Sequencing of the porB gene: a step toward a true characterization of Neisseria meningitidis

Abstract

Variations in class 2/3 (PorB) proteins form the basis for meningococcal serotyping. Antibodies against these proteins are bactericidal, making serotyping results useful not only for epidemiological surveillance of meningococcal disease but also for identifying potential vaccine components. A total of 20 to 60% of meningococcal B and C isolates from any given population are nontypeable (NT) using a panel of monoclonal antibodies. To analyze the mechanisms responsible for the nonserotypeability characteristic in Neisseria meningitidis, we (i) established the nucleotide sequences of porB gene in 146 meningococcal strains (95 not recognized by the serotyping panel), (ii) identified 18 new allelic variants of the porB gene, (iii) correlated allelic variants with serotypes, (iv) suggest the nontypeability characteristic in those 95 NT strains, and (v) reject the possibility of variation in the levels of PorB expression.

FIG. 1.

Split decomposition analysis of the 146 porB gene sequences obtained from 146 meningococcal strains. Split graphs were drawn from a Hamming (uncorrected) distance matrix of aligned porB gene sequences by using SplitsTree version 3.2 (8). Branch lengths are drawn to scale. To the right, an amplification of the node corresponding to the porB3 sequences is included showing the absence of networks.

FIG. 2.

Western blot of PorB protein from four NT strains (lanes 1, 2, 3, and 5) and one typeable strain (lane 4) revealed with MAb 15. Lanes 1 to 4, strains with the allelic variant porB3-84; lane 5, strain with the allelic variant porB3-87.