Increased genetic diversity of Neisseria meningitidis isolates after the introduction of meningococcal serogroup C polysaccharide conjugate vaccines

An In Silico Analysis of Malaria Pre-Erythrocytic-Stage Antigens Interpreting Worldwide Genetic Data to Suggest Vaccine Candidate Variants and Epitopes

Failure to account for genetic diversity of antigens during vaccine design may lead to vaccine escape. To evaluate the vaccine escape potential of antigens used in vaccines currently in development or clinical testing, we surveyed the genetic diversity, measured population differentiation, and performed in silico prediction and analysis of T-cell epitopes of ten such Plasmodium falciparum pre-erythrocytic-stage antigens using whole-genome sequence data from 1010 field isolates. Of these, 699 were collected in Africa (Burkina Faso, Cameroon, Guinea, Kenya, Malawi, Mali, and Tanzania), 69 in South America (Brazil, Colombia, French Guiana, and Peru), 59 in Oceania (Papua New Guinea), and 183 in Asia (Cambodia, Myanmar, and Thailand). Antigens surveyed include cell-traversal protein for ookinetes and sporozoites, circumsporozoite protein, liver-stage antigens 1 and 3, sporozoite surface proteins P36 and P52, sporozoite asparagine-rich protein-1, sporozoite microneme protein essential for cell traversal-2, and upregulated-in-infectious-sporozoite 3 and 4 proteins. The analyses showed that a limited number of these protein variants, when combined, would be representative of worldwide parasite populations. Moreover, predicted T-cell epitopes were identified that could be further explored for immunogenicity and protective efficacy. Findings can inform the rational design of a multivalent malaria vaccine.

Lung abscess due to Neisseria meningitidis serogroup X-unexpected virulence of a commensal resulting from putative serogroup B capsular switching

To report the first case of a lung abscess caused by Neisseria meningitidis (Nm) and to genetically characterize the rare underlying capsule switching event. The strain (PT NmX) was subjected to whole genome sequencing, and a comparative gene-by-gene analysis was performed based on 1605 N. meningitidis core loci that constitute the MLST core-genome scheme (cgMLST) V1.0. All ~ 9,600 genomes available on Neisseria PubMLST (until 30th November 2019) from all serogroups were used to better identify the genome make-up of the PT NmX strain. This strain was found to be highly divergent from other NmX reported worldwide and to belong to a new sequence type (ST-14273), with the finetype X: P1.19,15-1:F5-2. Moreover, it revealed a closer genetic proximity to strains from serogroup B than to other serogroups, suggesting a genome backbone associated with serogroup B, while it presents a capsule synthesis region derived from a NmX strain. We describe a new hybrid NmB/X isolate from a noninvasive meningococcal infection, causing lung abscess. Despite capsular switching events involving serogroup X are rare, it may lead to the emergence of pathogenic potential. Studies should continue to better understand the molecular basis underlying Neisseria strains' ability to spread to body compartments other than the tissues for which their tropism is already known.

Capsule switching of Neisseria meningitidis sequence type 7 serogroup A to serogroup X

OBJECTIVES

The bacterial pathogen Neisseria meningitidis is able to escape the currently available capsule-based vaccines by undergoing capsule switching. In this study, we investigated whether capsule switching has occurred in a recently emerged sequence type (ST) 7 serogroup X isolate in China, for which currently no vaccine is available.

METHODS

To identify capsule switching breakpoints, the capsule locus and flanking regions of the ST-7 serogroup X isolate and three endemic ST-7 serogroup A isolates were sequenced and compared. To obtain further insight into capsule switching frequency and length of DNA fragments involved, capsule switching assays were performed using genomic DNA containing combinations of antibiotic selection markers at various locations in the capsule locus and flanking regions.

RESULTS

Sequence analyses showed that capsule switching has occurred and involved a 8450 bp serogroup X DNA fragment spanning the region from galE to ctrC. Capsule switching assays indicate that capsule switching occurs at a frequency of 6.3 × 10^-6 per bacterium per μg of DNA and predominantly involved DNA fragments of about 8.1-9.6 kb in length.

CONCLUSIONS

Our results show that capsule switching in N. meningitidis occurs at high frequency and involves recombination in the flanking regions of the capsule biosynthesis genes.

Genomic Landscape of Intrahost Variation in Group A Streptococcus: Repeated and Abundant Mutational Inactivation of the fabT Gene Encoding a Regulator of Fatty Acid Synthesis

To obtain new information about Streptococcus pyogenes intrahost genetic variation during invasive infection, we sequenced the genomes of 2,954 serotype M1 strains recovered from a nonhuman primate experimental model of necrotizing fasciitis. A total of 644 strains (21.8%) acquired polymorphisms relative to the input parental strain. The fabT gene, encoding a transcriptional regulator of fatty acid biosynthesis genes, contained 54.5% of these changes. The great majority of polymorphisms were predicted to deleteriously alter FabT function. Transcriptome-sequencing (RNA-seq) analysis of a wild-type strain and an isogenic fabT deletion mutant strain found that between 3.7 and 28.5% of the S. pyogenes transcripts were differentially expressed, depending on the growth temperature (35°C or 40°C) and growth phase (mid-exponential or stationary phase). Genes implicated in fatty acid synthesis and lipid metabolism were significantly upregulated in the fabT deletion mutant strain. FabT also directly or indirectly regulated central carbon metabolism genes, including pyruvate hub enzymes and fermentation pathways and virulence genes. Deletion of fabT decreased virulence in a nonhuman primate model of necrotizing fasciitis. In addition, the fabT deletion strain had significantly decreased survival in human whole blood and during phagocytic interaction with polymorphonuclear leukocytes ex vivo We conclude that FabT mutant progeny arise during infection, constitute a metabolically distinct subpopulation, and are less virulent in the experimental models used here.

Designing malaria vaccines to circumvent antigen variability

Prospects for malaria eradication will be greatly enhanced by an effective vaccine, but parasite genetic diversity poses a major impediment to malaria vaccine efficacy. In recent pre-clinical and field trials, vaccines based on polymorphic Plasmodium falciparum antigens have shown efficacy only against homologous strains, raising the specter of allele-specific immunity such as that which plagues vaccines against influenza and HIV. The most advanced malaria vaccine, RTS,S, targets relatively conserved epitopes on the P. falciparum circumsporozoite protein. After more than 40 years of development and testing, RTS,S, has shown significant but modest efficacy against clinical malaria in phase 2 and 3 trials. Ongoing phase 2 studies of an irradiated sporozoite vaccine will ascertain whether the full protection against homologous experimental malaria challenge conferred by high doses of a whole organism vaccine can provide protection against diverse strains in the field. Here we review and evaluate approaches being taken to design broadly cross-protective malaria vaccines.

Clonal analysis of meningococci during a 26 year period prior to the introduction of meningococcal serogroup C vaccines

Meningococcal disease remains a public health burden in the UK and elsewhere. Invasive Neisseria meningitidis, isolated in Scotland between 1972 and 1998, were characterised retrospectively to examine the serogroup and clonal structure of the circulating population. 2607 isolates causing invasive disease were available for serogroup and MLST analysis whilst 2517 were available for multilocus sequence typing (MLST) analysis only. Serogroup distribution changed from year to year but serogroups B and C were dominant throughout. Serogroup B was dominant throughout the 1970s and early 1980s until serogroup C became dominant during the mid-1980s. The increase in serogroup C was not associated with one particular sequence type (ST) but was associated with a number of STs, including ST-8, ST-11, ST-206 and ST-334. This is in contrast to the increase in serogroup C disease seen in the 1990s that was due to expansion of the ST-11 clonal complex. While there was considerable diversity among the isolates (309 different STs among the 2607 isolates), a large proportion of isolates (59.9%) were associated with only 10 STs. These data highlight meningococcal diversity over time and the need for ongoing surveillance during the introduction of new meningococcal vaccines.

Meningococcal serogroup W135 in the African meningitis belt: epidemiology, immunity and vaccines

In the sub-Saharan African meningitis belt there is a region of hyperendemic and epidemic meningitis stretching from Senegal to Ethiopia. The public health approaches to meningitis epidemics, including those related to vaccine use, have assumed that Neisseria meningitidis serogroup A will cause the most disease. During 2001 and 2002, the first large-scale epidemics of serogroup W135 meningitis in sub-Saharan Africa were reported from Burkina Faso. The occurrence of N. meningitidis W135 epidemics has led to a host of new issues, including the need for improved laboratory diagnostics for identifying serogroups during epidemics, an affordable supply of serogroup W135-containing polysaccharide vaccine for epidemic control where needed, and re-evaluating the long-term strategy of developing a monovalent A conjugate vaccine for the region. This review summarizes the existing data on N. meningitidis W135 epidemiology, immunology and vaccines as they relate to meningitis in sub-Saharan Africa.

Molecular methods for the detection and characterization ofNeisseria meningitidis

Neisseria meningitidis remains a common global cause of morbidity and mortality. The laboratory confirmation of meningococcal disease is, therefore, very important for individual patient management and for public health management. Through surveillance schemes, it provides long-term epidemiologic data that can be used to inform vaccine policy. Traditional methods, such as latex agglutination and the enzyme-linked immunosorbent assay, are still used, but molecular methods are now also established. In this review, molecular methods for the laboratory confirmation and characterization of meningococci are described. PCR is an invaluable tool in modern biology and can be used to predict the group, type and subtype of meningococci. It is now also used in a fluorescence-based format for increased sensitivity and specificity. The method also provides the amplified DNA for other techniques, such as multilocus sequence typing. Other methods for the discrimination of meningococci have also played and continue to play an important part in epidemiology. For example, pulsed-field gel electrophoresis is highly discriminatory, whilst multilocus enzyme electrophoresis provided the basis for the description of global meningococcal clones and formed the foundation for multilocus sequence typing. Other less commonly used methods, such as matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and pyrosequencing, may increasingly find their way into microbiology reference laboratories. Nevertheless, nucleotide sequencing and laboratory automation have aided the introduction of many methods and provide data that are digitally based and, therefore, highly accurate and portable.

The changing epidemiology of meningococcal disease in Quebec, Canada, 1991-2011: potential implications of emergence of new strains

Background

In order to inform meningococcal disease prevention strategies, we analysed the epidemiology of invasive meningococcal disease (IMD) in the province of Quebec, Canada, 10 years before and 10 years after the introduction of serogroup C conjugate vaccination.

Methodology

IMD cases reported to the provincial notifiable disease registry in 1991–2011 and isolates submitted for laboratory surveillance in 1997–2011 were analysed. Serogrouping, PCR testing and assignment of isolates to sequence types (ST) by using multilocus sequence typing (MLST) were performed.

Results

Yearly overall IMD incidence rates ranged from 2.2–2.3/100,000 in 1991–1992 to 0.49/100,000 in 1999–2000, increasing to 1.04/100,000 in 2011. Among the 945 IMD cases identified by laboratory surveillance in 1997–2011, 68%, 20%, 8%, and 3% were due to serogroups B, C, Y, and W135, respectively. Serogroup C IMD almost disappeared following the implementation of universal childhood immunization with monovalent C conjugate vaccines in 2002. Serogroup B has been responsible for 88% of all IMD cases and 61% of all IMD deaths over the last 3 years. The number and proportion of ST-269 clonal complex has been steadily increasing among the identified clonal complexes of serogroup B IMD since its first identification in 2003, representing 65% of serogroup B IMD in 2011. This clonal complex was first introduced in adolescent and young adults, then spread to other age groups.

Conclusion

Important changes in the epidemiology of IMD have been observed in Quebec during the last two decades. Serogroup C has been virtually eliminated. In recent years, most cases have been caused by the serogroup B ST-269 clonal complex. Although overall burden of IMD is low, the use of a vaccine with potential broad-spectrum coverage could further reduce the burden of disease. Acceptability, feasibility and cost-effectiveness studies coupled with ongoing clinical and molecular surveillance are necessary in guiding public policy decisions.

Clonal analysis of Neisseria meningitidis serogroup B strains in South Africa, 2002 to 2006: emergence of new clone ST-4240/6688

From August 1999 through July 2002, hyperinvasive Neisseria meningitidis serogroup B (MenB) clonal complexes (CCs), namely, ST-32/ET-5 (CC32) and ST-41/44/lineage 3 (CC41/44), were predominant in the Western Cape Province of South Africa. This study analyzed MenB invasive isolates from a national laboratory-based surveillance system that were collected from January 2002 through December 2006. Isolates were characterized by pulsed-field gel electrophoresis (PFGE) (n = 302), and multilocus sequence typing (MLST) and PorA and FetA typing were performed on randomly selected isolates (34/302, 11%). In total, 2,400 cases were reported, with the highest numbers from Gauteng Province (1,307/2,400, 54%) and Western Cape Province (393/2,400, 16%); 67% (1,617/2,400) had viable isolates and 19% (307/1,617) were identified as serogroup B. MenB incidence remained stable over time (P = 0.77) (average incidence, 0.13/100,000 population [range, 0.10 to 0.16/100,000 population]). PFGE (302/307, 98%) divided isolates (206/302, 68%) into 13 clusters and 96 outliers. The largest cluster, B1, accounted for 25% of isolates (76/302) over the study period; its prevalence decreased from 43% (20/47) in 2002 to 13% (8/62) in 2006 (P < 0.001), and it was common in the Western Cape (58/76, 76%). Clusters B2 and B3 accounted for 10% (31/302) and 6% (19/302), respectively, and showed no significant change over time and were predominant in Gauteng. Randomly selected isolates from clusters B1, B2, and B3 belonged to CC32, CC41/44, and the new CC4240/6688, respectively. Overall, 15 PorA and 12 FetA types were identified. MenB isolates were mostly diverse with no single dominant clone; however, CC32 and CC41/44 accounted for 35% and the new CC4240/6688 was the third most prevalent clone.

Characterization of Neisseria meningitidis isolates from Egypt using multilocus sequence typing

To characterize Neisseria meningitidis isolates collected from cerebrospinal fluid of meningitis cases in Egypt (1998-2003) as part of surveillance studies, 67 isolates were serogrouped, tested for antibiotic sensitivity and analyzed using multilocus sequence typing (MLST). Results show that isolates expressing serogroup B (50.7%) and serogroup A (34.3%) antigens were predominant in Egypt during the surveillance period, possibly due to suppression of other serogroups by meningococcal vaccines in current use. Intermediate resistance to penicillin was observed in 71% of the isolates, suggesting a need for physicians to shift to third-generation cephalosporins during the empirical treatment of infection. Recurrent lineages of N. meningitidis in Egypt appear to originate from Europe and other Middle Eastern countries. Of 19 sequence types detected, five were unique to Africa and 10 were not observed previously in the MLST database. The information obtained illustrates the changing dynamics of meningitis after vaccine introduction in Egypt.

Meningococcal conjugate vaccines: optimizing global impact

Meningococcal conjugate vaccines have several advantages over polysaccharide vaccines, including the ability to induce greater antibody persistence, avidity, immunologic memory, and herd immunity. Since 1999, meningococcal conjugate vaccine programs have been established across the globe. Many of these vaccination programs have resulted in significant decline in meningococcal disease in several countries. Recent introduction of serogroup A conjugate vaccine in Africa offers the potential to eliminate meningococcal disease as a public health problem in Africa. However, the duration of immune response and the development of widespread herd immunity in the population remain important questions for meningococcal vaccine programs. Because of the unique epidemiology of meningococcal disease around the world, the optimal vaccination strategy for long-term disease prevention will vary by country.

Potential of recombinant opa proteins as vaccine candidates against hyperinvasive meningococci

Neisseria meningitidis causes half a million cases of septicemia and meningitis globally each year. The opacity (Opa) integral outer membrane proteins from N. meningitidis are polymorphic and highly immunogenic. Particular combinations of Opa proteins are associated with the hyperinvasive meningococcal lineages that have caused the majority of serogroup B and C meningococcal disease in industrialized countries over the last 60 years. For the first time, this genetic structuring of a diverse outer membrane protein family has been used to select a novel combination of representative antigens for immunogenicity testing. Fourteen recombinant Opa variants were produced and used in murine immunizations inducing an increase in specific antimeningococcal total IgG levels. All 14 Opa proteins elicited bactericidal antibodies against at least one hyperinvasive meningococcal isolate, and most isolates from each hyperinvasive lineage were killed by at least one Opa antiserum at a titer of 1:16 or greater. Cross-reactive bactericidal antibody responses were observed among clonal complexes. A theoretical coverage of 90% can be achieved by using a particular combination of 6 Opa proteins against an isolate collection of 227 recent United Kingdom disease cases. This study indicates the potential of Opa proteins to provide broad coverage against multiple meningococcal hyperinvasive lineages.

Detection of a geographical and endemic cluster of hyper-invasive meningococcal strains

From 2006 to December 2009, 45 out of the 513 strains isolated from patients with invasive meningococcal disease in Belgium, were identified as Neisseria meningitidis serogroup B, non-serotypeable, subtype P1.14 (B:NT:P1.14). Most cases were geographically clustered in the northern part of the country. Multilocus Sequence Typing and antigen gene sequencing combined with Pulsed-Field Gel electrophoresis were used to investigate this cluster. Molecular typing showed that 39 out of these 45 N. meningitidis strains belonged to the clonal complex cc-269. The presence of the same PorA Variable Regions (VR1-VR2: 22, 14), the FetA allele (F5-1) and the highly similar Pulsed-Field Gel Electrophoresis profiles, supported genetic relatedness for 38 out of these 39 isolates. Retrospective analysis of B:NT:P1.22,14 isolates from 1999 onwards suggested that these strains belonging to the cc-269 complex, first emerged in the Belgian province of West-Flanders in 2004. This study showed that the combination of molecular tools with classical methods enabled reliable outbreak detection as well as a cluster identification.

Epidemiology of invasive meningococcal disease with decreased susceptibility to penicillin in Ontario, Canada, 2000 to 2006

Neisseria meningitidis has been relatively slow to acquire resistance to penicillin. We previously reported an increase in the incidence of invasive meningococcal disease (IMD) strains with decreased susceptibility to penicillin (DSP) in Ontario. Our objectives were to evaluate trends in IMD with DSP, to identify case-level predictors of IMD with DSP, and to evaluate the relationship among DSP, bacterial phenotype, and the likelihood of a fatal outcome. All IMD isolates received in Ontario between 2000 and 2006 were submitted to the Public Health Laboratories, Toronto, for confirmation of the species, serogroup determination, and susceptibility testing. Isolates were considered to be IMD strains with DSP if the penicillin MIC was > or =0.125 microg/ml. Temporal trends were evaluated using multivariable Poisson regression models. Correlates of diminished susceptibility and fatal outcome were evaluated with multivariable logistic regression models. The overall rate of IMD caused by strains with DSP in Ontario was approximately 1.20 cases per million population annually (95% confidence interval [95% CI], 0.99 to 1.46). Seventy-nine strains (21.7%) were IMD strains with DSP. There was no year-to-year trend in the incidence of IMD with DSP. IMD with DSP was strongly associated with strains of serogroups Y (odds ratio [OR], 6.3; 95% CI, 3.6 to 11.1) and W-135 (OR, 8.2; 95% CI, 4.0 to 16.7). Infection with serogroup B or C strains was associated with a marked increase in the risk of mortality (OR, 3.07; 95% CI, 1.39 to 6.75); however, no association between IMD with DSP and mortality was observed. In contrast to trends of the 1990s, the incidence of IMD with DSP was stable in Ontario between 2000 and 2006. In Ontario, the serogroup rather than the penicillin MIC is the microbiological parameter most predictive of mortality.

The influence of IS1301 in the capsule biosynthesis locus on meningococcal carriage and disease

Previously we have shown that insertion of IS1301 in the sia/ctr intergenic region (IGR) of serogroup C Neisseria meningitidis (MenC) isolates from Spain confers increased resistance against complement-mediated killing. Here we investigate the significance of IS1301 in the same location in N. meningitidis isolates from the UK. PCR and sequencing was used to screen a collection of more than 1500 meningococcal carriage and disease isolates from the UK for the presence of IS1301 in the IGR. IS1301 was not identified in the IGR among vaccine failure strains but was frequently found in serogroup B isolates (MenB) from clonal complex 269 (cc269). Almost all IS1301 insertions in cc269 were associated with novel polymorphisms, and did not change capsule expression or resistance to human complement. After excluding sequence types (STs) distant from the central genotype within cc269, there was no significant difference for the presence of IS1301 in the IGR of carriage isolates compared to disease isolates. Isolates with insertion of IS1301 in the IGR are not responsible for MenC disease in UK vaccine failures. Novel polymorphisms associated with IS1301 in the IGR of UK MenB isolates do not lead to the resistance phenotype seen for IS1301 in the IGR of MenC isolates.

Influence of two vaccination campaigns on genetic diversity of invasive Neisseria meningitidis isolates in northern Spain (1997-2008)

Background

Neisseria meningitidis diversifies rapidly, due to its high recombination rates. The aim of this study was to analyze the possible impact of two vaccination campaigns (a once-off A/C polysaccharide vaccination campaign in people aged 18 months to 20 years old in 1997, and a meningococcal C conjugate vaccination campaign in children aged ≤6 years old from 2000 to 2008) on diversification of the population of invasive isolates obtained between 1997 and 2008. All of the 461 available isolates were included (2, 319, 123, 11 and 6 belonging to serogroups A, B, C, Y and W-135, respectively).

Methodology/Principal Findings

The isolates were analyzed for diversity using multilocus sequence typing, eBURST and the S.T.A.R.T.2 program. One hundred and seven sequence types (ST) and 20 clonal complexes were obtained. Five different STs (ST11, ST8, ST33, ST1163 and ST3496) included 56.4% of the isolates. With the exception of ST11, all other STs were associated with a specific serogroup. Epidemic circulation of serogroup C ST8 isolates was detected in 1997–1998, as well as epidemic circulation of ST11 isolates (serogroups B and C) in 2002–2004. The epidemic behavior of serogroup B ST11 (ST11_B:2a:P1.5) was similar, although with lesser intensity, to that of ST11 of serogroup C. Although clonality increased during epidemic years, the overall diversity of the meningococcal population did not increase throughout the 12 years of the study.

Conclusion

The overall diversity of the meningococcal population, measured by the frequency of STs and clonal complexes, numbers of alleles, polymorphic sites, and index of association, remained relatively constant throughout the study period, contradicting previous findings by other researchers.

Distribution of surface-protein variants of hyperinvasive meningococci in China

OBJECTIVE

Information regarding the different types of FetA and PorB meningococci that circulate in various regions of the world is still scarce. The present study investigated the distribution of FetA and PorB variable region (VR) types among meningococci belonging to hyperinvasive lineages circulating in China.

METHODS

The approach consisted of genotypic analysis of 201 Neisseria meningitidis strains belonging to hyperinvasive lineages isolated in China during the period 1956-2006.

RESULTS

Sixteen different PorB types were found, 8 of which were newly identified. Of the 24 different FetA VR types, 3 were determined to be novel. Particular combinations of FetA and PorB types associated with distinct clonal complexes were also observed. Most cases of invasive disease were caused by five individual clones: A: P1.7-1,10: F5-5: ST-3 (cc1) with P3.6,11,10,7 (class 3 PorB protein; VR1-6, VR2-11, VR3-10, and VR4-7); A: P1.20,9: F3-1: ST-5 (cc5) with P3.4,11,10,7; A: P1.20,9: F3-1: ST-5 (cc5) with P3.9,11,10,7; A: P1.20,9: F3-1: ST-7 (cc5) with P3.4,11,10,7; and C: P1.7-2,14: F3-3: ST-4821 (cc4821) with P3.9,15,6,7.

CONCLUSION

A number of antigen-gene variants and combinations exhibited broad temporal and geographic distributions, although several invasive clones were mainly associated with a specified timeframe. The changes that are increasingly emerging in circulating strains and the prevalent clone replacement describe the molecular epidemiology of meningococcal disease in China. Our findings have implications for both public-health monitoring and further study of this organism.

Target gene sequencing to characterize the penicillin G susceptibility of Neisseria meningitidis

Clinical isolates of Neisseria meningitidis with reduced susceptibility to penicillin G (intermediate isolates, Pen(I)) harbor alterations in the penA gene encoding the penicillin binding protein 2 (PBP2). A 402-bp DNA fragment in the 3' half of penA was sequenced from a collection of 1,670 meningococcal clinical isolates from 22 countries that spanned 60 years. Phenotyping, genotyping, and the determination of MICs of penicillin G were also performed. A total of 139 different penA alleles were detected with 38 alleles that were highly related, clustered together in maximum-likelihood analysis and corresponded to the penicillin G-susceptible isolates. The remaining 101 penA alleles were highly diverse, corresponded to different genotypes or phenotypes, and accounted for 38% of isolates, but no clonal expansion was detected. Analysis of the altered alleles that were represented by at least five isolates showed high correlation with the Pen(I) phenotype. The deduced amino acid sequence of the corresponding PBP2 comprised five amino acid residues that were always altered. This correlation was not complete for rare alleles, suggesting that other mechanisms may also be involved in conferring reduced susceptibility to penicillin. Evidence of mosaic structures through events of interspecies recombination was also detected in altered alleles. A new website was created based on the data from this work (http://neisseria.org/nm/typing/penA). These data argue for the use of penA sequencing to identify isolates with reduced susceptibility to penicillin G and as a tool to improve typing of meningococcal isolates, as well as to analyze DNA exchange among Neisseria species.

Protective meningococcal capsular polysaccharide epitopes and the role of O acetylation

Previous studies with group C meningococcal polysaccharide-tetanus toxoid (GCMP-TT) conjugates had suggested that the GCMP O-acetyl group masked the protective epitope for group C meningococci through steric hindrance or altered conformations. For this report, we confirmed this phenomenon and performed comparative studies with group Y meningococcal polysaccharide (GYMP)-TT to determine whether it might extend to other serogroups. The de-O-acetylated (dOA) polysaccharides (PSs) resulted in higher serum bactericidal activities (SBA) towards the O-acetylated (OA) meningococcal strains from the respective serogroups. High-resolution H-nuclear magnetic resonance spectroscopy at 500 MHz and competitive inhibition serum bactericidal assays were used to characterize the nature of the protective epitope. In head-to-head comparisons with OA PSs as SBA inhibitors, the dOA PSs provided 10 to 1,000 times better inhibition for GCMP in human and mouse antisera and 6 to 13 times better inhibition for GYMP in mouse antisera, using OA strains in all assays. In addition, the SBA for OA strains was highly correlated with dOA PS-specific immunoglobulin G (r=0.72 to 0.98) for both GCMP and GYMP. The results suggest that there may be a generalized role for the O-acetyl group to provide an epitope of misdirected immunogenicity for meningococcal PS capsules, enabling escape from immune surveillance. In addition to greater chemical consistency, the dOA forms of GCMP and GYMP conjugate vaccines endow greater immunologic competence to the PSs, rendering them capable of eliciting higher levels of functional antibodies toward the protective epitopes.

Neisseria meningitidis sequence type and risk for death, Iceland

Invasive meningococcal infections are hyperendemic in Iceland, a relatively isolated country in the mid-Atlantic. We performed a nationwide study on all viable meningococcal strains (N = 362) from 1977 to 2004. We analyzed the association of patient's age and sex, meningococcal serogroups, and sequence types (STs) with outcomes. Overall, 59 different STs were identified, 19 of which were unique to Iceland. The most common STs were 32 (24.6%), 11 (19.9%), and 10 (10.2%). The unique ST-3492 ranked fourth (7.7%). The most common serogroups were B (56.4%), C (39.8%), and A (2.2%). Age (p<0.001) and infection with a unique ST (p = 0.011) were independently associated with increased death rates, whereas isolation of meningococci from cerebrospinal fluid only was associated with lower death rates (p = 0.046). This study shows evolutionary trends of meningococcal isolates in a relatively isolated community and highlights an association between unique STs and poor outcome.

Invasive meningococcal disease in Quebec, Canada, due to an emerging clone of ST-269 serogroup B meningococci with serotype antigen 17 and serosubtype antigen P1.19 (B:17:P1.19)

During periods of endemic meningococcal disease, serogroup B Neisseria meningitidis is responsible for a significant percentage of invasive diseases, and no particular clone or strain predominates (F. E. Ashton and D. A. Caugant, Can. J. Microbiol. 47: 293-289, 2001), However, in the winter of 2004 to 2005, a cluster of serogroup B meningococcal disease occurred in one region in the province of Québec, Canada. The N. meningitidis strain responsible for this cluster of cases was identified as sequence type ST-269 with the antigenic formula B:17:P1.19. Retrospective analysis of isolates from 2000 onwards showed that this clone first emerged in the province of Québec in 2003. The emergence of this clone of serogroup B meningococci occurred after a mass vaccination against serogroup C N. meningitidis, suggesting possible capsule replacement.

Mucosal immunity and optimizing protection with meningococcal serogroup B vaccines

Candidate Neisseria meningitidis serogroup B vaccines that are based on outer-membrane vesicles induce protective immunity in adults but provide neither crossprotection for infants nor long-lasting immunity. We suggest that this lack of vaccine efficacy is not solely because the best antigens are yet to be identified but also results from inappropriate programming of the immune response. Natural carriage of N. meningitidis and related bacteria leads to the development of protective immunity both at the mucosal surface and in the circulation. We propose that vaccine strategies that mimic this natural immunization process would better-optimize vaccine-induced protective immunity. Thus, mucosal immunization before a systemic booster vaccination could provide the solution and reduce the necessity for multiple injections to achieve immunity.