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Antigenic diversity of meningococcal outer membrane protein PorA has implications for epidemiological analysis and
1Division of Bacteriology, National Institute for Biological Standards and Control, Potters Bar, Hertfordshire, United Kingdom.
Abstract:
The currently used serological subtyping scheme for the pathogen Neisseria meningitidis is not comprehensive, a proportion of isolates are reported as not subtypeable (NST), and few isolates are fully characterized with two subtypes for each strain. To establish the reasons for this and to assess the effectiveness of DNA-based subtyping schemes, dot blot hybridization and nucleotide sequence analyses were used to characterize the genes encoding antigenic variants of the meningococcal subtyping antigen, the PorA protein. A total of 233 strains, including 174 serologically NST and 59 partially or completely subtyped meningococcal strains, were surveyed. The NST isolates were chosen to be temporally and geographically representative of NST strains, isolated in England and Wales, and submitted to the Meningococcal Reference Unit in the period 1989 to 1991. The DNA-based analyses demonstrated that all of the strains examined possessed a porA gene. Some of these strains were serologically NST because of a lack of monoclonal antibodies against certain PorA epitopes; in other cases, strains expressed minor variants of known PorA epitopes that did not react with monoclonal antibodies in serological assays. Lack of expression remained a possible explanation for serological typing failure in some cases. These findings have important implications for epidemiological analysis and vaccine design and demonstrate the need for genetic characterization, rather than phenotypic characterization using monoclonal antibodies, for the identification of meningococcal strains.
Insights
Serological subtyping of Neisseria meningitidis is limited. DNA-based methods reveal genetic variations in the PorA protein, explaining why some strains are not subtypeable and highlighting the need for genetic characterization in meningococcal epidemiology and vaccine development.
Area of Science:
- Microbiology
- Genetics
- Immunology
Background:
- The current serological subtyping of Neisseria meningitidis is insufficient, leading to many "not subtypeable" (NST) isolates.
- Limited characterization hinders epidemiological tracking and vaccine development for meningococcal disease.
Purpose of the Study:
- To investigate the reasons behind the limitations of serological subtyping for Neisseria meningitidis.
- To evaluate the efficacy of DNA-based subtyping schemes for meningococcal strain characterization.
Main Methods:
- Utilized dot blot hybridization and nucleotide sequence analysis to characterize the genes encoding the PorA protein in 233 Neisseria meningitidis strains.
- Included 174 serologically NST strains and 59 partially or fully subtyped strains, representative of isolates from England and Wales (1989-1991).
Main Results:
- All examined Neisseria meningitidis strains possessed the porA gene.
- Serological non-subtypeability was often due to a lack of specific monoclonal antibodies or minor PorA epitope variants.
- In some instances, failure of serological typing could be attributed to a lack of PorA expression.
Conclusions:
- DNA-based characterization of the porA gene is crucial for accurate Neisseria meningitidis identification.
- Genetic analysis provides a more comprehensive understanding of meningococcal strains than serological methods alone.
- Findings impact meningococcal epidemiological surveillance and inform the design of effective vaccines.