcal receptor complex in which there is cooperativity in the human transferrin binding kinetics. However, iron loss from the diferric human transferrin-TbpA-TbpB complex was not greater than that from human transferrin alone, suggesting that additional meningococcal transport components are involved in the process of iron removal.

PCR of cerebrospinal fluid for diagnosis of bacterial meningitis during meningococcal epidemics; an example from Sudan.

Meningococcal disease is feared due to its rapid progression and high case fatality rate, especially in the African meningitis belt, where epidemics of meningococcal meningitis appear cyclically. Culture, direct microscopy and antigen detection are the basic methods for diagnosis and species identification of bacterial meningitis. These methods are known to have limitations, especially in developing countries. The aim of the present study was to document the application of PCR technology for the diagnosis of bacterial meningitis in cerebrospinal fluid (CSF) samples (n = 52) collected during epidemics in Sudan. In the application of PCR for detection of the causative agent of bacterial meningitis (based on the 16S rRNA gene), bacterial DNA was identified in 49 samples. Common bacterial species causing bacterial meningitis could be detected in 31 of the CSF samples (27 meningococci), while 18 contained DNA, mainly from normally contaminating bacteria. A specific PCR for group A meningococci (based on the sacC gene) was positive in 27 of the CSF samples. The results show that PCR technology is a sharp-edged tool for confirmation of a diagnosis of meningococcal meningitis and for obtaining a direct genogrouping of group A meningococci in CSF. It is important to stress the use of direct and specific PCRs to avoid interference by contaminating bacteria, a great problem in samples from areas in the meningitis belt.

Interactions of Haemophilus influenzae with human endothelial cells in vitro.

Journal Article Interactions of Haemophilus influenzae with Human Endothelial Cells In Vitro Get access Mumtaz Virji, Mumtaz Virji Molecular Infectious Diseases Group, Department of Paediatrics, and Nuffield Department of Pathology, John Radcliffe Hospital, Search for other works by this author on: Oxford Academic PubMed Google Scholar Helena Käyhty, Helena Käyhty Molecular Infectious Diseases Group, Department of Paediatrics, and Nuffield Department of Pathology, John Radcliffe Hospital, Search for other works by this author on: Oxford Academic PubMed Google Scholar David J. P. Ferguson, David J. P. Ferguson Molecular Infectious Diseases Group, Department of Paediatrics, and Nuffield Department of Pathology, John Radcliffe Hospital, Search for other works by this author on: Oxford Academic PubMed Google Scholar Carol Alexandrescu, Carol Alexandrescu Molecular Infectious Diseases Group, Department of Paediatrics, and Nuffield Department of Pathology, John Radcliffe Hospital, Search for other works by this author on: Oxford Academic PubMed Google Scholar E. Richard Moxon E. Richard Moxon Molecular Infectious Diseases Group, Department of Paediatrics, and Nuffield Department of Pathology, John Radcliffe Hospital, Search for other works by this author on: Oxford Academic PubMed Google Scholar The Journal of Infectious Diseases, Volume 165, Issue Supplement_1, June 1992, Pages S115–S116, https://doi.org/10.1093/infdis/165-Supplement_1-S115 Published: 01 June 1992

Rapid differentiation of the major causative agents of bacterial meningitis by use of frequency-pulsed electron capture gas-liquid chromatography: analysis of amines.

The major causative agents of bacterial meningitis (Haemophilus influenzae serogroup B, Neisseria meningitidis serogroups B and C, Klebsiella pneumoniae, Steptococcus pneumoniae, and two types of Escherichia coli) were cultured in a chemically defined medium, and selected strains were further studied in Todd-Hewitt medium. After acidic extraction of the spent media with chloroform, a basic extraction was made with chloroform to obtain amines. A third extraction was performed on re-acidified Todd-Hewitt medium with ethyl ether to obtain hydroxyacids. The extracts were derivatized with heptafluorobutyric anhydride-ethanol to form electron-capturing derivatives, and the derivatives were analyzed on a frequency-pulsed electron capture gas-liquid chromatograph (FPEC-GLC) equipped with a PEP-2 computer. The data obtained from the study showed that amines were produced by these organisms that formed characteristic patterns. Different serotypes of K. pneumoniae and the two serogroups of N. meningitidis produced different types of FPEC-GLC profiles within serotypes. E. coli produced several hydroxy acids on Todd-Hewitt medium that made it unique among the organisms studied. The methods used are practical and the techniques have potential for use in clinical laboratories and hospitals as a valuable aid for the rapid identification of the major causative agents of bacterial meningitis.

Rapid differentiation of the major causative agents of bacterial meningitis by use of frequency-pulsed electron capture gas-liquid chromatograph: analysis of acids.

The major causative agents of bacterial meningitis, Haemophilus influenzae serogroup B, Neisseria meningitidis serogroups B and C, Klebsiella pneumoniae, Streptococcus pneumoniae, and two types of Escherichia coli, were cultured in a modified chemically defined Catlin medium and in a commercial version of the unmodified Catlin medium. The spent media were extracted under acidic conditions, and electron-capturing derivatives were prepared by derivatization with trichloroethanol or haptafluorobutyric anhydride. The derivatives were analyzed on a gas chromatograph equipped with a frequency-pulsed electron capture detector and a PEP-2 computer. The data obtained from the study show that these organisms can be easily distinguished from each other on the basis of metabolic products detected in either type of medium. Three different metabolic groups were detected within two serogroups of N. meningitidis. The methods are practical, and the new technique should offer clinical laboratories and hospitals a better method for rapid identification of this important group of pathogens.

Practical considerations in using counterimmunoelectrophoresis to identify the principal causative agents of bacterial meningitis.

Many clinical laboratories are currently using counterimmunoelectrophoresis (CIE) as an aid in the rapid diagnosis of bacterial meningitis. Because cross-reactions among causative agents have been reported, the present study was undertaken to explore the problems that might occur when reference and commercial antisera are used in CIE. Broth cultures of 35 bacterial strains were tested with 76 reference and commercial antisera by CIE. Some of the antisera tested failed to react with their homologous strains. Furthermore, several cross-reactions between genera, as well as within species, were noted. These findings suggest that precautions must be taken to insure that all materials used in CIE tests are of high quality. If properly performed and interpreted, CIE may be a valuable adjunct in the identification of organisms causing bacterial meningitis, but it is, nevertheless, a presumptive test and should not be used to replace the Gram stain and culture techniques.