Antigenic-variation of the class I outer membrane protein in hyperendemic Neisseria meningitidis strains in the Netherlands

Since 1980, the number of cases of meningococcal disease caused by serogrou p B isolates with the P1.4 serosubtype has greatly increased in The Netherl ands. Screening for this serosubtype in the strain collection of The Nether lands Reference Laboratory for Bacterial Meningitis revealed that a low num ber of P1.4 strains had been present in the Dutch meningococcal population since 1965. Genotyping of P1.4 strains showed that one cluster of strains, the hyperendemic lineage III (D. A. Caugant et al., J. Infect. Dis. 162:867 -874, 1990), is responsible for the increase since 1980. The diversity of t he porA genes, which encode the P1 protein on which serosubtyping is based, was studied for genotypically different P1.4 strains and for lineage III s trains expressing antigenically different P1 proteins. Sequence analysis sh owed that porA genes of genotypically distinct strains that express antigen ically indistinguishable P1 proteins are identical only in the epitope-enco ding region, suggesting that this region has spread through the meningococc al population via horizontal gene transfer. Analysis of porA genes of linea ge III strains showed that both horizontal gene transfer and partial deleti on of the epitope-encoding region may contribute to the different antigenic properties for P1 of these strains, Phase variation of expression of the p orA gene seems to account for most nonreacting strains. These results show that serosubtyping may underestimate the rise of a hyperendemic clone.