Survival of Neisseria meningitidis outside of the host: environmental effects and differences among strains

Distributed genotyping and clustering of Neisseria strains reveal continual emergence of epidemic meningococcus over a century

Core genome multilocus sequence typing (cgMLST) is commonly used to classify bacterial strains into different types, for taxonomical and epidemiological applications. However, cgMLST schemes require central databases for the nomenclature of new alleles and sequence types, which must be synchronized worldwide and involve increasingly intensive calculation and storage demands. Here, we describe a distributed cgMLST (dcgMLST) scheme that does not require a central database of allelic sequences and apply it to study evolutionary patterns of epidemic and endemic strains of the genus Neisseria. We classify 69,994 worldwide Neisseria strains into multi-level clusters that assign species, lineages, and local disease outbreaks. We divide Neisseria meningitidis into 168 endemic lineages and three epidemic lineages responsible for at least 9 epidemics in the past century. According to our analyses, the epidemic and endemic lineages experienced very different population dynamics in the past 100 years. Epidemic lineages repetitively emerged from endemic lineages, disseminated worldwide, and apparently disappeared rapidly afterward. We propose a stepwise model for the evolutionary trajectory of epidemic lineages in Neisseria, and expect that the development of similar dcgMLST schemes will facilitate epidemiological studies of other bacterial pathogens.

Effect of respiratory tract co-colonizers on initial attachment of Neisseria meningitidis

Respiratory tract is a complex system comprising of unique microbiota inhabitants. Neisseria meningitidis, Staphylococcus aureus, Streptococcus pyogenes, Pseudomonas aeruginosa and Klebsiella pneumoniae are few prevalent bacteria in the community composition during lung infections. Although, N. meningitidis resides asymptomatically in nasopharynx of the human host, it can cause fatal infections like meningitis. However, factors affecting transit from carriage to symptomatic infection are not well understood. Various host metabolites and environmental conditions affect the virulence of bacteria. Here, we report that presence of co-colonizers significantly reduces the initial attachment of N. meningitidis to A549 nasopharyngeal epithelial cells. Further, significant decrease in invasion to A549 nasopharyngeal epithelial cells was observed. Moreover, survival in J774A.1 murine macrophage also increases significantly when conditioned media (CM) from S. pyogenes and L. rhamnosus is used for culturing N. meningitidis. The increase in survival could be attributed to increased capsule synthesis. The gene expression studies revealed increased expression of siaC and ctrB in CM prepared from the growth S. pyogenes and L. rhamnosus. Overall, the results suggest change in the virulence of N. meningitidis is assisted by lung microbiota.

Socioepidemiological macro-determinants associated with the cumulative incidence of bacterial meningitis: A focus on the African Meningitis Belt

Background

Bacterial meningitis (BM) is a public health challenge as it is associated with high lethality and neurological sequelae. Worldwide, most cases are registered in the African Meningitis Belt (AMB). The role of particular socioepidemiological features is essential for understanding disease dynamics and optimizing policy-making.

Objective

To identify socioepidemiological macro-determinants that contribute to explaining the differences in BM incidence between AMB and the rest of Africa.

Methods

Country-level ecologic study based on the cumulative incidence estimates of the Global Burden of Disease study and reports of the MenAfriNet Consortium. Data about relevant socioepidemiological features were extracted from international sources. Multivariate regression models were implemented to define variables associated with the classification of African countries within the AMB and the incidence of BM worldwide.

Results

Cumulative incidences at the AMB sub-regions were 111.93 (west), 87.23 (central), 65.10 (east), and 42.47 (north) per 100,000 population. A pattern of common origin with continuous exposition and seasonality of cases was observed. Socio-epidemiological determinants contributing to differentiating the AMB from the rest of Africa were household occupancy (OR 3.17 CI 95% 1.09-9.22, p = 0.034) and malaria incidence (OR 1.01 CI 95% 1.00-1.02, p = 0.016). BM cumulative incidence worldwide was additionally associated with temperature and gross national income per capita.

Conclusion

Socioeconomic and climate conditions are macro-determinants associated with BM cumulative incidence. Multilevel designs are required to confirm these findings.

Elucidating the Structural and Minimal Protective Epitope of the Serogroup X Meningococcal Capsular Polysaccharide

Despite the considerable progress toward the eradication of meningococcal disease with the introduction of glycoconjugate vaccines, previously unremarkable serogroup X has emerged in recent years, recording several outbreaks throughout the African continent. Different serogroup X polysaccharide-based vaccines have been tested in preclinical trials, establishing the principles for further improvement. To elucidate the antigenic determinants of the MenX capsular polysaccharide, we generated a monoclonal antibody, and its bactericidal nature was confirmed using the rabbit serum bactericidal assay. The antibody was tested by the inhibition enzyme-linked immunosorbent assay and surface plasmon resonance against a set of oligosaccharide fragments of different lengths. The epitope was shown to be contained within five to six α-(1–4) phosphodiester mannosamine repeating units. The molecular interactions between the protective monoclonal antibody and the MenX capsular polysaccharide fragment were further detailed at the atomic level by saturation transfer difference nuclear magnetic resonance (NMR) spectroscopy. The NMR results were used for validation of the in silico docking analysis between the X-ray crystal structure of the antibody (Fab fragment) and the modeled hexamer oligosaccharide. The antibody recognizes the MenX fragment by binding all six repeating units of the oligosaccharide via hydrogen bonding, salt bridges, and hydrophobic interactions. In vivo studies demonstrated that conjugates containing five to six repeating units can produce high functional antibody levels. These results provide an insight into the molecular basis of MenX vaccine-induced protection and highlight the requirements for the epitope-based vaccine design.

Two Cases of Meningococcal Disease in One Family Separated by an Extended Period - Colorado, 2015-2016

On April 26, 2015, a case of meningococcal disease in a woman aged 75 years was reported to the Colorado Department of Public Health and Environment (CDPHE). As part of routine public health investigation and control activities, all seven family contacts of the patient were advised to receive appropriate postexposure prophylaxis (PEP) to eradicate nasopharyngeal carriage of meningococci and prevent secondary disease (1), although it is not known whether the family contacts complied with PEP recommendations. Fifteen months later, on June 6, 2016, CDPHE was notified that the grandchild of the first patient, a male infant aged 3 months who lived with the first patient, also had meningococcal disease. The infant's immediate family members (parents and one sibling) were among family contacts for whom PEP was recommended in 2015. Neisseria meningitidis isolates from both patients were found to be serogroup C at the CDPHE laboratory. Whole genome sequence (WGS) analysis at CDC found that both isolates had the same sequence type, indicating close genetic relatedness. These cases represent a possible instance of meningococcal disease transmission within a family, despite appropriate PEP recommendations and with a long interval between cases.

Increase of Neisseria meningitidis W:cc11 invasive disease in Chile has no correlation with carriage in adolescents

Neisseria meningitidis is a human exclusive pathogen that can lead to invasive meningococcal disease or may be carried in the upper respiratory tract without symptoms. The relationship between carriage and disease remains poorly understood but it is widely accepted that decreasing carriage by immunization should lead to a reduction of invasive cases. Latin America has experienced an increased incidence of serogroup W invasive cases of Neisseria meningitidis in the last decade. Specifically in Chile, despite low total incidence of invasive cases, serogroup W has become predominant since 2011 and has been associated with elevated mortality. Expecting to gain insight into the epidemiology of this disease, this study has used molecular typing schemes to compare Neisseria meningitidis isolates causing invasive disease with those isolates collected from adolescent carriers during the same period in Chile. A lower carriage of the serogroup W clonal complex ST-11/ET37 than expected was found; whereas, the same clonal complex accounted for 66% of total invasive meningococcal disease cases in the country that year. A high diversity of PorA variable regions and fHbp peptides was also ascertained in the carrier isolates compared to the invasive ones. According to the results shown here, the elevated number of serogroup W invasive cases in our country cannot be explained by a rise of carriage of pathogenic isolates. Overall, this study supports the idea that some strains, as W:cc11 found in Chile, possess an enhanced virulence to invade the host. Notwithstanding hypervirulence, this strain has not caused an epidemic in Chile. Finally, as genetic transfer occurs often, close surveillance of Neisseria meningitidis strains causing disease, and particularly hypervirulent W:cc11, should be kept as a priority in our country, in order to prepare the best response to face genetic changes that could lead to enhanced fitness of this pathogen.