Ulrich Vogel

Genetic analysis of meningococci carried by children and young adults

BACKGROUND Neisseria meningitidis is a diverse commensal bacterium that occasionally causes severe invasive disease. The relationship between meningococcal genotype and capsular polysaccharide, the principal virulence factor and vaccine component, was investigated in carried meningococci isolated from 8000 children and young adults in Bavaria, Germany. METHODS Of the 830 meningococci isolated (carriage rate, 10.4%) by microbiological techniques, 822 were characterized by serogrouping, multilocus sequence typing, and genetic analysis of the capsule region. Statistical and population genetic analyses were applied to these data. RESULTS The rapid increase in carriage rates with age of carrier, the low prevalence of hyperinvasive meningococci, and the relative prevalence of the 4 disease-associated serogroups were consistent with earlier observations. There was no genetic structuring of the meningococcal population by age of carrier or sampling location; however, there was significant geographic structuring of the meningococci isolated in civil, but not military, institutions. The rate of capsule gene expression did not vary with age of carrier or meningococcal genotype, except for serogroup C, for which increased expression was associated with ST-11 (formerly ET-37) complex meningococci. CONCLUSIONS Serogroup C capsule expression during carriage may contribute to the invasive character of ST-11 complex meningococci and to the high efficacy of meningococcal serogroup C conjugate polysaccharide vaccine.

Binding of the Complement Inhibitor C4bp to Serogroup B Neisseria meningitidis

Neisseria meningitidis (meningococcus) is an important cause of meningitis and sepsis. Currently, there is no effective vaccine against serogroup B meningococcal infection. Host defense against neisseriae requires the complement system (C) as indicated by the fact that individuals deficient in properdin or late C components (C6-9) have an increased susceptibility to recurrent neisserial infections. Because the classical pathway (CP) is required to initiate efficient complement activation on neisseriae, meningococci should be able to evade it to cause disease. To test this hypothesis, we studied the interactions of meningococci with the major CP inhibitor C4b-binding protein (C4bp). We tested C4bp binding to wild-type group B meningococcus strain (H44/76) and to 11 isogenic mutants thereof that differed in capsule expression, lipo-oligosaccharide sialylation, and/or expression of either porin (Por) A or PorB3. All strains expressing PorA bound radiolabeled C4bp, whereas the strains lacking PorA bound significantly less C4bp. Increased binding was observed under hypotonic conditions. Deleting PorB3 did not influence C4bp binding, but the presence of polysialic acid capsule reduced C4bp binding by 50%. Bound C4bp remained functionally active in that it promoted the inactivation of C4b by factor I. PorA-expressing strains were also more resistant to C lysis than PorA-negative strains in a serum bactericidal assay. Binding of C4bp thus helps Neisseria meningitidis to escape CP complement activation.

Genetics of capsule O‐acetylation in serogroup C, W‐135 and Y meningococci

Capsular polysaccharides of serogroup C, W‐135 and Y meningococci were previously reported to be O‐acetylated at the sialic acid residues. There is evidence that O‐acetylation affects the immunogenicity of polysaccharide vaccines. We identified genes indispensable for O‐acetylation of serogroup C, W‐135 and Y meningococci downstream of the capsule synthesis genes siaA–D. The genes were co‐transcribed with the sia operon as shown by reverse transcription polymerase chain reaction analysis. The putative capsular polysaccharide O‐acetyltransferases were designated OatC and OatWY. The protein OatWY of serogroups W‐135 and Y showed sequence homologies to members of the NodL–LacA–CysE family of bacterial acetyltransferases, whereas no sequence homology with any known protein in the different databases was found for the serogroup C protein OatC. In serogroup W‐135 and Y meningococci, several clonal lineages either lacked OatWY or OatWY was inactivated by insertion of IS1301. For serogroup C meningococci, we observed in vitro phase variation of O‐acetylation, which resulted from slipped‐strand mispairing in homopolymeric tracts. This finding explains the observation of naturally occurring de‐O‐acetylated serogroup C meningococci. Our report is the first description of sequences of sialic acid O‐acetyltransferase genes that have not been cloned from either other bacterial or mammalian organisms.

Interlaboratory Comparison of PCR-Based Identification and Genogrouping of Neisseria meningitidis

ABSTRACT Twenty clinical samples (18 cerebrospinal fluid samples and 2 articular fluid samples) were sent to 11 meningococcus reference centers located in 11 different countries. Ten of these laboratories are participating in the EU-MenNet program (a European Union-funded program) and are members of the European Monitoring Group on Meningococci. The remaining laboratory was located in Burkina Faso. Neisseria meningitidis was sought by detecting several meningococcus-specific genes (crgA, ctrA, 16S rRNA, and porA). The PCR-based nonculture method for the detection of N. meningitidis gave similar results between participants with a mean sensitivity and specificity of 89.7 and 92.7%, respectively. Most of the laboratories also performed genogrouping assays (siaD and mynB/sacC). The performance of genogrouping was more variable between laboratories, with a mean sensitivity of 72.7%. Genogroup B gave the best correlation between participants, as all laboratories routinely perform this PCR. The results for genogroups A and W135 were less similar between the eight participating laboratories that performed these PCRs.

Carbohydrate composition of meningococcal lipopolysaccharide modulates the interaction of Neisseria meningitidis with human dendritic cells

Meningococcal lipopolysaccharide (LPS) is of crucial importance for the pathogenesis of invasive infection. We show that sialylation and elongation of the alpha‐chain effectively shields viable unencapsulated Neisseria meningitidis from recognition by human dendritic cells (DC). In contrast, beta‐ and gamma‐ chain of the LPS carbohydrate moiety play only a minor role in the interaction with DC. The protective function of the LPS for the bacteria can be counteracted in vivo by phase variation of the lgtA gene encoding LPS glycosyltransferase A. Capsule expression protects N. meningitidis efficiently from recognition and phagocytosis by DC independent of the LPS structure. Despite the significant impact of LPS composition on the adhesion and phagocytosis of N. meningitidis no differences were found in terms of cytokine levels secreted by DC for IL1‐beta, IL‐6, IL‐8, TNF‐alpha, IFN‐gamma and GM‐CSF. However, significantly lower levels of the regulatory mediator IL‐10 were induced by encapsulated strains in comparison to isogenic unencapsulated derivatives. IL‐10 secretion was shown to depend on phagocytosis because poly alpha‐2,8 sialic acid did not influence IL‐10 secretion. The use of truncated LPS isoforms in vaccine preparations can therefore not only result in attenuation but also in more efficient targeting of DC.

Epidemiologie invasiver Infektionen durch Neisseria meningitidis

ZusammenfassungDer Mensch ist einziges Reservoir der Meningokokken. Der Erreger zeichnet sich durch eine hohe genetische und antigenetische Variabilität aus. Bisher wurden 25 genetische Linien und über 3000 so genannte Sequenztypen beschrieben, jedoch ist nur ein geringer Teil der den Menschen besiedelnden genetischen Linien als pathogen einzustufen. Die Besiedlung mit Meningokokken induziert eine klonspezifischen Immunität. Die klonale Verbreitung einer Meningokokkenvariante führt zur Herdimmunität und trägt zum Wechsel der endemischen oder epidemischen Klone bei. Die Mehrzahl invasiver Meningokokkeninfektionen tritt sporadisch auf, Cluster werden jedoch regelmäßig beobachtet. Übertragungen der Infektion im Krankenhaus sind überaus selten. Im afrikanischen Meningitisgürtel werden regelmäßig große Ausbrüche beobachtet. Reise- und Impfberatungen müssen sich an den aktuellen epidemiologischen Entwicklungen orientieren.AbstractNeisseria meningitidis (a meningococcus) colonises the human nasopharynx. This pathogen is characterised by a high level of genetic and antigenetic variability. So far, 25 clonal lineages and more than 3,000 sequence types have been described, but only a few of these have pathogenic potential for humans. Strain-specific immunity is induced by colonisation with meningococci. Furthermore, herd immunity is observed after clonal spread of a strain within a human population. Herd immunity is responsible for changes in endemic or epidemic lineages. Most cases of meningococcal infection must be regarded as sporadic; nosocomial infections are rare, but clusters are observed on a regular basis in communities. The African meningitis belt regularly sees widespread and sometimes devastating epidemics. Recommendations on travel and vaccination must be made with due consideration for the current epidemiological developments in meningococcal disease at the time of any consultation.