Description and nomenclature of Neisseria meningitidis capsule locus.
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ABSTRACT:
SUBMITTER: Harrison OB
PROVIDER: S-EPMC3647402 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The different sialic acid (serogroups B, C, Y, and W-135) and nonsialic acid (serogroup A) capsular polysaccharides expressed by Neisseria meningitidis are major virulence factors and are used as epidemiologic markers and vaccine targets. However, the identification of meningococcal isolates with similar genetic markers but expressing different capsular polysaccharides suggests that meningococcal clones can switch the type of capsule they express. We identified, except for capsule, isogenic serogroups B [(alpha2-->8)-linked polysialic acid] and C [(alpha2-->9)-linked polysialic acid] meningococcal isolates from an outbreak of meningococcal disease in the U. S. Pacific Northwest. We used these isolates and prototype serogroup A, B, C, Y, and W-135 strains to define the capsular biosynthetic and transport operons of the major meningococcal serogroups and to show that switching from the B to C capsule in the outbreak strain was the result of allelic exchange of the polysialyltransferase. Capsule switching was probably the result of transformation and horizontal DNA exchange in vivo of a serogroup C capsule biosynthetic operon. These findings indicate that closely related virulent meningococcal clones may not be recognized by traditional serogroup-based surveillance and can escape vaccine-induced or natural protective immunity by capsule switching. Capsule switching may be an important virulence mechanism of meningococci and other encapsulated bacterial pathogens. As vaccine development progresses and broader immunization with capsular polysaccharide conjugate vaccines becomes a reality, the ability to switch capsular types may have important implications for the impact of these vaccines.
| S-EPMC19312 | biostudies-literature
Project description:Background: Expression of a capsule from one of serogroups A, B, C, W, X or Y is usually required for Neisseria meningitidis ( Nme) to cause invasive meningococcal disease. The capsule is encoded by the capsule locus, cps, which is proposed to have been acquired by a formerly capsule null organism by horizontal genetic transfer (HGT) from another species. Following identification of putative capsule genes in non-pathogenic Neisseria species, this hypothesis is re-examined. Methods: Whole genome sequence data from Neisseria species, including Nme genomes from a diverse range of clonal complexes and capsule genogroups, and non- Neisseria species, were obtained from PubMLST and GenBank. Sequence alignments of genes from the meningococcal cps, and predicted orthologues in other species, were analysed using Neighbor-nets, BOOTSCANing and maximum likelihood phylogenies. Results: The meningococcal cps was highly mosaic within regions B, C and D. A subset of sequences within regions B and C were phylogenetically nested within homologous sequences belonging to N. subflava, consistent with HGT event in which N. subflava was the donor. In the cps of 23/39 isolates, the two copies of region D were highly divergent, with rfbABC' sequences being more closely related to predicted orthologues in the proposed species N. weixii (GenBank accession number CP023429.1) than the same genes in Nme isolates lacking a capsule. There was also evidence of mosaicism in the rfbABC' sequences of the remaining 16 isolates, as well as rfbABC from many isolates. Conclusions: Data are consistent with the en bloc acquisition of cps in meningococci from N. subflava, followed by further recombination events with other Neisseria species. Nevertheless, the data cannot refute an alternative model, in which native meningococcal capsule existed prior to undergoing HGT with N. subflava and other species. Within-genus recombination events may have given rise to the diversity of meningococcal capsule serogroups.
| S-EPMC6619384 | biostudies-literature
Project description:Neisseria meningitidis isolates are conventionally classified by serosubtyping, which characterizes the reactivities of the PorA outer membrane protein variable-region (VR) epitopes with monoclonal antibodies (MAbs). A newer method (PorA VR typing) uses predicted amino acid sequences derived from DNA sequence analysis. The resulting classification schemes are not standardized, offering conflicting and sometimes irreconcilable data from the two methods. In this paper, we propose a standardization of the PorA VR typing nomenclature that incorporates serologic information from traditional PorA serosubtyping with molecular data from predicted VR sequences. We performed a comprehensive literature and database search, generating a collection of strains and DNA sequences that reflects the diversity within PorA that exists to date. We have arranged this information in a comprehensive logical model that includes both serosubtype and PorA VR type assignments. Our data demonstrate that the current panel of serosubtype-defining MAbs underestimates PorA VR variability by at least 50%. Our proposal for VR typing is informative because amino acid sequence and serologic information, when serosubtype-defining MAbs are available, can be deduced simultaneously from the PorA VR designation. This scheme will be useful in future classification and applied epidemiologic studies of N. meningitidis, being a systematic way of selecting PorA vaccine candidates and analyzing vaccine coverage and failure.
| S-EPMC96214 | biostudies-literature
Project description:Neisseria meningitidis is a commensal and accidental pathogen exclusively of humans. Although the production of polysaccharide capsules is considered to be essential for meningococcal virulence, there have been reports of constitutively unencapsulated strains causing invasive meningococcal disease (IMD). Here we report the genome sequence of a capsule null locus (cnl) strain of sequence type 198 (ST-198), which is found in half of the reported cases of IMD caused by cnl meningococcal strains.
| S-EPMC3430344 | biostudies-other
Project description:Neisseria meningitidis is the only lipopolysaccharide (LPS)-producing gram-negative bacterial species shown to be viable also without LPS. It was thought that the presence of capsular polysaccharide is necessary for this unusual feature. However, we show now that no part of the capsule gene cluster is required for maintaining LPS deficiency in N. meningitidis.
| S-EPMC1231088 | biostudies-literature
Project description:The meningococcal capsule is an important virulence determinant. Unencapsulated meningococci lacking capsule biosynthesis genes and containing the capsule null locus (cnl) are predominantly non-pathogenic. Rare cases of invasive meningococcal disease caused by cnl isolates belonging to sequence types (ST) and clonal complexes (cc) ST-845 (cc845), ST-198 (cc198), ST-192 (cc192) and ST-53 (cc53) have been documented. The clinical significance of these isolates however remains unclear. We identified four invasive cnl meningococci through laboratory-based surveillance in South Africa from 2003 through 2013, which we aimed to characterize using whole genome data.One isolate [NG: P1.7-2,30: F1-2: ST-53 (cc53)] contained cnl allele 12, and caused empyema in an adult male with bronchiectasis from tuberculosis, diabetes mellitus and a smoking history. Three isolates were NG: P1.18-11,42-2: F?: ST-192 (cc192) and contained cnl allele 2. One patient was an adolescent male with meningitis. The remaining two isolates were from recurrent disease episodes (8 months apart) in a male child with deficiency of the sixth complement component, and with the exception of two single nucleotide polymorphisms, contained identical core genomes. The ST-53 (cc53) isolate possessed alleles for NHBA peptide 191 and fHbp variant 2; whilst the ST-192 (cc192) isolates contained NHBA peptide 704 and fHbp variant 3. All four isolates lacked nadA. Comparison of the South African genomes to 61 additional cnl genomes on the PubMLST Neisseria database ( http://pubmlst.org/neisseria/ ), determined that most putative virulence genes could be found in both invasive and carriage phenotypes.Although rare, invasive disease by cnl meningococci may be associated with host immunodeficiency and such patients may benefit from protein-based meningococcal vaccines.
| S-EPMC5320719 | biostudies-literature
Project description:In Neisseria meningitidis, translocation of capsular polysaccharides to the cell surface is mediated by a transport system that fits the characteristics of ABC (ATP-binding cassette) transporters. One protein of this transport system, termed CtrA, is located in the outer membrane. By use of a CtrA-specific monoclonal antibody, we could demonstrate that CtrA occurs exclusively in N. meningitidis and not in other pathogenic or nonpathogenic Neisseria species. Nucleotide sequence comparison of the ctrA gene from different meningococcal serogroups indicated that CtrA is strongly conserved in all meningococcal serogroups, independent of the chemical composition of the capsular polysaccharide. Secondary structure analysis revealed that CtrA is anchored in the outer membrane by eight membrane-spanning amphipathic beta strands, a structure of proteins that function as porins.
| S-EPMC257557 | biostudies-other
Project description:While much data exist in the literature about how Neisseria meningitidis adheres to and invades human cells, its behavior inside the host cell is largely unknown. One of the essential meningococcal attributes for pathogenesis is the polysaccharide capsule, which has been shown to be important for bacterial survival in extracellular fluids. To investigate the role of the meningococcal capsule in intracellular survival, we used B1940, a serogroup B strain, and its isogenic derivatives, which lack either the capsule or both the capsule and the lipooligosaccharide outer core, to infect human phagocytic and nonphagocytic cells and monitor invasion and intracellular growth. Our data indicate that the capsule, which negatively affects bacterial adhesion and, consequently, entry, is, in contrast, fundamental for the intracellular survival of this microorganism. The results of in vitro assays suggest that an increased resistance to cationic antimicrobial peptides (CAMPs), important components of the host innate defense system against microbial infections, is a possible mechanism by which the capsule protects the meningococci in the intracellular environment. Indeed, unencapsulated bacteria were more susceptible than encapsulated bacteria to defensins, cathelicidins, protegrins, and polymyxin B, which has long been used as a model compound to define the mechanism of action of CAMPs. We also demonstrate that both the capsular genes (siaD and lipA) and those encoding an efflux pump involved in resistance to CAMPs (mtrCDE) were up-regulated during the intracellular phase of the infectious cycle.
| S-EPMC1932921 | biostudies-literature
Project description:Changing antigenic structure such as with capsule polysaccharide is a common strategy for bacterial pathogens to evade a host immune system. The recent emergence of an invasive W:2a:P1.7-2,4 sequence type 11 (ST-11) strain of Neisseria meningitidis in New Zealand, an uncommon serogroup/serotype in New Zealand disease cases, was investigated for its genetic origins. Molecular typing of 107 meningococcal isolates with similar serotyping characteristics was undertaken to determine genetic relationships. Results indicated that the W:2a:P1.7-2,4 strain had emerged via capsule switching from a group C strain (C:2a:P1.7-2,4). Neither the upstream nor downstream sites of recombination could be elucidated, but sequence analysis demonstrated that at least 45 kb of DNA was involved in the recombination, including the entire capsule gene cluster. The oatWY gene carried by the W:2a:P1.7-2,4 strain contained the insertion sequence element IS1301, one of five variants of oatWY found in group W135 strains belonging to the carriage-associated ST-22 clonal complex. This suggested that the origin of the capsule genes carried by the invasive W:2a:P1.7-2,4 strain is carriage associated. These results provide novel evidence for the long-standing dogma that disease-associated strains acquire antigenic structure from carriage-associated strains. Moreover, the capsule switch described here has arisen from the exchange of the entire capsule locus.
| S-EPMC2708544 | biostudies-literature
Project description:Pathogenic meningococci have acquired a 24 kb capsule synthesis island (cps) by horizontal gene transfer which consists of a synthetic locus and associated capsule transport genes flanked by repetitive Regions D and D'. Regions D and D' contain an intact gene encoding a UDP-galactose epimerase (galE1) and a truncated remnant (galE2), respectively. In this study, GalE protein alleles were shown to be either mono-functional, synthesising UDP-galactose (UDP-Gal), or bi-functional, synthesising UDP-Gal and UDP-galactosamine (UDP-GalNAc). Meningococci possessing a capsule null locus (cnl) typically possessed a single bi-functional galE. Separation of functionality between galE1 and galE2 alleles in meningococcal isolates was retained for all serogroups except serogroup E which has a synthetic requirement for UDP-GalNAc. The truncated galE2 remnant in Region D' was also phylogenetically related to the bi-functional galE of the cnl locus suggesting common ancestry. A model is proposed in which the illegitimate recombination of the cps island into the galE allele of the cnl locus results in the formation of Region D' containing the truncated galE2 locus and the capture of the cps island en bloc. The retention of the duplicated Regions D and D' enables inversion of the synthetic locus within the cps island during bacterial growth.
| S-EPMC5349592 | biostudies-literature