Emergence of new virulent Neisseria meningitidis serogroup C sequence type 11 isolates in France.

In France, there have been variations in the incidence of invasive meningococcal infection due to serogroup C isolates. Infection peaks were observed in 1992 and 2003 that involved isolates of phenotypes C:2a:P1.5,2 and/or C:2a:P1.5, which belong to the sequence type 11 (ST-11) clonal complex. We report an emergence of isolates belonging to the ST-11 clonal complex since 2003. These isolates displayed a new phenotype, C:2a:P1.7,1, caused infections that occurred as clusters, and were associated with increased infection severity and high virulence in mice. These isolates may be responsible for a peak in the incidence of serogroup C meningococcal infection in France, for which there is no routine vaccination to date.

Association of meningococcal phenotypes and genotypes with clinical characteristics and mortality of meningitis in children.

BACKGROUND: Neisseria meningitidis meningitis represents approximately one-half of the meningococcal cases in French children. To explore the contribution of bacterial typing in improving the management of cases, we aimed to describe clinical characteristics and mortality of meningococcal meningitis in children reported to the multicenter survey system, GPIP/ACTIV, in association with phenotypes/genotypes of bacterial isolates. METHODS: From 2001 to 2005, 259 pediatric wards and 168 microbiology laboratories enrolled all children with bacterial meningitis. Risk factors, vaccination status, signs and symptoms, cerebrospinal fluid analysis, treatments and case fatality rate were recorded. RESULTS: A total of 962 cases of Neisseria meningitidis meningitis among a total of 2131 bacterial meningitis (45%) were recorded (mean age, 4.5 +/- 4.7 years). Serogroup distribution of the isolates was 62.3%, 33.7%, 2.9%, 0.6%, and 0.6% for serogroups B, C, W135, A and Y, respectively. The major clonal complexes were ST-41/44 (32.2%), ST-11 (21.9%), ST-32 (20.8%), ST-8 (8.2%), and ST-269 (4.9%). Despite global heterogeneity of the isolates, 2 phenotypes/genotypes were of interest. Isolates of the phenotype/genotype B:14:P1.7,16/ST-32 (56% clustered in the region of Haute Normandie) were observed in older children (8.6 years) and were associated with a higher case fatality rate (12%) than were other phenotypes of serogroup B. The phenotype/genotype C:2a:P1.5/ST-11 was found in 26.3% of serogroup C cases and was possibly associated with a higher mortality among serogroup C (9.9% for C and 5.9% for B, P = 0.04). CONCLUSIONS: This large survey provides data that could be important for implementation of future vaccines. Typing of meningococcal isolates could contribute to an understanding of prognosis in meningococcal meningitis.

Emerging drugs for acute bacterial meningitis.

The management of acute bacterial meningitis is based on early antibiotic treatment to prevent unfavorable outcome (death and permanent sequelae). beta-Lactam antibiotics, particularly third-generation cephalosporins, are effective against most agents of community-acquired acute bacterial meningitis. Resistance to beta-lactams evolves, particularly in Streptococcus pneumoniae, that may lead to treatment failure. Evaluation of other antibiotics such as fourth-generation cephalosporin, new penems and quinolones is warranted. Adjunctive therapy aims to reduce tissue injuries provoked by the inflammatory response. The use of dexamethasone is still a matter of debate, but seems to be helpful under conditions of rapid etiological diagnosis and prompt management. Other drugs that neutralize bacterial factors or host mechanisms involved in induction of inflammatory response are under development.

Influenza A virus neuraminidase enhances meningococcal adhesion to epithelial cells through interaction with sialic acid-containing meningococcal capsules.

The underlying mechanisms of the epidemiological association between influenza virus infections and Neisseria meningitidis invasive infections are not fully understood. Here we report that adhesion of N. meningitidis to human Hec-1-B epithelial cells is enhanced by influenza A virus (IAV) infection. A potential role of the viral neuraminidase (NA) in facilitating meningococcal adhesion to influenza virus-infected epithelial cells was examined. Expression of a recombinant IAV NA in Hec-1-B human epithelial cells increased the adhesion of strains of N. meningitidis belonging to the sialic acid-containing capsular serogroups B, C, and W135 but not to the mannosamine phosphate-containing capsular serogroup A. Adhesion enhancement was not observed with an inactive NA mutant or in the presence of an NA inhibitor (zanamivir). Furthermore, purified IAV NA was shown to cleave sialic acid-containing capsular polysaccharides of N. meningitidis. On the whole, our findings suggest that a direct interaction between the NA of IAV and the capsule of N. meningitidis enhances bacterial adhesion to cultured epithelial cells, most likely through cleavage of capsular sialic acid-containing polysaccharides. A better understanding of the association between IAV and invasive meningococcal infections should help to set up improved control strategies against these seasonal dual viral-bacterial infections.

[Anti-meningococcal vaccines]. / Vaccins antiméningococciques.

Current anti-meningococcal vaccines are prepared from capsular saccharides (plain or conjugate). They target four serogroups A, C, Y and W135. No vaccine is available against serogroup B saccharide. However, protein-based vaccines (recombinant vaccines or outer membrane vesicle vaccines) allow developing vaccines against serogroup B isolates.

Transgenic mice expressing human transferrin as a model for meningococcal infection.

The pathogenesis of meningococcal disease is poorly understood due to the lack of a relevant animal model. Moreover, the use of animal models is not optimal as most meningococcal virulence determinants recognize receptors that are specifically expressed in human tissues. One major element of the host specificity is the system of meningococcal iron uptake by transferrin-binding proteins that bind specifically human transferrin but not murine transferrin. We developed a new mouse model for experimental meningococcal infection using transgenic mice expressing human transferrin. Intraperitoneal challenge of transgenic mice induced bacteremia for at least 48 h with an early stage of multiplication, whereas the initial inoculum was rapidly cleared from blood in wild-type mice. Inflammation in the subarachnoidal space with a high influx of polymorphonuclear cells was observed only in transgenic mice. Meningococcal mutants that were unable to use transferrin as a source of iron were rapidly cleared from both wild-type and transgenic mice. Thus, transgenic mice expressing human transferrin may represent an important advance as a new mouse model for in vivo studies of meningococcal virulence and immunogenicity factors.

Meningococcal vaccines: to eradicate the disease, not the bacterium.

Neisseria meningitidis is exclusively a human-adapted bacterium, most frequently found in asymptomatic carriage that promotes natural immunity. However, it is also the causative agent of severe invasive infections, such as septicaemia and/or meningitis that may lead to life-threatening septic shock. Vaccination with capsular polysaccharidic antigens (either plain or conjugated) induces serogroup specific protective antibodies. Meningococcal capsular polysaccharide vaccines are only available against serogroups A, C, Y and W135. There is no available capsular vaccine against serogroup B. Future strategies to develop meningococcal vaccine should be global strategies aimed to design a "universal vaccine" effective against meningococcal disease due to any strain, regardless its phenotype and genotype. However, these global strategies may be hindered by the high diversity of meningococcal isolates and their changing epidemiology. Alternatively, targeted or local vaccine strategies may be developed against specific isolates and can help particularly in controlling outbreaks while preserving benefits from carriage.

Workshop on vaccine pressure and Neisseria meningitidis, Annecy, France, 9-11 March 2005.

A 3-day workshop, "Vaccine pressure and Neisseria meningitidis", was held in Annecy, France, 9-11 March 2005, to summarize the current state of knowledge regarding N. meningitidis capsule switching and vaccine pressure from capsular polysaccharide-based N. meningitidis vaccines, including conjugates. Main discussion topics were the host-bacteria relationship and N. meningitidis population, worldwide experience of meningococcal vaccination, and using existing experience to shape the future of meningococcal vaccination strategies. The workshop concluded that there is no current evidence to suggest that serogroup C conjugate vaccine pressure has resulted in meningococcal serogroup switching or replacement.

Susceptibility of Neisseria gonorrhoeae to antimicrobial peptides from amphibian skin, dermaseptin, and derivatives.

We evaluated the antimicrobial effect of antimicrobial peptides from frog skin belonging to the dermaseptin family against reference and clinical Neisseria gonorrhoeae strains, including penicillin-resistant strains. Dermaseptin S4 exhibited anti-N. gonorrhoeae activity against all strains with MICs ranging between 10 and 100 microg/mL. We then used derivatives of DS4 and determined the anti-N. gonorrhoeae activity of each of analogs. All the derivatives showed antimicrobial activity. Among the different molecules tested, we found that dermaseptins K4S4 (1-16)a and K4S4 (1-28) were the more potent to inhibit N. gonorrhoeae growth with MIC of 10 microg/mL against all strains.

Differential role of lipooligosaccharide of Neisseria meningitidis in virulence and inflammatory response during respiratory infection in mice.

Meningococcal lipooligosaccharide (LOS) induces a strong proinflammatory response in humans during meningococcal infection. We analyzed the role of LOS in the inflammatory response and virulence during the early infectious process in a mouse model of meningococcal respiratory challenge. An lpxA mutant strain (serogroup B) devoid of LOS (strain Z0204) could not persist in the lungs and did not invade the blood. The persistence in the lungs and invasion of the bloodstream by a rfaD mutant expressing truncated LOS with only lipid A and 3-deoxy-d-manno-2-octulosonic acid molecules (strain Z0401) was intermediate between those of the wild-type and Z0204 strains. Both LOS mutants induced acute pneumonia with the presence of infiltrating polymorphonuclear leukocytes in lungs. Although tumor necrosis factor alpha production was reduced in mice infected with the mutant of devoid LOS, both LOS mutants induced production of other proinflammatory cytokines, such as interleukin-1beta (IL-1beta), IL-6, and the murine IL-8 homolog KC. Together, these results suggest that meningococcal LOS plays a role during the early infectious and invasive process, and they further confirm that other, nonlipopolysaccharide components of Neisseria meningitidis may significantly contribute to the inflammatory reaction of the host.

The rise and fall of epidemic Neisseria meningitidis serogroup W135 meningitis in Burkina Faso, 2002-2005.

BACKGROUND: During the period 2001-2002, Burkina Faso reported its first meningitis epidemic due to Neisseria meningitidis (Nm) serogroup W135, prompting concerns that this serogroup would persist as a cause of epidemic disease. METHODS: During the period 2002-2005, hospital- and population-based surveillances were conducted in 3 districts in Burkina Faso. Etiology was determined by culture, polymerase chain reaction (PCR), and latex agglutination. Reference laboratories determined phenotype and genotype. RESULTS: Of 2004 subjects who received a lumbar puncture, 265 were identified as having Nm, including 93 who had Nm serogroup A (NmA) and 146 who had Nm serogroup W135 (NmW135). Over the study period, the proportion of cases due to NmW135 decreased by >75%, primarily because of decreased occurrence among young children and in a single district. During peak epidemic months, the annualized incidence of NmW135 decreased from 146 cases to <1 case per 100,000 population. All but 2 NmW135 isolates were phenotype W135:2a:P1.5,2 (sequence type [ST]-11 clonal complex). All NmA isolates were phenotype A:4:P1-9 (ST-2859 of the ST-5 clonal complex). We identified 1 isolate from serogroup Y (ST-11 clonal complex), 1 isolate from serogroup X that was similar to strains previously associated with epidemic disease, and 1 isolate from serogroup W135 of the newly described ST-4375 complex. CONCLUSIONS: For unknown reasons, serogroup W135 achieved epidemic status, primarily among young children, and then largely disappeared over a short time period. The continued circulation of multiple strains with epidemic potential emphasizes the need for ongoing surveillance and the potential benefit of vaccines that are protective across serogroups.

Immunogenicity of meningococcal PBP2 during natural infection and protective activity of anti-PBP2 antibodies against meningococcal bacteraemia in mice.

OBJECTIVE: To evaluate the immunogenicity of the meningococcal penicillin-binding protein 2 (PBP2) and its potential as a vaccine candidate. METHODS: The immunogenicity of meningococcal PBP2 was investigated using acute and convalescent sera from patients who recovered from meningococcal disease. Sera were tested against purified recombinant PBP2s corresponding to meningococcal isolates of different genetic lineages, of different serogroups and with various susceptibility levels to penicillin G. Mice were vaccinated with recombinant PBP2 and challenged with Neisseria meningitidis. A purified anti-PBP2 rabbit IgG was also used for passive protection experiments in mice. RESULTS: Convalescent patients' sera recognized PBP2s from different strains, showing that this protein is immunogenic in meningococcal disease. Vaccination with purified recombinant PBP2 and purified anti-PBP2 rabbit IgG antibody conferred protection against experimental meningococcaemia in mice. CONCLUSION: These data argue for considering meningococcal PBP2 as a vaccine candidate.

Conserved virulence of C to B capsule switched Neisseria meningitidis clinical isolates belonging to ET-37/ST-11 clonal complex.

Capsule switching in Neisseria meningitidis is thought to occur by horizontal DNA exchange between meningococcal strains. Antigenic variants may be generated by allelic replacement of the siaD gene; the variants may then be selected by specific immunity against the capsular antigen. There were several vaccination campaigns against serogroup C in France in 2002, following an increase in the prevalence of invasive isolates of serogroup C of the phenotype C:2a:P1.5 and C:2a:P1.5,2 belonging to the ET-37/ST-11 clonal complex. We evaluated the emergence of capsule variants by the detection of B:2a:P1.5 and B:2a:P1.5,2 meningococcal isolates of the ET-37/ST-11 clonal complex. These isolates were significantly more frequent after the year 2002. Pulsed field gel electrophoresis profiles of the serogroup B (ET-37/ST-11) isolates differed from that of serogroup C (ET-37/ST-11) isolates by the bands that harbor the siaD genes responsible for the serogroup specificity. However, serogroup B and C, ET37/ST-11 isolates both express similar virulence as assessed from colonization and invasiveness in a mouse model. Our results indicate that capsule switching events within the same clonal complex can arise frequently with no alteration in virulence. This justifies an enhanced system of surveillance by molecular typing of such isolates, particularly after serogroup-specific vaccination.

Bacterial meningitis in children: a French prospective study.

From January 2001 through December 2003, a total of 1084 children with bacterial meningitis were enrolled in a prospective French nationwide survey. The most frequent pathogens found in children older than 28 days were Neisseria meningitis (55.3%) and Streptococcus pneumoniae (33.4%). S. pneumoniae was the most frequent pathogen found among infants aged 2-12 months (49.5%), whereas N. meningitidis was the most frequent pathogen among children >12 months old (69.7%). Approximately one-half of S. pneumoniae isolates had diminished susceptibility to penicillin. The case-fatality rates were 7.6% for children with N. meningitidis meningitis and 10.8% for children with S. pneumoniae infection.